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L_0712 | what is science | T_3501 | People have wondered about the natural world for as long as there have been people. So its no surprise that modern science has roots that go back thousands of years. The Table 1.1 describes just a few milestones in the history of science. A much more detailed timeline is available at the link below. Often, new ideas were not accepted at first because they conflicted with accepted views of the world. A good example is Copernicus idea that the sun is the center of the solar system. This idea was rejected at first because people firmly believed that Earth was the center of the solar system and the sun moved around it. Date Scientific Discovery Date 3500 BC Mesopotamian calendar 600 BC Thales 350 BC Aristotle 400 AD to 1000 AD Early Chinese Seismograph Scientific Discovery Several ancient civilizations studied astronomy. They recorded their observations of the movements of stars, the sun, and the moon. We still use the calendar developed by the Mesopotamians about 5500 years ago. It is based on cycles of the moon. The ancient Greek philosopher Thales proposed that natural events, such as lightning and earthquakes, have natural causes. Up until then, people blamed such events on gods or other supernatural causes. Thales has been called the "father of science" for his ideas about the natural world. The Greek philosopher Aristotle argued that truth about the natural world can be discovered through observa- tion and induction. This idea is called empiricism. Aristotles empiricism laid the foundation for the meth- ods of modern science. When Europe went through the Dark Ages, European science withered. However, in other places, science still flourished. For example: In North Africa, the scientist Alhazen studied light. He used experiments to test competing theories about light. In China, scientists invented compasses. They also invented seismographs to measure earth- quakes. They studied astronomy as well. Date Mid-1500s to late 1600s Scientific Discovery The Scientific Revolution occurred in Europe. This was the beginning of modern Western science. Many scientific advances were made during this time. Copernicus proposed that the sun, not Earth, is the center of the solar system. Galileo improved the telescope and made im- portant discoveries in astronomy. He discovered evidence that supported Copernicus theory. Newton proposed the law of gravity. Galileo 2001 Many scientists around the world worked together to complete the genetic sequence of human chromosomes. This amazing feat will help scientists understand, and perhaps someday cure, genetic diseases. Human Chromosomes | text | null |
L_0712 | what is science | T_3502 | Throughout history, women and people of color have rarely had the same chances as white males for education and careers in science. But they have still made important contributions to science. The Table 1.2 gives just a few examples of their contributions to physical science. More contributions are described at these links: Contributor Marie Curie (1867-1934) Description Marie Curie was the first woman to win a Nobel Prize. She won the 1903 Nobel Prize in physics for the discovery of radiation. She won the 1911 Nobel Prize in chemistry for discovering the elements radium and polonium. Contributor Lise Meitner (1878-1968) Description Lise Meitner was one of the scientists who discovered nuclear fission. This is the process that creates enor- mous amounts of energy in nuclear power plants. Irene Joliot-Curie (18971956) Irene Joliot-Curie, daughter of Marie Curie, won the 1935 Nobel prize in chemistry, along with her husband, for the synthesis of new radioactive elements. Maria Goeppert-Mayer (19061972) Maria Goeppert-Mayer was a co-winner of the 1963 Nobel prize in physics for discoveries about the struc- ture of the nucleus of the atom. Ada E. Yonath (1939present) Ada E. Yonath was a co-winner of the 2009 Nobel prize in chemistry. She made important discoveries about ribosomes, the structures in living cells where proteins are made. Contributor Shirley Ann Jackson (1946-present) Description Shirley Ann Jackson earned a doctoral degree in physics. She became the chair of the US Nuclear Regulatory Commission. Ellen Ochoa (1958-present) Ellen Ochoa is an inventor, research scientist, and NASA astronaut. She has flown several space missions. | text | null |
L_0713 | the scope of physical science | T_3503 | Physical science can be defined as the study of matter and energy. Matter refers to all the "stuff" that exists in the universe. It includes everything you can see and many things that you cannot see, including the air around you. Energy is what gives matter the ability to move and change. Energy can take many forms, such as electricity, heat, and light. Physical science can be divided into chemistry and physics. Chemistry focuses on matter and energy at the scale of atoms and molecules. Physics focuses on matter and energy at all scales, from atoms to outer space. | text | null |
L_0713 | the scope of physical science | T_3504 | Chemistry is the study of the structure, properties, and interactions of matter. Important concepts in chemistry include physical changes, such as water freezing, and chemical reactions, such as fireworks exploding. Chemistry concepts can answer all the questions on the left page of the notebook in Figure 1.5. Do you know the answers? | text | null |
L_0713 | the scope of physical science | T_3505 | Physics is the study of energy and how it interacts with matter. Important concepts in physics include motion, forces such as magnetism and gravity, and different forms of energy. Physics concepts can answer all the questions on the right page of the notebook in Figure 1.5. | text | null |
L_0713 | the scope of physical science | T_3506 | Physical science explains much of what you observe and do in your daily life. In fact, you depend on physical science for almost everything that makes modern life possible. You couldnt drive a car, text message, or send a tweet without decades of advances in chemistry and physics. You wouldnt even be able to turn on a light. Figure "hows" and "whys" about them as you read the rest of this book. | text | null |
L_0713 | the scope of physical science | T_3507 | People with training in physical science are employed in a variety of places. There are many career options. Just four are described in Figure 1.7. Many more are described at the URL below. Do any of these careers interest you? http://diplomaguide.com/article_directory/sh/page/Physical%20Science/sh/Job_Titles_and_Careers_List.html . | text | null |
L_0730 | pressure of fluids | T_3612 | All fluids exert pressure like the air inside a tire. The particles of fluids are constantly moving in all directions at random. As the particles move, they keep bumping into each other and into anything else in their path. These collisions cause pressure, and the pressure is exerted equally in all directions. When particles are crowded together in one part of their container, they quickly spread out to fill their container. They always move from an area of higher pressure to an area of lower pressure. Thats why air entering a tire quickly spreads throughout the tire. | text | null |
L_0730 | pressure of fluids | T_3613 | Pressure is the result of force acting on a given area. It can be represented by the equation: Pressure = Force Area Pressure shows how concentrated the force is on a given area. The smaller the area to which force is applied, the greater the pressure is. Think about pressing a pushpin, like the one in Figure 15.2, into a bulletin board. You apply force with your thumb to the broad head of the pushpin. However, the force that the pushpin applies to the bulletin board acts only over the tiny point of the pin. This is a much smaller area, so the pressure the point applies to the bulletin board is much greater than the pressure you apply with you thumb. As a result, the pin penetrates the bulletin board with ease. | text | null |
L_0730 | pressure of fluids | T_3614 | In the equation for pressure, force is expressed in newtons (N) and area is expressed in square meters (m2 ). Therefore, pressure is expressed in N/m2 , which is the SI unit for pressure. This unit is also called the pascal (Pa). It is named for the scientist Blaise Pascal, whose discovery about pressure in fluids is described later in this lesson. Pressure may also be expressed in the kilopascal (kPa), which equals 1000 pascals. For example, the correct air pressure inside a mountain bike tire is usually about 200 kPa. | text | null |
L_0730 | pressure of fluids | T_3615 | When you know how much force is acting on a given area, you can calculate the pressure that is being applied to the area using the equation for pressure given above. For example, assume that a big rock weighs 500 newtons and is resting on the ground on an area of 0.5 m2 . The pressure exerted on the ground by the rock is: Pressure = 500 N = 1000 N/m2 = 1000 Pa, or 1 kPa 0.5 m2 Sometimes pressure but not force is known. To calculate force, the equation for pressure can be rewritten as: Force = Pressure Area For example, suppose another rock exerts 2 kPa of pressure over an area of 0.3 m2 . How much does the rock weigh? Change 2 kPa to 2000 N/m2 and substitute it for pressure in the force equation: Force (Weight) = 2000 N/m2 0.3 m2 = 600 N Problem Solving Problem: A break dancer has a weight of 450 N. She is balancing on the ground on one hand. The palm of her hand has an area of 0.02 m2 . How much pressure does her hand exert on the ground? Solution: Use the equation Pressure = Force Area . Pressure = 450 N = 22500 Pa, or 22.5 kPa 0.02 m2 You Try It! Problem: If the break dancer lies down on the ground on her back, her weight is spread over an area of 0.75 m2 . How much pressure does she exert on the ground in this position? | text | null |
L_0730 | pressure of fluids | T_3616 | Both the water in the ocean and the air in the atmosphere exert pressure because of their moving particles. The ocean and atmosphere also illustrate two factors that affect pressure in fluids: depth and density. A fluid exerts more pressure at greater depths. Deeper in a fluid, all of the fluid above results in more weight pressing down. This causes greater pressure. Denser fluids such as water exert more pressure than less dense fluids such as air. The particles of denser fluids are closer together, so there are more collisions in a given area. This is illustrated in Figure 15.3 for water and air. | text | null |
L_0730 | pressure of fluids | T_3617 | As you go deeper in the ocean, the pressure exerted by the water increases steadily. The diagram in Figure 15.4 shows how pressure changes with depth. For every additional meter below the surface, pressure increases by 10 kPa. At 30 meters below the surface, the pressure is double the pressure at the surface. At a depth greater than 500 meters, the pressure is too great for humans to withstand without special equipment to protect them. Around 9000 meters below the surface, in the deepest part of the ocean, the pressure is tremendous. You can see a video demonstration of changes in water pressure with depth at this URL: (0:42). MEDIA Click image to the left or use the URL below. URL: Because of the pressure of the water, divers who go deeper than about 40 meters below the surface must return to the surface slowly and stop for several minutes at one or more points in their ascent. Thats what the divers in Figure water as they swim closer to the surface. If they were to rise to the surface too quickly, the gases dissolved in their blood would form bubbles and cause serious health problems. | text | null |
