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L_0953 | microwaves | T_4620 | Radar stands for radio detection and ranging. In police radar, a radar gun sends out short bursts of microwaves. The microwaves reflect back from oncoming vehicles and are detected by a receiver in the radar gun. The frequency of the reflected waves is used to compute the speed of the vehicles. Radar is also used for tracking storms, detecting air traffic, and other purposes. Q: How are reflected microwaves used to determine the speed of oncoming cars (see Figure 1.3)? A: As the car approaches the radar gun, the reflected microwaves get bunched up in front of the car. Therefore, the waves the receiver detects have a higher frequency than they would if they were being reflected from a stationary object. The faster the car is moving, the greater the increase in the frequency of the waves. This is an example of the Doppler effect, which can also occur with sound waves. | text | null |
L_0954 | mirrors | T_4621 | A mirror is typically made of glass with a shiny metal backing that reflects all the light that strikes it. When a mirror reflects light, it forms an image. An image is a copy of an object that is formed by reflection or refraction. Mirrors may have flat or curved surfaces. The shape of a mirrors surface determines the type of image it forms. For example, some mirrors form real images, and other mirrors form virtual images. Whats the difference between real and virtual images? A real image forms in front of a mirror where reflected light rays actually meet. It is a true image that could be projected on a screen. A virtual image appears to be on the other side of the mirror. Of course, reflected rays dont actually go through the mirror to the other side, so a virtual image doesnt really exist. It just appears to exist to the human brain. Q: Look back at the image of the girl pointing at her image in the mirror. Which type of image is it, real or virtual? A: The image of the girl is a virtual image. It appears to be on the other side of the mirror from the girl. | text | null |
L_0954 | mirrors | T_4622 | The mirror in the opening photo is a plane mirror. This is the most common type of mirror. It has a flat reflective surface and forms only virtual images. The image formed by a plane mirror is also right-side up and life sized. But something is different about the image compared with the real object in front of the mirror. Left and right are reversed. Look at the girl brushing her teeth in the Figure 1.1. She is using her left hand to brush her teeth, but her image (on the left) appears to be brushing her teeth with the right hand. All plane mirrors reverse left and right in this way. The term mirror image refers to how left and right are reversed in an image compared with the object. | text | null |
L_0954 | mirrors | T_4623 | Some mirrors have a curved rather than flat surface. Curved mirrors can be concave or convex. A concave mirror is shaped like the inside of a bowl. This type of mirror forms either real or virtual images, depending on where the object is placed relative to the focal point. The focal point is the point in front of the mirror where the reflected rays meet. You can see how concave mirrors form images in the Figure 1.2. Concave mirrors are used behind car headlights. They focus the light and make it brighter. Concave mirrors are also used in some telescopes. | text | null |
L_0954 | mirrors | T_4624 | The other type of curved mirror, a convex mirror, is shaped like the outside of a bowl. Because of its shape, it can gather and reflect light from a wide area. As you can see in the Figure 1.3, a convex mirror forms only virtual images that are right-side up and smaller than the actual object. Q: Convex mirrors are used as side mirrors on cars. You can see one in the Figure 1.4. Why is a convex mirror good for this purpose? A: Because it gathers light over a wide area, a convex mirror gives the driver a wider view of the area around the vehicle than a plane mirror would. | text | null |
L_0954 | mirrors | T_4624 | The other type of curved mirror, a convex mirror, is shaped like the outside of a bowl. Because of its shape, it can gather and reflect light from a wide area. As you can see in the Figure 1.3, a convex mirror forms only virtual images that are right-side up and smaller than the actual object. Q: Convex mirrors are used as side mirrors on cars. You can see one in the Figure 1.4. Why is a convex mirror good for this purpose? A: Because it gathers light over a wide area, a convex mirror gives the driver a wider view of the area around the vehicle than a plane mirror would. | text | null |
L_0956 | modern periodic table | T_4629 | In the 1860s, a scientist named Dmitri Mendeleev also saw the need to organize the elements. He created a table in which he arranged all of the elements by increasing atomic mass from left to right across each row. When he placed eight elements in each row and then started again in the next row, each column of the table contained elements with similar properties. He called the columns of elements groups. Mendeleevs table is called a periodic table and the rows are called periods. Thats because the table keeps repeating from row to row, and periodic means repeating. | text | null |