L_0730 | pressure of fluids | T_3618 | Like water in the ocean, air in the atmosphere exerts pressure that increases with depth. Most gas molecules in the atmosphere are pulled close to Earths surface by gravity. As a result, air pressure decreases quickly at lower altitudes and then more slowly at higher altitudes. This is illustrated in Figure 15.6. Air pressure is greatest at sea level, where the depth of the atmosphere is greatest. At higher altitudes, the pressure is less because the depth of the atmosphere is less. For example, on top of Mount Everest, the tallest mountain on Earth, air pressure is only about one-third of the pressure at sea level. At such high altitudes, low air pressure makes it hard to breathe and is dangerous to human health. The pressure of air in the atmosphere allows you to do many things, from sipping through a straw to simply breathing (see Figure 15.7). When you first suck on a straw, you remove air from the straw, so the air pressure in the straw is lower than For more examples of how we use air pressure, watch the video at this URL: MEDIA Click image to the left or use the URL below. URL: | text | null |
L_0730 | pressure of fluids | T_3618 | Like water in the ocean, air in the atmosphere exerts pressure that increases with depth. Most gas molecules in the atmosphere are pulled close to Earths surface by gravity. As a result, air pressure decreases quickly at lower altitudes and then more slowly at higher altitudes. This is illustrated in Figure 15.6. Air pressure is greatest at sea level, where the depth of the atmosphere is greatest. At higher altitudes, the pressure is less because the depth of the atmosphere is less. For example, on top of Mount Everest, the tallest mountain on Earth, air pressure is only about one-third of the pressure at sea level. At such high altitudes, low air pressure makes it hard to breathe and is dangerous to human health. The pressure of air in the atmosphere allows you to do many things, from sipping through a straw to simply breathing (see Figure 15.7). When you first suck on a straw, you remove air from the straw, so the air pressure in the straw is lower than For more examples of how we use air pressure, watch the video at this URL: MEDIA Click image to the left or use the URL below. URL: | text | null |
L_0730 | pressure of fluids | T_3618 | Like water in the ocean, air in the atmosphere exerts pressure that increases with depth. Most gas molecules in the atmosphere are pulled close to Earths surface by gravity. As a result, air pressure decreases quickly at lower altitudes and then more slowly at higher altitudes. This is illustrated in Figure 15.6. Air pressure is greatest at sea level, where the depth of the atmosphere is greatest. At higher altitudes, the pressure is less because the depth of the atmosphere is less. For example, on top of Mount Everest, the tallest mountain on Earth, air pressure is only about one-third of the pressure at sea level. At such high altitudes, low air pressure makes it hard to breathe and is dangerous to human health. The pressure of air in the atmosphere allows you to do many things, from sipping through a straw to simply breathing (see Figure 15.7). When you first suck on a straw, you remove air from the straw, so the air pressure in the straw is lower than For more examples of how we use air pressure, watch the video at this URL: MEDIA Click image to the left or use the URL below. URL: | text | null |
L_0730 | pressure of fluids | T_3619 | Some of the earliest scientific research on fluids was conducted by a French mathematician and physicist named Blaise Pascal (16231662). Pascal was a brilliant thinker. While still a teen, he derived an important theorem in mathematics and also invented a mechanical calculator. One of Pascals contributions to our understanding of fluids is known as Pascals law. | text | null |
L_0730 | pressure of fluids | T_3620 | Pascals law states that a change in pressure at any point in an enclosed fluid is transmitted equally throughout the fluid. A simple example may help you understand Pascals law. Assume you have a small packet of ketchup, like the one in Figure 15.8. If you open one end of the packet and then apply pressure to the other end, what will happen? Ketchup will squirt out the open end. The pressure you exert on the packet is transmitted throughout the ketchup. When the pressure reaches the open end, it forces ketchup out of the packet. To see a video about Pascals law, go to this URL: (2:59). MEDIA Click image to the left or use the URL below. URL: The ability of fluids to transmit pressure in this way can be very useful besides providing ketchup for your French fries! For example, the hydraulic car lift in Figure 15.9 contains fluid that transmits pressure and raises a car so a mechanic can work on it from below. The fluid used, usually a type of oil, cant be compressed. Force is placed on the fluid in a narrow cylinder, and the fluid transmits the pressure throughout the hydraulic system. When the pressure reaches the fluid in the wide cylinder, it forces the cylinder upward, along with the car. The force applied to the car is much greater than the force applied to the fluid in the narrow cylinder. Why? When pressure acts over a wider area, it creates a larger force. Thats because force equals pressure multiplied by the area over which it acts, as you saw above in the equation Force = Pressure Area. Besides hydraulic car lifts, other equipment that uses hydraulic fluid to increase force ranges from brakes to bull- dozers. Even the controls in airplanes use hydraulics. Because of the force-multiplying effect, a flick of a switch can raise or lower heavy wing flaps or landing gear. You can see animations of hydraulic systems at these URLs: http://science.howstuffworks.com/transport/engines-equipment/hydraulic1.htm http://home.wxs.nl/~brink494/hydr_e.htm | text | null |
L_0730 | pressure of fluids | T_3620 | Pascals law states that a change in pressure at any point in an enclosed fluid is transmitted equally throughout the fluid. A simple example may help you understand Pascals law. Assume you have a small packet of ketchup, like the one in Figure 15.8. If you open one end of the packet and then apply pressure to the other end, what will happen? Ketchup will squirt out the open end. The pressure you exert on the packet is transmitted throughout the ketchup. When the pressure reaches the open end, it forces ketchup out of the packet. To see a video about Pascals law, go to this URL: (2:59). MEDIA Click image to the left or use the URL below. URL: The ability of fluids to transmit pressure in this way can be very useful besides providing ketchup for your French fries! For example, the hydraulic car lift in Figure 15.9 contains fluid that transmits pressure and raises a car so a mechanic can work on it from below. The fluid used, usually a type of oil, cant be compressed. Force is placed on the fluid in a narrow cylinder, and the fluid transmits the pressure throughout the hydraulic system. When the pressure reaches the fluid in the wide cylinder, it forces the cylinder upward, along with the car. The force applied to the car is much greater than the force applied to the fluid in the narrow cylinder. Why? When pressure acts over a wider area, it creates a larger force. Thats because force equals pressure multiplied by the area over which it acts, as you saw above in the equation Force = Pressure Area. Besides hydraulic car lifts, other equipment that uses hydraulic fluid to increase force ranges from brakes to bull- dozers. Even the controls in airplanes use hydraulics. Because of the force-multiplying effect, a flick of a switch can raise or lower heavy wing flaps or landing gear. You can see animations of hydraulic systems at these URLs: http://science.howstuffworks.com/transport/engines-equipment/hydraulic1.htm http://home.wxs.nl/~brink494/hydr_e.htm | text | null |
L_0730 | pressure of fluids | T_3621 | Another important law about pressure in fluids was described by Daniel Bernoulli, a Swiss mathematician who lived during the 1700s. Bernoulli used mathematics to arrive at his law. Bernoullis law states that pressure in a moving fluid is less when the fluid is moving faster. For an animation of this law, go to the URL below. Bernoullis law explains how the wings of both airplanes and birds create lift that allows flight (see Figure 15.10). The shape of the wings causes air to flow more quickly and air pressure to be lower above the wings than below them. This allows the wings to lift the plane or bird above the ground against the pull of gravity. A spoiler on a race car, like the one in Figure 15.10, works in the opposite way. Its shape causes air to flow more slowly and air pressure to be greater above the spoiler than below it. As a result, air pressure pushes the car downward, giving its wheels better traction on the track. | text | null |
L_0730 | pressure of fluids | T_3622 | Northern California has a storied, 500-year history of sailing. But despite this rich heritage, scientists and boat designers continue to learn more each day about what makes a sail boat move. Contrary to what you might expect, the physics of sailing still present some mysteries to modern sailors. For more information on the physics of sailing, see http://science.kqed.org/quest/video/the-physics-of-sailing/ . MEDIA Click image to the left or use the URL below. URL: | text | null |
L_0745 | scientific investigation | T_3737 | Scientists investigate the world in many ways. In different fields of science, researchers may use different methods and be guided by different theories and hypotheses. However, most scientists, including physical scientists, usually follow the general approach shown in Figure 2.1. This approach typically includes the following steps: Identify a research question or problem. Form a hypothesis. Gather evidence, or data, to test the hypothesis. Analyze the evidence. Decide whether the evidence supports the hypothesis Draw conclusions. Communicate the results. Scientists may follow these steps in a different sequence. Or they may skip or repeat some of the steps. Which steps are repeated in Figure 2.1? | text | null |
L_0745 | scientific investigation | T_3738 | A scientific investigation begins with a question or problem. Often, the question arises because a scientist is curious about something she has observed. An observation is any information that is gathered with the senses. People often have questions about things they see, hear, or observe in other ways. For example, a teen named Tara has a bracelet with a magnetic clasp, like the one shown in Figure 2.2. Tara has noticed that the two magnets in the clasp feel harder to pull apart on cold days than on warm days. She wonders whether temperature affects the strength of a magnet. | text | null |
L_0745 | scientific investigation | T_3739 | Tara is curious. She decides to investigate. She begins by forming a hypothesis. A hypothesis is a potential answer to a question that can be tested by gathering information. If it isnt possible to gather evidence to test an answer, then it cannot be used as a scientific hypothesis. In fact, the question it addresses may not even be answerable by science. For example, in the childrens television show Sesame Street, there was a large Snuffalufagus (kind of like an elephant). But Snuffy would disappear whenever people came around. So if someone said "Is there a Snuffy on Sesame Street?," that question would be unanswerable by science, since there isnt any test that can be performed because Snuffy would disappear as soon as a scientist showed up. Can you think of other examples of questions outside the realm of science? This important distinction, that evidence taken in by observation is experimented on by a scientist, is what separates legitimate science from other things which may pretend to be science. Fields which claim to be scientific but dont use the scientific method are called "pseudoscience." If a person cant gather data through some sort of instrument or sense information, they cant form a scientific conclusion. If there is no way to prove the hypothesis false, there is no scientific claim either. For example, if a friend told you that Snuffy visited him every day, but he was invisible whenever anyone walked into the room, this claim is not scientific, since there is no way to prove him false. Developing a hypothesis may require creativity as well as reason. However, in Taras case, the hypothesis is simple. She hypothesizes that a magnet is stronger at lower temperatures. Based on her hypothesis, Tara makes a prediction. If she cools a magnet, then it will pick up more metal objects, such as paper clips. Predictions are often phrased as "if-then" statements like this one. Is Taras prediction correct? She decides to do an experiment. | text | null |
L_0745 | scientific investigation | T_3740 | An experiment is a controlled scientific study of specific variables. A variable is a factor that can take on different values. There must be at least two variables in an experiment. They are called the manipulated variable and the responding variable. The manipulated variable (also called the "independent variable") is a factor that is changed by the re- searcher. For example, Tara will change the temperature of a magnet. Temperature is the manipulated variable in her experiment. The responding variable (also called the "dependent variable") is a factor that the researcher predicts will change if the manipulated variable changes. Tara predicts the number of paper clips attracted by the magnet will be greater at lower temperatures. Number of paper clips is the responding variable in her experiment. Tara wonders what other variables might affect the strength of a magnet. She thinks that the size and shape of a magnet might affect its strength. These are variables that must be controlled. A control is a variable that is held constant so it wont influence the outcome of an experiment. By using the same magnet at different temperatures, Tara is controlling for any magnet variables that might affect the results. What other variables should Tara control? (Hint: What about the paper clips?) | text | null |
L_0745 | scientific investigation | T_3740 | An experiment is a controlled scientific study of specific variables. A variable is a factor that can take on different values. There must be at least two variables in an experiment. They are called the manipulated variable and the responding variable. The manipulated variable (also called the "independent variable") is a factor that is changed by the re- searcher. For example, Tara will change the temperature of a magnet. Temperature is the manipulated variable in her experiment. The responding variable (also called the "dependent variable") is a factor that the researcher predicts will change if the manipulated variable changes. Tara predicts the number of paper clips attracted by the magnet will be greater at lower temperatures. Number of paper clips is the responding variable in her experiment. Tara wonders what other variables might affect the strength of a magnet. She thinks that the size and shape of a magnet might affect its strength. These are variables that must be controlled. A control is a variable that is held constant so it wont influence the outcome of an experiment. By using the same magnet at different temperatures, Tara is controlling for any magnet variables that might affect the results. What other variables should Tara control? (Hint: What about the paper clips?) | text | null |
L_0745 | scientific investigation | T_3741 | Not everything in physical science is as easy to study as magnets and paper clips. Sometimes its not possible or desirable to do experiments. There are some things with which a person simply cannot experiment. A distant star is a good example. Scientists study stars by making observations with telescopes and other devices. Often, its important to investigate a problem in the real world instead of in a lab. Scientists do field studies to gather real-world evidence. You can see an example of a field study in Figure 2.3. | text | null |
L_0745 | scientific investigation | T_3742 | Researchers should always communicate their results. By sharing their results, they may be able to get helpful feedback from other scientists. Reporting on research also lets other scientists repeat the investigation to see whether they get the same results. Getting the same results when an experiment is repeated is called replication. If results can be replicated, it means they are more likely to be correct. Replication of investigations is one way that a hypothesis may eventually become a theory. Scientists can share their results in various ways. For example, they can write articles for peer-reviewed science journals. Peer review means that the work is analyzed by peers, in this case other scientists. This is the best way to ensure that the results are accurate and reported honestly. Another way to share results with other scientists is with presentations at scientific meetings (see Figure 2.4). Creating websites and writing articles for newspapers and magazines are ways to share research with the public. Why might this be important? | text | null |
L_0745 | scientific investigation | T_3743 | Ethics refers to rules for deciding between right and wrong. Ethics is an important issue in science. Scientific research must be guided by ethical rules, including those listed below. The rules help ensure that the research is done safely and the results are reliable. Following the rules furthers both science and society. You can learn more about the role of ethics in science by following the links at this URL: Ethical Rules for Scientific Research Scientific research must be reported honestly. It is wrong and misleading to make up or change research results. Scientific researchers must try to see things as they really are. They should avoid being biased by the results they expect or want to get. Researchers must be careful. They should take pains to avoid errors in their data. Researchers studying human subjects must tell their subjects about any potential risks of the research. Subjects also must be told that they can refuse to participate in the research. Researchers must inform coworkers, students, and members of the community about any risks of the research. They should proceed with the research only if they have the consent of these groups. Researchers studying living animals must treat them humanely. They should provide for their needs and do what they can to avoid harming them (see Figure 2.5). Sometimes, science can help people make ethical decisions in their own lives, although science is unlikely to be the only factor involved. For example, scientific evidence shows that human actions are affecting Earths climate. Actions such as driving cars are causing Earth to get warmer. Does this mean that it is unethical to drive a car to work or school? What if driving is the only way to get there? As this example shows, ethical decisions are likely to be influenced by many factors, not just science. Can you think of other factors that might affect ethical decisions such as this one? | text | null |
L_0746 | science skills | T_3744 | One of the most important aspects of measuring is the system of units used for measurement. Remember the Mars Climate Orbiter that opened this chapter? It shows clearly why a single system of measurement units is needed in science. | text | null |
L_0746 | science skills | T_3745 | The measurement system used by most scientists is the International System of Units, or SI. Table 2.2 lists common units in this system. SI is easy to use because everything is based on the number 10. Basic units are multiplied or divided by powers of ten to arrive at bigger or smaller units. Prefixes are added to the names of the basic units to indicate the powers of ten. For example, the meter is the basic unit of length. The prefix kilo- means 1000, so a kilometer is 1000 meters. Can you infer what the other prefixes in the table mean? If not, you can find out at this URL: http://physics.nist.gov/cuu/Units/prefixes.html . Variable Length Volume Mass Basic SI Unit (English Equivalent) meter (m) (1 m = 39.37 in) cubic meter (m3 ) (1 m3 = 1.3 yd3 ) gram (g) (1 g = 0.04 oz) Related SI Units Equivalent Units kilometer (km) decimeter (dm) centimeter (cm) millimeter (mm) micrometer (m) nanometer (nm) liter (L) milliliter (mL) kilogram (kg) milligram (mg) = 1000 m = 0.1 m = 0.01 m = 0.001 m = 0.000001 m = 0.000000001 m = 1 dm3 = 1 cm3 = 1000 g = 0.001 g The SI system has units for other variables in addition to the three shown here in Table 2.2. Some of these other units are introduced in later chapters. Problem Solving Problem: Use information in Table 2.2 to convert 3 meters to inches. Solution: 3 m = 3 39.37 in = 118.11 in You Try It! Problem: Rod needs to buy 1 m of wire for a science experiment. The wire is sold by the yard, not the meter. If he buys 1 yd of wire, will he have enough? (Hint: How many inches are there in 1 yd? In 1 m?) | text | null |
L_0746 | science skills | T_3746 | The SI scale for measuring temperature is the Kelvin scale. However, some scientists use the Celsius scale instead. If you live in the U.S., you are probably more familiar with the Fahrenheit scale. Table 2.3 compares all three temperature scales. What is the difference between the boiling and freezing points of water on each of these scales? Scale Kelvin Celsius Fahrenheit Freezing Point of Water 273 K 0C 32F Boiling Point of Water 373 K 100C 212F Each 1-degree change on the Kelvin scale is equal to a 1-degree change on the Celsius scale. This makes it easy to convert measurements between Kelvin and Celsius. For example, to go from Celsius to Kelvin, just add 273. How would you convert a temperature from Kelvin to Celsius? Converting between Celsius and Fahrenheit is more complicated. The following conversion factors are used: Celsius ! Fahrenheit : ( C 1.8) + 32 = F Fahrenheit ! Celsius : ( F 32) 1.8 = C Problem Solving Problem: Convert 10C to Fahrenheit. Solution: (10C 1.8) + 32 = 50F You Try It! Problem: The weather forecaster predicts a high temperature today of 86F. What will the temperature be in Celsius? | text | null |