L_0956 | modern periodic table | T_4630 | A periodic table is still used today to organize the elements. You can see a simple version of the modern periodic table in the Figure 1.1. The modern table is based on Mendeleevs table, except the modern table arranges the elements by increasing atomic number instead of atomic mass. Atomic number is the number of protons in an atom, and this number is unique for each element. The modern table has more elements than Mendeleevs table because many elements have been discovered since Mendeleevs time. | text | null |
L_0956 | modern periodic table | T_4631 | In the Figure 1.1, each element is represented by its chemical symbol, which consists of one or two letters. The first letter of the symbol is always written in upper case, and the second letterif there is oneis always written in lower case. For example, the symbol for copper is Cu. It stands for cuprum, which is the Latin word for copper. The number above each symbol in the table is its unique atomic number. Notice how the atomic numbers increase from left to right and from top to bottom in the table. Q: Find the symbol for copper in the Figure 1.1. What is its atomic number? What does this number represent? A: The atomic number of copper is 29. This number represents the number of protons in each atom of copper. (Copper is the element that makes up the coil of wire in photo A of the opening sequence of photos.) | text | null |
L_0956 | modern periodic table | T_4632 | Rows of the modern periodic table are called periods, as they are in Mendeleevs table. From left to right across a period, each element has one more proton than the element before it. Some periods in the modern periodic table are longer than others. For example, period 1 contains only two elements: hydrogen (H) and helium (He). In contrast, periods 6 and 7 are so long that many of their elements are placed below the main part of the table. They are the elements starting with lanthanum (La) in period 6 and actinium (Ac) in period 7. Some elements in period 7 have not yet been named. They are represented by temporary three-letter symbols, such as Uub. The number of each period represents the number of energy levels that have electrons in them for atoms of each element in that period. Q: Find calcium (Ca) in the Figure 1.1. How many energy levels have electrons in them for atoms of calcium? A: Calcium is in period 4, so its atoms have electrons in them for the first four energy levels. | text | null |
L_0956 | modern periodic table | T_4633 | Columns of the modern table are called groups, as they are in Mendeleevs table. However, the modern table has many more groups18 compared with just 8 in Mendeleevs table. Elements in the same group have similar properties. For example, all elements in group 18 are colorless, odorless gases, such as neon (Ne). (Neon is the element inside the light in opening photo C.) In contrast, all elements in group 1 are very reactive solids. They react explosively with water, as you can see in the video and Figure 1.2. Click image to the left or use the URL below. URL: The alkali metal sodium (Na) reacting with water. | text | null |
L_0956 | modern periodic table | T_4634 | All elements can be classified in one of three classes: metals, metalloids, or nonmetals. Elements in each class share certain basic properties. For example, elements in the metals class can conduct electricity, whereas elements in the nonmetals class generally cannot. Elements in the metalloids class fall in between the metals and nonmetals in their properties. An example of a metalloid is arsenic (As). (Arsenic is the element in opening photo B.) In the periodic table above, elements are color coded to show their class. As you move from left to right across each period of the table, the elements change from metals to metalloids to nonmetals. Q: To which class of elements does copper (Cu) belong: metal, metalloid, or nonmetal? Identify three other elements in this class. A: In the Figure 1.1, the cell for copper is colored blue. This means that copper belongs to the metals class. Other elements in the metals class include iron (Fe), sodium (Na), and gold (Au). It is apparent from the table that the majority of elements are metals. | text | null |
L_0957 | molecular compounds | T_4635 | Compounds that form from two or more nonmetallic elements, such as carbon and hydrogen, are called covalent compounds. In a covalent compound, atoms of the different elements are held together in molecules by covalent bonds. These are chemical bonds in which atoms share valence electrons. The force of attraction between the shared electrons and the positive nuclei of both atoms holds the atoms together in the molecule. A molecule is the smallest particle of a covalent compound that still has the properties of the compound. The largest, most complex covalent molecules have thousands of atoms. Examples include proteins and carbohy- drates, which are compounds in living things. The smallest, simplest covalent compounds have molecules with just two atoms. An example is hydrogen chloride (HCl). It consists of one hydrogen atom and one chlorine atom, as you can see in the Figure 1.1. | text | null |