L_0746 | science skills | T_3747 | Measuring devices must be used correctly to get accurate measurements. Figure 2.6 shows the correct way to use a graduated cylinder to measure the volume of a liquid. Follow these steps when using a graduated cylinder to measure liquids: Place the cylinder on a level surface before adding liquid. Move so your eyes are at the same level as the top of the liquid in the cylinder. Read the mark on the glass that is at the lowest point of the curved surface of the liquid. This is called the meniscus. At the URLs below, you can see the correct way to use a metric ruler to measure length and a beam balance to measure mass. (beam balance) (5:14) | text | null |
L_0746 | science skills | T_3748 | Measurements should be both accurate and precise. Accuracy is how close a measurement is to the true value. For example, 66 mL is a fairly accurate measure- ment of the liquid in Figure 2.6. Precision is how exact a measurement is. A measurement of 65.5 mL is more precise than a measurement of 66 mL. But in Figure 2.6, it is not as accurate. You can think of accuracy and precision in terms of a game like darts. If you are aiming for the bulls-eye and get all of the darts close to it, you are being both accurate and precise. If you get the darts all close to each other somewhere else on the board, you are precise, but not accurate. And finally, if you get the darts spread out all over the board, you are neither accurate nor precise. | text | null |
L_0746 | science skills | T_3749 | Record keeping is very important in scientific investigations. Follow the tips below to keep good science records. Use a bound laboratory notebook so pages will not be lost. Write in ink for a permanent record. Record the steps of all procedures. Record all measurements and observations. Use drawings as needed. Date all entries, including drawings. | text | null |
L_0746 | science skills | T_3750 | Doing science often requires calculations. Converting units is just one example. Calculations are also needed to find derived quantities. | text | null |
L_0746 | science skills | T_3751 | Derived quantities are quantities that are calculated from two or more different measurements. Examples include area and volume. Its easy to calculate these quantities for a simple shape. For a rectangular solid, like the one in Figure 2.7, the formulas are: Area (of each side) = length width (l w) Volume = length width height (l w h) Helpful Hints When calculating area and volume, make sure that: all the measurements have the same units. answers have the correct units. Area should be in squared units, such as cm2 ; volume should be in cubed units, such as cm3 . Can you explain why? Naturally, not all derived quantities will have the same types of units. In the examples above, the only fundamental unit used was meters for the length of one of the sides of the box. However, if you had a quantity like speed (a derived quantity), it would be equal to distance traveled (which is meters) divided by the amount of time you spent traveling that distance (which is in seconds). Therefore your speed would be measured in meters per second. | text | null |
L_0746 | science skills | T_3752 | Assume you are finding the area of a rectangle with a length of 6.8 m and a width of 6.9 m. When you multiply the length by the width on your calculator, the answer you get is 46.92 m2 . Is this the correct answer? No; the correct answer is 46.9 m2 . The correct answer must be rounded down so there is just one digit to the right of the decimal point. Thats because the answer cannot have more digits to the right of the decimal point than any of the original measurements. Using extra digits implies a greater degree of precision than actually exists. The correct number of digits is called the number of significant figures. To learn more about significant figures and rounding, you can watch the videos at the URLs below. (3:20) (8:30) | text | null |
L_0746 | science skills | T_3753 | Quantities in science may be very large or very small. This usually requires many zeroes to the left or right of the decimal point. Such numbers can be hard to read and write accurately. Thats where scientific notation comes in. Scientific notation is a way of writing very large or small numbers that uses exponents. Numbers are written in this format: a 10b The letter a stands for a decimal number. The letter b stands for an exponent, or power, of 10. For example, the number 300 is written as 3.0 102 . The number 0.03 is written as 3.0 10 2 . Figure 2.8 explains how to convert numbers to and from scientific notation. For a review of exponents, watch: You Try It! Problem: Write the number 46,000,000 in scientific notation. | text | null |
L_0746 | science skills | T_3754 | In a scientific investigation, a researcher may make and record many measurements. These may be compiled in spreadsheets or data tables. In this form, it may be hard to see patterns or trends in the data. Descriptive statistics and graphs can help organize the data so patterns and trends are easier to spot. Example: A vehicle checkpoint was set up on a busy street. The number of vehicles of each type that passed by the checkpoint in one hour was counted and recorded in Table 2.4. These are the only types of vehicles that passed the checkpoint during this period. Type of Vehicle 4-door cars 2-door cars SUVs Number 150 50 80 Type of Vehicle vans pick-up trucks Number 50 70 | text | null |
L_0746 | science skills | T_3755 | A descriptive statistic sums up a set of data in a single number. Examples include the mean and range. The mean is the average value. It gives you an idea of the typical measurement. The mean is calculated by summing the individual measurements and dividing the total by the number of measurements. For the data in Table 2.4, the mean number of vehicles by type is: (150 + 50 + 80 + 50 + 70) 5 = 80. (There are two other words people can sometimes use when they use the word "average." They might be referring to a quantity called the "median" or the "mode." Youll see these quantities in later courses, but for now, well just say the average is the same thing as the mean.) The range is the total spread of values. It gives you an idea of the variation in the measurements. The range is calculated by subtracting the smallest value from the largest value. For the data in Table 2.4, the range in numbers of vehicles by type is: 150 - 50 = 100. | text | null |
L_0746 | science skills | T_3756 | Graphs can help you visualize a set of data. Three commonly used types of graphs are bar graphs, circle graphs, and line graphs. Figure 2.9 shows an example of each type of graph. The bar and circle graphs are based on the data in Table 2.4, while the line graph is based on unrelated data. You can see more examples at this URL: Bar graphs are especially useful for comparing values for different types of things. The bar graph in Figure Circle graphs are especially useful for showing percents of a whole. The circle graph in Figure 2.9 shows the percent of all vehicles counted that were of each type. Line graphs are especially useful for showing changes over time. The line graph in Figure 2.9 shows how distance from school changed over time when some students went on a class trip. Helpful Hints Circle graphs show percents of a whole. What are percents? Percents are fractions in which the denominator is 100. Example: 30% = 30/100 Percents can also be expressed as decimal numbers. Example: 30% = 0.30 You Try It! Problem: Show how to calculate the percents in the circle graph in Figure 2.9. Need a refresher on percents, fractions, and decimals? Go to this URL: | text | null |
L_0746 | science skills | T_3757 | Did you ever read a road map, sketch an object, or play with toy trucks or dolls? No doubt, the answer is yes. What do all these activities have in common? They all involve models. A model is a representation of an object, system, or process. For example, a road map is a representation of an actual system of roads on the ground. Models are very useful in science. They provide a way to investigate things that are too small, large, complex, or distant to investigate directly. Figure 2.10 shows an example of a model in chemistry. To be useful, a model must closely represent the real thing in important ways, but it must be simpler and easier to manipulate than the real thing. Do you think the model in Figure 2.10 meets these criteria? | text | null |
L_0746 | science skills | T_3758 | Research in physical science can be exciting, but it also has potential dangers. Whether in the lab or in the field, knowing how to stay safe is important. | text | null |
L_0746 | science skills | T_3759 | Lab procedures and equipment may be labeled with safety symbols. These symbols warn of specific hazards, such as flames or broken glass. Learn the symbols so you will recognize the dangers. A list of common safety symbols is shown in Figure 2.11. Do you know how to avoid each hazard? You can learn more at this URL: | text | null |
L_0746 | science skills | T_3759 | Lab procedures and equipment may be labeled with safety symbols. These symbols warn of specific hazards, such as flames or broken glass. Learn the symbols so you will recognize the dangers. A list of common safety symbols is shown in Figure 2.11. Do you know how to avoid each hazard? You can learn more at this URL: | text | null |
L_0746 | science skills | T_3760 | Following basic safety rules is the best way to stay safe in science. Safe practices help prevent accidents. Several lab safety rules are listed below. Different rules may apply when you work in the field. But in all cases, you should always follow your teachers instructions. Lab Safety Rules Wear safety gear, including goggles, an apron, and gloves. Wear a long-sleeved shirt and shoes that completely cover your feet. Tie back your hair if it is long. Do not eat or drink in the lab. Never work alone. Never perform unauthorized experiments. Never point the open end of a test tube at yourself or another person. Always add acid to water never water to acid and add the acid slowly. To smell a substance, use your hand to fan vapors toward your nose rather than smell it directly. This is demonstrated in Figure 2.12. When disposing of liquids in the sink, flush them down the drain with lots of water. Wash glassware and counters when you finish your lab work. Thoroughly wash your hands with soap and water before leaving the lab. Even when you follow the rules, accidents can happen. Immediately alert your teacher if an accident occurs. Report all accidents, even if you dont think they are serious. | text | null |
L_0747 | technology | T_3761 | Technology is the application of knowledge to real-world problems. It includes methods and processes as well as devices like computers and cars. An example is the Bessemer process. It is a cheap method of making steel that was invented in the 1850s. It is just one of many technological advances that have occurred in manufacturing. Technology is also responsible for most of the major advances in agriculture, transportation, communications, and medicine. Clearly, technology has had a huge impact on people and society. It is hard to imagine what life would be like without it. Professionals in technology are generally called engineers. Most engineers have a strong background in physical science. There are many different careers in engineering. You can learn about some of them at the URLs below. | text | null |
L_0747 | technology | T_3762 | The development of new technology is called technological design. It is similar to scientific investigation. Both processes use evidence and logic to solve problems. | text | null |
L_0747 | technology | T_3763 | Figure 2.13 shows the steps of the technological design process. Consider the problem of developing a solar- powered car. Many questions would have to be researched in the design process. For example, what is the best shape for gathering the suns rays? How will the energy from the sun be stored? Will a back-up energy source be needed? After researching the answers, possible designs are developed. This takes imagination as well as reason. Then a model is made of the best design, and the model is tested. This allows any problems with the design to be worked out before a final design is selected. | text | null |
L_0747 | technology | T_3764 | Technological design always has constraints. Constraints are limits on the design. Common constraints include: laws of nature, such as the law of gravity. properties of the materials used. cost of producing a technology. Ethical concerns are also constraints on many technological designs. Like scientists, engineers must follow ethical rules. For example, the technologies they design must be as safe as possible for people and the environment. Engineers must weigh the benefits and risks of new technologies, and the benefits should outweigh the risks. | text | null |
L_0747 | technology | T_3765 | Technology advances as new materials and processes are invented. Computers are a good example. Table 2.5 and the videos below show some of the milestones in their evolution. The evolution of modern computers began in the 1930s. Computers are still evolving today. How have computers changed during your lifetime? (4:11) MEDIA Click image to the left or use the URL below. URL: (5:36) MEDIA Click image to the left or use the URL below. URL: Computer (Year) ENIAC (1946) US Army Photo ERMA (1955) Description Like other early computers, the huge ENIAC computer used vacuum tubes for electrical signals. This made it very large and expensive. It could do just one task at a time. It had to be rewired to change programs. Thats what the women in this photo are doing. The ERMA computer represented a new computer technology. It used transistors instead of vacuum tubes. This allowed computers to be smaller, cheaper, and more energy efficient. Computer (Year) PDP-8 (1968) Description By the late 1960s, tiny transistors on silicon chips were invented. They increased the speed and efficiency of computers. They also allowed computers to be much smaller. The PDP-8 computer pictured here was the first "mini" computer. Macintosh 128K (1984) The next major advance in computers was the develop- ment of microprocessors. A microprocessor consisted of thousands of integrated circuits placed on a tiny sili- con chip. This allowed computers to be more powerful and even smaller. The computer pictured here is the first Macintosh personal computer. MacBook Air (2010) The computers of the 21st century are tiny compared with the lumbering giants of the mid-1900s. Their problem-solving abilities are also immense compared with early computers. The diversity of software pro- grams available today allows users to undertake an immense variety of tasks and no rewiring is needed! | text | null |
L_0747 | technology | T_3766 | Technology is sometimes referred to as applied science, but it has a different goal than science. The goal of science is to increase knowledge. The goal of technology is to use knowledge for practical purposes. Although they have different goals, technology and science work hand in hand. Each helps the other advance. Scientific knowledge is needed to create new technologies. New technologies are used to further science. The microscope is a good example. Scientific knowledge of light allowed 17th century lens makers to make the first microscopes. This new technology let scientists view a world of tiny objects they had never before seen. Figure | text | null |
L_0747 | technology | T_3767 | Whats 100,000 times thinner than a strand of hair? A nanometer. Discover the nanotech boom in Berkeley, where researchers are working to unlock the potential of nanoscience to battle global warming and disease. For more information on nanotechnology, see http://science.kqed.org/quest/video/nanotechnology-takes-off/ . MEDIA Click image to the left or use the URL below. URL: | text | null |
L_0747 | technology | T_3768 | The goal of technology is to solve peoples problems. Therefore, the problems of society generally set the direction that technology takes. Technology, in turn, affects society. It may make peoples lives easier or healthier. Two examples are described in Figure 2.15. You can read about other examples at these URLs: http://mezocore.wordpress.com/ | text | null |
L_0747 | technology | T_3769 | Everyday, women living in the refugee camps of Darfur, Sudan must walk for up to seven hours outside the safety of the camps to collect firewood for cooking, putting them at risk for violent attacks. Now, researchers at Lawrence Berkeley National Laboratory have engineered a more efficient wood-burning stove, which is greatly reducing both the womens need for firewood and the threats against them. For more information on these stoves, see http://scien MEDIA Click image to the left or use the URL below. URL: | text | null |
L_0770 | behavior of gases | T_3945 | Pressure is defined as the amount of force pushing against a given area. How much pressure a gas exerts depends on the amount of gas. The more gas particles there are, the greater the pressure. You usually cannot feel it, but air has pressure. The gases in Earths atmosphere exert pressure against everything they contact. The atmosphere rises high above Earths surface. It contains a huge number of individual gas particles. As a result, the pressure of the tower of air above a given spot on Earths surface is substantial. If you were standing at sea level, the amount of force would be equal to 10.14 newtons per square centimeter (14.7 pounds per square inch). This is illustrated in Figure 4.11. | text | null |
L_0770 | behavior of gases | T_3946 | For a given amount of gas, scientists have discovered that the pressure, volume, and temperature of a gas are related in certain ways. Because these relationships always hold in nature, they are called laws. The laws are named for the scientists that discovered them. | text | null |
L_0770 | behavior of gases | T_3947 | Boyles law was discovered in the 1600s by an Irish chemist named Robert Boyle. According to Boyles law, if the temperature of a gas is held constant, increasing the volume of the gas decreases its pressure. Why is this the case? As the volume of a gas increases, its particles have more room to spread out. This means that there are fewer particles bumping into any given area. This decreases the pressure of the gas. The graph in Figure 4.12 shows this relationship between volume and pressure. Because pressure and volume change in opposite directions, their relationship is called an inverse relationship. You can see an animation of the relationship at this URL: A scuba diver, like the one in Figure 4.13, releases air bubbles when he breathes under water. As he gets closer to the surface of the water, the air bubbles get bigger. Boyles law explains why. The pressure of the water decreases as the diver gets closer to the surface. Because the bubbles are under less pressure, they increase in volume even though the amount of gas in the bubbles remains the same. | text | null |
L_0770 | behavior of gases | T_3947 | Boyles law was discovered in the 1600s by an Irish chemist named Robert Boyle. According to Boyles law, if the temperature of a gas is held constant, increasing the volume of the gas decreases its pressure. Why is this the case? As the volume of a gas increases, its particles have more room to spread out. This means that there are fewer particles bumping into any given area. This decreases the pressure of the gas. The graph in Figure 4.12 shows this relationship between volume and pressure. Because pressure and volume change in opposite directions, their relationship is called an inverse relationship. You can see an animation of the relationship at this URL: A scuba diver, like the one in Figure 4.13, releases air bubbles when he breathes under water. As he gets closer to the surface of the water, the air bubbles get bigger. Boyles law explains why. The pressure of the water decreases as the diver gets closer to the surface. Because the bubbles are under less pressure, they increase in volume even though the amount of gas in the bubbles remains the same. | text | null |
L_0770 | behavior of gases | T_3948 | Charless law was discovered in the 1700s by a French physicist named Jacques Charles. According to Charless law, if the pressure of a gas is held constant, increasing the temperature of the gas increases its volume. What happens when a gas is heated? Its particles gain energy. With more energy, the particles have a greater speed. Therefore, they can move more and spread out farther. The volume of the gas increases as it expands and takes up more space. The graph in Figure 4.14 shows this relationship between the temperature and volume of a gas. You can see an animation of the relationship at this URL: . Roger had a latex balloon full of air inside his air-conditioned house. When he took the balloon outside in the hot sun, it got bigger and bigger until it popped. Charless law explains why. As the gas in the balloon warmed in the sun, its volume increased. It stretched and expanded the latex of the balloon until the balloon burst. | text | null |
L_0770 | behavior of gases | T_3949 | Amontons law was discovered in the late 1600s by a French physicist named Guillaume Amonton. According to Amontons law, if the volume of a gas is held constant, increasing the temperature of the gas increases its pressure. Why is this the case? A heated gas has more energy. Its particles move more and have more collisions, so the pressure of the gas increases. The graph in Figure 4.15 shows this relationship. A woman checked the air pressure in her tires before driving her car on a cold day (see Figure 4.16). The tire pressure gauge registered 29 pounds of pressure per square inch. After driving the car several miles on the highway, the woman stopped and checked the tire pressure again. This time the gauge registered 32 pounds per square inch. Amontons law explains what happened. As the tires rolled over the road, they got warmer. The air inside the tires also warmed. As it did, its pressure increased. | text | null |