L_0957 | molecular compounds | T_4636 | To name simple covalent compounds, follow these rules: Start with the name of the element closer to the left side of the periodic table. Follow this with the name of element closer to the right of the periodic table. Give this second name the suffix -ide. Use prefixes to represent the numbers of the different atoms in each molecule of the compound. The most commonly used prefixes are shown in the Table 1.1. Number 1 2 3 4 5 6 Prefix mono- (or none) di- tri- tetra- penta- hexa- Q: What is the name of the compound that contains three oxygen atoms and two nitrogen atoms? A: The compound is named dinitrogen trioxide. Nitrogen is named first because it is farther to the left in the periodic table than oxygen. Oxygen is given the -ide suffix because it is the second element named in the compound. The prefix di- is added to nitrogen to show that there are two atoms of nitrogen in each molecule of the compound. The prefix tri- is added to oxygen to show that there are three atoms of oxygen in each molecule. In the chemical formula for a covalent compound, the numbers of the different atoms in a molecule are represented by subscripts. For example, the formula for the compound named carbon dioxide is CO2 . Q: What is the chemical formula for dinitrogen trioxide? A: The chemical formula is N2 O3 . | text | null |
L_0957 | molecular compounds | T_4637 | The covalent bonds of covalent compounds are responsible for many of the properties of the compounds. Because valence electrons are shared in covalent compounds, rather than transferred between atoms as they are in ionic compounds, covalent compounds have very different properties than ionic compounds. Many covalent compounds, especially those containing carbon and hydrogen, burn easily. In contrast, many ionic compounds do not burn. Many covalent compounds do not dissolve in water, whereas most ionic compounds dissolve well in water. Unlike ionic compounds, covalent compounds do not have freely moving electrons, so they cannot conduct Name of Compound(Chemical For- mula) Sodium chloride (NaCl) Lithium fluoride (LiF) Type of Compound Boiling Point ( C) ionic ionic 1413 1676 Q: The two covalent compounds in the table are gases at room temperature, which is 20 C. For a compound to be a liquid at room temperature, what does its boiling point have to be? A: To be a liquid at room temperature, a covalent compound has to have a boiling point higher than 20 C. Water is an example of a covalent compound that is a liquid at room temperature. The boiling point of water is 100 C. | text | null |
L_0958 | momentum | T_4638 | Momentum is a property of a moving object that makes it hard to stop. The more mass it has or the faster its moving, the greater its momentum. Momentum equals mass times velocity and is represented by the equation: Momentum = Mass Velocity Q: What is Codys momentum as he stands at the top of the ramp? A: Cody has no momentum as he stands there because he isnt moving. In other words, his velocity is zero. However, Cody will gain momentum as he starts moving down the ramp and picks up speed. Q: Codys older brother Jerod is pictured in the Figure 1.1. If Jerod were to travel down the ramp at the same velocity as Cody, who would have greater momentum? Who would be harder to stop? A: Jerod obviously has greater mass than Cody, so he would have greater momentum. He would also be harder to stop. | text | null |
L_0958 | momentum | T_4639 | To calculate momentum with the equation above, mass is measured in (kg), and velocity is measured in meters per second (m/s). For example, Cody and his skateboard have a combined mass of 40 kg. If Cody is traveling at a velocity of 1.1 m/s by the time he reaches the bottom of the ramp, then his momentum is: Momentum = 40 kg 1.1 m/s = 44 kg m/s Note that the SI unit for momentum is kg m/s. Q: The combined mass of Jerod and his skateboard is 68 kg. If Jerod goes down the ramp at the same velocity as Cody, what is his momentum at the bottom of the ramp? A: His momentum is: Momentum = 68 kg 1.1 m/s = 75 kg m/s | text | null |
L_0959 | motion | T_4640 | In science, motion is defined as a change in position. An objects position is its location. Besides the wings of the hummingbird in the opening image, you can see other examples of motion in the Figure 1.1. In each case, the position of something is changing. Q: In each picture in the Figure 1.1, what is moving and how is its position changing? A: The train and all its passengers are speeding straight down a track to the next station. The man and his bike are racing along a curving highway. The geese are flying over their wetland environment. The meteor is shooting through the atmosphere toward Earth, burning up as it goes. | text | null |
L_0959 | motion | T_4641 | Theres more to motion than objects simply changing position. Youll see why when you consider the following example. Assume that the school bus pictured in the Figure 1.2 passes by you as you stand on the sidewalk. Its obvious to you that the bus is moving, but what about to the children inside the bus? The bus isnt moving relative to them, and if they look at the other children sitting on the bus, they wont appear to be moving either. If the ride is really smooth, the children may only be able to tell that the bus is moving by looking out the window and seeing you and the trees whizzing by. This example shows that how we perceive motion depends on our frame of reference. Frame of reference refers to something that is not moving with respect to an observer that can be used to detect motion. For the children on the bus, if they use other children riding the bus as their frame of reference, they do not appear to be moving. But if they use objects outside the bus as their frame of reference, they can tell they are moving. Q: What is your frame of reference if you are standing on the sidewalk and see the bus go by? How can you tell that the bus is moving? A: Your frame of reference might be the trees and other stationary objects across the street. As the bus goes by, it momentarily blocks your view of these objects, and this helps you detect the bus motion. | text | null |