L_0770 | behavior of gases | T_3949 | Amontons law was discovered in the late 1600s by a French physicist named Guillaume Amonton. According to Amontons law, if the volume of a gas is held constant, increasing the temperature of the gas increases its pressure. Why is this the case? A heated gas has more energy. Its particles move more and have more collisions, so the pressure of the gas increases. The graph in Figure 4.15 shows this relationship. A woman checked the air pressure in her tires before driving her car on a cold day (see Figure 4.16). The tire pressure gauge registered 29 pounds of pressure per square inch. After driving the car several miles on the highway, the woman stopped and checked the tire pressure again. This time the gauge registered 32 pounds per square inch. Amontons law explains what happened. As the tires rolled over the road, they got warmer. The air inside the tires also warmed. As it did, its pressure increased. | text | null |
L_0795 | air pressure and altitude | T_4113 | Because gas particles in the airlike particles of all fluidsare constantly moving and bumping into things, they exert pressure. The pressure exerted by the air in the atmosphere is greater close to Earths surface and decreases as you go higher above the surface. You can see this in the Figure 1.1. Q: Denver, Colorado, is called the mile-high city because it is located 1 mile (1.6 km) above sea level. What is the average atmospheric pressure that high above sea level? A: From the Figure 1.1, the average atmospheric pressure 1.6 km above sea level is about 85 kPa. | text | null |
L_0795 | air pressure and altitude | T_4114 | There are two reasons why air pressure decreases as altitude increases: density and depth of the atmosphere. Most gas molecules in the atmosphere are pulled close to Earths surface by gravity, so gas particles are denser near the surface. With more gas particles in a given volume, there are more collisions of particles and therefore greater pressure. The depth (distance from top to bottom) of the atmosphere is greatest at sea level and decreases at higher altitudes. With greater depth of the atmosphere, more air is pressing down from above. Therefore, air pressure is greatest at sea level and falls with increasing altitude. On top of Mount Everest, which is the tallest mountain on Earth, air pressure is only about one-third of the pressure at sea level. | text | null |
L_0795 | air pressure and altitude | T_4115 | The pressure of air in the atmosphere allows us to do many things, from sipping through a straw to simply breathing. You can see in the Figures 1.2 and 1.3 how we use air pressure in both of these ways. When you first suck on a straw, you remove air from the straw, so the air pressure in the straw is lower that the air pressure on the surface of the drink. A fluid always flows from an area of higher pressure to an area of lower pressure, so the drink moves up the straw and into your mouth. | text | null |
L_0795 | air pressure and altitude | T_4115 | The pressure of air in the atmosphere allows us to do many things, from sipping through a straw to simply breathing. You can see in the Figures 1.2 and 1.3 how we use air pressure in both of these ways. When you first suck on a straw, you remove air from the straw, so the air pressure in the straw is lower that the air pressure on the surface of the drink. A fluid always flows from an area of higher pressure to an area of lower pressure, so the drink moves up the straw and into your mouth. | text | null |
L_0799 | amontonss law | T_4125 | There was no additional air in the tire the second time Lawrence checked the air pressure, but something did change between the two measurements. The tires had rolled over 10 miles of road on the trip to school. Any time one surface moves over another, it causes friction. Friction is a force that opposes the motion of two surfaces that are touching, and friction between two surfaces always generates heat. Quickly rub your hands together and youll feel the heat generated by the friction between them. As the tires moved over the road, friction between the tires and road generated heat. In short, the tires got warmer and so did the air inside them. | text | null |
L_0799 | amontonss law | T_4126 | The space inside a car tire is more-or-less fixed, so it has a constant volume. What happens when the volume of air is constant and its temperature increases? Lawrence found out the answer to that question when he measured the air pressure in his tire. Increasing the temperature of a gas such as air, while holding its volume constant, increases the pressure of the gas. This relationship between temperature and pressure of a gas is called Amontons law. It was first proposed by a French scientist named Guillaume Amontons in the late 1600s. Amontons gas law is just one of three commonly known gas laws. The other two are Boyles law and Charles law. Q: How does Amontons gas law explain the difference in air pressure in Lawrences tire? A: The tireand the air inside itgot warmer because of friction with the road. The volume of air inside the tire was more-or-less constant, so the pressure of the air increased when it got warmer. | text | null |
L_0799 | amontonss law | T_4127 | Why does the pressure of a gas increase as it gets warmer? Particles of a gas are constantly moving and bumping into things. The force of the collisions is measured by pressure. Pressure is the amount of force exerted on a given area, such as pounds of force per square inch. When gas particles heat up and gain energy, they move faster. This causes more collisions and greater pressure. Therefore, heating particles of gas in a closed space causes the pressure of the gas to increase. | text | null |
L_0807 | bernoullis law | T_4156 | Bernoullis law states that the pressure of a moving fluid such as air is less when the fluid is moving faster. Pressure is the amount of force applied per given area. The law is named for Daniel Bernoulli, a Swiss mathematician who discovered it during the 1700s. Bernoulli used mathematics to arrive at his law. | text | null |
L_0807 | bernoullis law | T_4157 | Did you ever wonder how the wings of airplanes or birds allow them to fly? Bernoullis law provides the answer. Look at the wings of the plane and hawk in the Figure 1.1. The shape of the wings causes air to flow more slowly below them than above them. This causes air pressure to be greater below the wings than above them. The difference in air pressure lifts the plane or bird above the ground. Q: How does a spoiler on a racecar use Bernoullis law? A: A spoiler on a racecar is like an upside-down wing. Its shape causes air to flow more slowlyand air pressure to be greaterabove the spoiler than below it. As a result, air pressure pushes the car downward, helping it to stay on the track. | text | null |
L_0814 | boyles law | T_4178 | What does popping bubble wrap have to do with science? Actually, it demonstrates an important scientific law, called Boyles law. Like other laws in science, this law describes what always happens under certain conditions. Boyles law is one of three well-known gas laws, which state the relationships among temperature, volume, and pressure of gases. (The other two gas laws are Charles law and Amontons law.) According to Boyles law, if the temperature of a gas is held constant, then decreasing the volume of the gas increases its pressureand vice versa. Thats what happens when you squeeze the bubbles of bubble wrap. You decrease the bubbles volume, so the air pressure inside the bubbles increases until they pop. | text | null |
L_0814 | boyles law | T_4179 | Boyles law is named for Robert Boyle, the English scientist who discovered this relationship between gas volume and pressure. Boyle based the law on his own controlled experiments. He published his results, along with detailed descriptions of his procedures and observations, in the 1660s. These steps were unheard of in his day. Mainly because of his careful research and the details he provided about it, Boyle has been called the father of modern chemistry. | text | null |
L_0814 | boyles law | T_4180 | Imagine a container of gas molecules like the one in the Figure 1.1. The container in the sketch has a lid that can be pushed down to shrink the volume of the gas inside. Notice what happens as the lid is lowered. The gas molecules crowd closer together because there is less space for them to occupy and they have nowhere else to go. Gas molecules have a lot of energy. They are always moving and bouncing off each other and anything else in their path. When gas molecules bump into things, it creates pressure. Pressure is greater when gas molecules occupy a smaller space, because the greater crowding results in more collisions. In other words, decreasing the volume of a gas increases its pressure. | text | null |
L_0814 | boyles law | T_4181 | As the volume of gas in the container pictured in the Figure 1.1 gets smaller, the pressure of the gas molecules becomes greater. When two variables change in opposite directions like this, the variables have an inverse, or upside-down, relationship. Q: How could you show an inverse relationship with a graph? Sketch a graph to show what the relationship between gas volume and pressure might look like. Let the x-axis represent volume (V) and the y-axis represent pressure (P). A: Did you sketch a graph like the one in the Figure 1.2? Lets see why this graph is correct. Find the point on the line where volume is smallest. Thats were pressure is highest. Then find the point where volume is largest. Thats where pressure is lowest. Whenever you see a graph with this shape, it usually represents variables that have an inverse relationship, like gas volume and pressure. | text | null |
L_0826 | charless law | T_4217 | The popularity of hot air balloons got scientists thinking about gases and what happens to them when they heat up. In the early 1800s, two French scientistsJacques Charles and Joseph Gay-Lussacdecided to investigate how changes in the temperature of a gas affect the amount of space it takes up, or its volume. They heated air and measured how its volume changed. The two scientists already knew that the pressure of a gas affects it volume. This had been demonstrated back in the 1660s by the English scientist Robert Boyle. So Charles and Gay-Lussac controlled the effects of pressure by keeping it constant in their experiments. Based on the results of the research, Charles developed a scientific law about gases. It is one of three well-known gas laws, the others being Boyles law and Amontons law. According to Charless law, when the pressure of a gas is held constant, increasing its temperature increases its volume. The opposite is also true: decreasing the temperature of a gas decreases it volume. | text | null |
L_0839 | communication in science | T_4256 | The last step of most scientific investigations is reporting the results. When scientists communicate their findings, they add to the body of scientific knowledge, and thats how science advances. Science generally builds on previous knowledge, sometimes advancing in giant steps but more often in baby steps. The brick building analogy in the Figure 1.1 may help you better understand why communication is important in science. When scientists communicate about their research, they may also get useful feedback from other scientists. For example, comments from other scientists might help them improve their research design or interpret their findings in a different way. Other scientists can also repeat the research to see if they get the same results. Q: Why might it be important for other scientists to repeat an investigation? A: If an investigation is repeated and different results are obtained, then it throws doubt on the original research. On the other hand, if the same results are obtained, scientists can place more confidence in them. | text | null |
L_0839 | communication in science | T_4257 | The posters shown in the opening image are just one of several ways that scientists may communicate about their research. Some of the most common ways scientists communicate are listed below. You can think of scientific knowledge as a brick building, and the work of a single sci- entist as an individual brick. Considered by itself, the work of a single scientist may not seem that important, yet it may be an important piece of the overall structure. But unless a scientist communicates re- search results, that single brick may never be added to the building. Scientists may present papers about their research at scientific conferences. This is a good way to quickly reach an audience of other scientists who are most interested in the research topic. Scientists may publish articles about their research in peer-reviewed science journals. Peer review means that the work is analyzed by peers, in other words, by other scientists. The articles are published only if the other scientists are convinced that the research is accurate and honest. Scientists may testify about their research before congress if their findings relate to matters of public policy, such as environmental pollution. Scientists may communicate about their research to the general public. For example, they might create a Web site about their research, blog about it, or write articles for newspapers or magazines. Q: Why might it be important for scientists to communicate about their research to the general public? Give an example. A: Communicating to the general public might be important if the research is directly related to peoples lives. For example, assume that a scientist has investigated how driving habits are related to car crashes. She might write a newspaper article to share the research results with the public so they can adopt driving habits that reduce the risk of crashes. | text | null |
L_0895 | ethics in science | T_4429 | Ethics refers to deciding whats right and whats wrong. Making ethical decisions involves weighing right and wrong in order to make the best choice. The ethical problem of the Pacific yew has both right and wrong aspects. Its right to save lives with the cancer drug that comes from the tree bark, but its wrong to endanger the tree and risk its extinction. Q: What do you think is the most ethical decision about the Pacific yew? Should the bark be used to make the drug and possibly save human lives? Or should this be prohibited in order to protect the tree from possible extinction? A: This is tough ethical dilemma, and there is no right or wrong answer. Ethical dilemmas such as this often spur scientists to come up with new solutions to problems. Thats what happened in the case of the Pacific yew. Scientists tackled and solved the problem of determining the chemical structure of the anti-cancer drug so it could be synthesized in labs. This is a win-win solution to the problem. The synthetic drug is now available to save lives, and the trees are no longer endangered by being stripped of their bark. | text | null |
L_0895 | ethics in science | T_4430 | Ethics is an important consideration in science. Scientific investigations must be guided by what is right and what is wrong. Thats where ethical rules come in. They help ensure that science is done safely and that scientific knowledge is reliable. Here are some of the ethical rules that scientists must follow: Scientific research must be reported honestly. It is wrong and misleading to make up or change research results. Scientific researchers must try to see things as they really are. They should avoid being biased by the results they expect or hope to get. Researchers must be careful. They should do whatever they can to avoid errors in their data. Researchers must inform coworkers and members of the community about any risks of their research. They should do the research only if they have the consent of these groups. Researchers studying living animals must treat them humanely. They should provide for their needs and take pains to avoid harming them. Researchers studying human subjects must tell their subjects that they have the right to refuse to participate in the research. Human subjects also must be fully informed about their role in the research, including any potential risks. You can read about a terrible violation of this ethical rule in the Figure 1.1. | text | null |
L_0895 | ethics in science | T_4431 | Sometimes, science can help people make ethical decisions in their own lives. For example, scientific evidence shows that certain human actionssuch as driving cars that burn gasolineare contributing to changes in Earths climate. This, in turn, is causing more severe weather and the extinction of many species. A number of ethical decisions might be influenced by this scientific knowledge. Q: For example, should people avoid driving cars to work or school because it contributes to climate change and the serious problems associated with it? What if driving is the only way to get there? Can you think of an ethical solution? A: This example shows that ethical decisions may not be all or nothing. For example, rather than driving alone, people might carpool with others. This would reduce their impact on climate change. They could also try to reduce their impact in other ways. For example, they might turn down their thermostat in cold weather so their furnace burns less fuel. | text | null |
L_0900 | field study | T_4443 | Although experiments are the gold standard for scientific investigations, sometimes its not possible or desirable to do experiments. Often its important to investigate a problem in the real world instead of in a lab. An investigation that gathers evidence in the real worldas the environmental chemist above is doingis called a field study. Q: Why are field studies important for environmental scientists? A: To learn about the environment, scientists need to take measurements and make observations in the real world. This means gathering evidence in field studies; collecting samples of water from a river is one example of this method. | text | null |
L_0900 | field study | T_4444 | The environmental scientist above will gather samples of river water in several different locations. Then he will take the samples back to a lab to analyze them. He will do tests to identify any pollutants in the samples. Taking samples from different locations may help him identify the source of any pollution he finds. Pollution can enter a river from a single source, such as a waste water pipe from a factory. This is called point-source pollution. Or pollution can enter a river in runoff rainwater that picks up pollutants as it runs over the ground. This type of pollution enters the river everywhere. This is called nonpoint-source pollution. Q: Assume that the river is polluted only by nonpoint-source pollution. Describe how the samples of river water would compare in terms of the pollutants they contain. A: All of the samples would contain about the same amount and types of pollutants. Q: How might point-source pollution be identified? A: Just one sample might be polluted. This would be the sample taken at, or just downstream from, the single source of pollution. | text | null |
L_0909 | gases | T_4469 | A gas is one of four well-known states of matter. (The other three are solid, liquid, and plasma). The particles of a gas can pull apart from each other and spread out. As a result, a gas does not have a fixed shape or a fixed volume. In fact, a gas always spreads out to take up whatever space is available to it. If a gas is enclosed in a container, it spreads out until it has the same volume as the container. Q: The sketches in the Figure 1.1 represent two identical sealed boxes that contain only air particles (represented by dots). There are more air particles in box B than box A. Which box contains a greater volume of air? A: This is a trick question! The air inside each box expands to fill the available space, which is identical for both boxes. There are more air particles in box B, but the volume of air is exactly the same in both boxes. | text | null |
L_0909 | gases | T_4470 | Particles of gas are constantly moving in all directions at random. As a result, they are always bumping into each other and other things. This is modeled in the Figure 1.2. The force of the particles against things they bump into creates pressure. Pressure is defined in physics as the amount of force pushing against a given area. How much pressure a gas exerts depends on the number of gas particles in a given space and how fast they are moving. The more gas particles there are and the faster they are moving, the greater the pressure they create. The arrows show that particles of a gas move randomly in all directions. Q: Look at box A and box B in the previous question. Is air pressure the same in both boxes? Why or why not? A: Air pressure is greater in box B. Thats because there are more air particles in box B to bump into each other and into the sides of the container. Therefore, the particles in box B exert more force on a given area. | text | null |
L_0909 | gases | T_4470 | Particles of gas are constantly moving in all directions at random. As a result, they are always bumping into each other and other things. This is modeled in the Figure 1.2. The force of the particles against things they bump into creates pressure. Pressure is defined in physics as the amount of force pushing against a given area. How much pressure a gas exerts depends on the number of gas particles in a given space and how fast they are moving. The more gas particles there are and the faster they are moving, the greater the pressure they create. The arrows show that particles of a gas move randomly in all directions. Q: Look at box A and box B in the previous question. Is air pressure the same in both boxes? Why or why not? A: Air pressure is greater in box B. Thats because there are more air particles in box B to bump into each other and into the sides of the container. Therefore, the particles in box B exert more force on a given area. | text | null |
L_0909 | gases | T_4471 | We live in a sea of air called the atmosphere. Can you feel the air in the atmosphere pressing against you? Not usually, but air actually exerts a lot of pressure because theres so much of it. The atmosphere rises high above Earths surface, so it contains a huge number of gas particles. Most of them are concentrated close to Earths surface because of gravity and the weight of all the air in the atmosphere above them. As a result, air pressure is greatest at sea level and drops rapidly as you go higher in altitude. The Figure 1.3 shows how air pressure falls from sea level to the top of the atmosphere. In the graph, air pressure is measured in a unit called the millibar (mb). The SI unit of pressure is newton per square centimeter (N/cm2 ). Q: The top of Mount Everest is almost 9 km above sea level. What is the pressure of the atmosphere at this altitude? A: Air pressure at the top of Mount Everest is about 260 mb. This is only about 25 percent of air pressure at sea level, which is 1013.2 mb. No wonder its hard for climbers to breathe when they get close to Mount Everests summit! | text | null |
L_0918 | history of science | T_4503 | People have probably wondered about the natural world for as long as there have been people. So its no surprise that science has roots that go back thousands of years. Some of the earliest contributions to science were made by Greek philosophers more than two thousand years ago. It wasnt until many centuries later, however, that the scientific method and experimentation were introduced. The dawn of modern science occurred even more recently. It is generally traced back to the scientific revolution, which took place in Europe starting in the 1500s. | text | null |
L_0918 | history of science | T_4504 | A Greek philosopher named Thales, who lived around 600 BCE, has been called the father of science for his ideas about the natural world. He proposed that natural events such as lightning and earthquakes have natural causes. Up until then, people understood such events to be the acts of gods or other supernatural forces. Q: Why was Thales idea about natural causes such an important contribution to science? A: Natural causes can be investigated and understood, whereas gods or other supernatural causes are above nature and not suitable for investigation. Just a few hundred years after Thales, the Greek philosopher Aristotle made a very important contribution to science. You can see what Aristotle looked like in the Figure 1.1. Prior to Aristotle, other philosophers believed that they could find the truth about the natural world by inward reflectionin other words, just by thinking about it. Aristotle, in contrast, thought that truth about the natural world could come only from observations of nature and inductive reasoning. He argued that knowledge of nature must be based on evidence and logic. This idea is called empiricism, and it is the basis of science today. Aristotle introduced the idea of empiricism around 350 BCE. It is a hallmark of modern science. | text | null |
L_0918 | history of science | T_4505 | In the first 1000 years CE, Europe went through a period called the Dark Ages. Science and learning in general were all but abandoned. However, in other parts of the world science flourished. During this period, some of the most important contributions to science were made by Persian scholars. For example, during the 700s CE, a Persian scientist named Geber introduced the scientific method and experimentation in chemistry. His ideas and methods were later adopted by European chemists. Today, Geber is known as the father of chemistry. | text | null |
L_0918 | history of science | T_4506 | Starting in the mid-1500s, a scientific revolution occurred in Europe. This was the beginning of modern Western science. Many scientific advances were made during a period of just a couple of hundred years. The revolution in science began when Copernicus made the first convincing arguments that the sunnot Earthis the center of what we now call the solar system. (You can see both models of the solar system in the Figure 1.2.) This was a drastic shift in thinking about Earths place in the cosmos. Around 1600, the Italian scientist Galileo greatly improved the telescope, which had just been invented, and made many important discoveries in the field of astronomy. Some of Galileos observations provided additional evidence for Copernicus sun-centered solar system. Q: Copernicus ideas about the solar system were so influential that the scientific revolution is sometimes called the Copernican revolution. Why do you think Copernicus ideas led to a revolution in science? A: Copernicus ideas about the solar system are considered to be the starting point of modern astronomy. They changed how all future scientists interpreted observations in astronomy. They also led to a flurry of new scientific investigation. Other contributions to science that occurred during the scientific revolution include: Keplers laws of planetary motion The model on the left shows what people believed about the solar system before Copernicus introduced the model on the right. Newtons law of universal gravitation Newtons three laws of motion | text | null |
L_0918 | history of science | T_4507 | Another major shift in science occurred with the work of Albert Einstein (the rock star scientist pictured in the opening image). In 1916, Einstein published his general theory of relativity. This theory relates matter and energy. It also explains gravity as a property of space and time (rather than a property of matter as Newton thought). Einsteins theory has been supported by all evidence and observations to date, whereas Newtons law of gravity does not apply to all cases. Einsteins theory is still the accepted explanation for gravity today. Q: How might Einsteins theory have influenced the course of science? A: Einsteins theory suggested new areas of investigation. Many predictions based on the theory were later found to be true. For example, black holes in the universe were predicted by Einsteins theory and later confirmed by scientific evidence. | text | null |
L_0922 | hypothesis | T_4520 | The word hypothesis can be defined as an "educated guess." For example, it might be an educated guess about why a natural event occurs. But not all hypotheseseven those about the natural worldare scientific hypotheses. What makes a statement a scientific hypothesis rather than just an educated guess? A scientific hypothesis must meet two criteria: A scientific hypothesis must be testable. A scientific hypothesis must be falsifiable. | text | null |
L_0922 | hypothesis | T_4521 | For a hypothesis to be testable means that it is possible to make observations that agree or disagree with it. If a hypothesis cannot be tested by making observations, it is not scientific. Consider this statement: "There are invisible creatures all around us that we can never observe in any way." This statement may or may not be true, but it is not a scientific hypothesis. Thats because it cant be tested. Given the nature of the hypothesis, there are no observations a scientist could make to test whether or not it is false. | text | null |
L_0922 | hypothesis | T_4522 | A hypothesis may be testable, but even that isnt enough for it to be a scientific hypothesis. In addition, it must be possible to show that the hypothesis is false if it really is false. Consider this statement: There are other planets in the universe where life exists. This statement is testable. If it is true, it is at least theoretically possible to find evidence showing that its true. For example, a spacecraft could be sent from Earth to explore the universe and report back if it discovers an inhabited planet. If such a planet were found, it would prove the statement is true. However, the statement isnt a scientific hypothesis. Why? If it is false, its not possible to show that its false. The spacecraft may never find an inhabited planet, but that doesnt necessarily mean there isnt one. Given the vastness of the universe, we would never be able to check every planet for life! | text | null |
L_0922 | hypothesis | T_4523 | Lets consider one last example, which is illustrated in the Figure 1.1: "Any two objects dropped at the same time from the same height will reach the ground at the same time (assuming the absence of air resistance)." Is this statement testable? Yes. You could drop two objects at the same time from the same height and observe when they reach the ground. Of course, you would have to drop the objects in the absence of air to prevent air resistance, but at least such a test is theoretically possible. Is the statement falsifiable if it really is false? Again, the answer is yes. You can easily test many combinations of two objects and if any two objects do not reach the ground at the same time, then the hypothesis is false. If a hypothesis really is false, it should be relatively easy to disprove it. | text | null |
L_0922 | hypothesis | T_4524 | If the hypothesis above about falling objects really were false, it is likely that this would be discovered sooner or later after enough objects had been dropped. It takes just one exception to disprove a hypothesis. But what if the hypothesis really is true? Can this be demonstrated as well? No; it would require testing all possible combinations of objects to show that they always reach the ground at the same time. This is impossible. New objects are being made all the time that would have to be tested. Its always possible an exception would be found in the future to disprove the hypothesis. Although you cant prove conclusively that a hypothesis is true, the more evidence you gather in support of it, the more likely it is to be true. | text | null |
L_0961 | nature of science | T_4644 | Science is more about gaining knowledge than it is about simply having knowledge. Science is a way of learning about the natural world that is based on evidence and logic. In other words, science is a process, not just a body of facts. Through the process of science, our knowledge of the world advances. | text | null |
L_0961 | nature of science | T_4645 | Scientists may focus on very different aspects of the natural world. For example, some scientists focus on the world of tiny objects, such as atoms and molecules. Other scientists devote their attention to huge objects, such as the sun and other stars. But all scientists have at least one thing in common. They want to understand how and why things happen. Achieving this understanding is the goal of science. Have you ever experienced the thrill of an exciting fireworks show like the one pictured in the Figure 1.1? Fireworks show how the goal of science leads to discovery. Fireworks were invented at least 2000 years ago in China, but explaining how and why they work didnt happen until much later. It wasnt until scientists had learned about elements and chemical reactions that they could explain what caused fireworks to create brilliant bursts of light and deep rumbling booms. Fireworks were invented long before sci- entists could actually explain how and why they explode. | text | null |
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