L_0959 | motion | T_4641 | Theres more to motion than objects simply changing position. Youll see why when you consider the following example. Assume that the school bus pictured in the Figure 1.2 passes by you as you stand on the sidewalk. Its obvious to you that the bus is moving, but what about to the children inside the bus? The bus isnt moving relative to them, and if they look at the other children sitting on the bus, they wont appear to be moving either. If the ride is really smooth, the children may only be able to tell that the bus is moving by looking out the window and seeing you and the trees whizzing by. This example shows that how we perceive motion depends on our frame of reference. Frame of reference refers to something that is not moving with respect to an observer that can be used to detect motion. For the children on the bus, if they use other children riding the bus as their frame of reference, they do not appear to be moving. But if they use objects outside the bus as their frame of reference, they can tell they are moving. Q: What is your frame of reference if you are standing on the sidewalk and see the bus go by? How can you tell that the bus is moving? A: Your frame of reference might be the trees and other stationary objects across the street. As the bus goes by, it momentarily blocks your view of these objects, and this helps you detect the bus motion. | text | null |
L_0960 | musical instruments | T_4642 | People have been using sound to make music for thousands of years. They have invented many different kinds of musical instruments. Despite their diversity, however, musical instruments share certain similarities. All musical instruments create sound by causing matter to vibrate. The vibrations start sound waves moving through the air. Most musical instruments use resonance to amplify the sound waves and make the sounds louder. Resonance occurs when an object vibrates in response to sound waves of a certain frequency. In a musical instrument such as a drum, the whole instrument and the air inside it may vibrate when the head of the drum is struck. Most musical instruments have a way of changing the frequency of the sound waves they produce. This changes the pitch of the sounds, or how high or low the sounds seem to a listener. | text | null |
L_0960 | musical instruments | T_4643 | There are three basic categories of musical instruments: percussion, wind, and stringed instruments. You can read in the Figure 1.1 how instruments in each category make sound and change pitch. Q: Can you name other instruments in each of the three categories of musical instruments? A: Other percussion instruments include drums and cymbals. Other wind instruments include trumpets and flutes. Other stringed instruments include guitars and harps. | text | null |
L_0962 | nature of technology | T_4647 | Printers like the one that made the plastic bicycle are a new type of technology. Technology is the application of science to solve problems. Because technology finds solutions to practical problems, new technologies may have major impacts on society, science, and industry. For example, some people predict that 3-D printing will revolutionize manufacturing. Q: Making products with 3-D printers has several advantages over making them with machines in factories. What do you think some of the advantages might be? A: Making products with 3-D printers would allow anyone anywhere to make just about anything, provided they have the printer, powder, and computer program. Suppose, for example, that you live in a remote location and need a new part for your car. The solution? Just download the design on your computer and print the part on your 3-D printer. Manufacturing would no longer require specially designed machines in factories that produce pollution. Another advantage of using 3-D printers to make products is that no materials are wasted. This would lower manufacturing costs as well as save natural resources. | text | null |
L_0962 | nature of technology | T_4648 | New technologies such as 3-D printers often evolve slowly as new materials, designs, or processes are invented. Solar-powered cars are a good example. For several decades, researchers have been working on developing practical solar-powered cars. Why? Cars powered by sunlight have at least two important advantages over gas-powered cars. The energy they use is free and available almost everywhere, and they produce no pollution. The timeline in Table Milestone 1954: First modern solar cell 1955: First solar car 1983: First practical solar car 1987: First World Solar Challenge 2008: First Commercial solar car The first modern solar cell was invented in 1954 by a team of researchers at Bell Labs in the U.S. It could convert light energy to enough electricity to power devices. In 1955, William G. Cobb of General Motors demon- strated his 15-inch-long Sunmobile, the worlds first solar-powered automobile. Its tiny electric motor was powered by 12 solar cells on top of the car. In 1983, the first drivable solar car was created by Hans Tholstrup, a Danish inventor who was influenced by the earlier Sunmobile. Called the Quiet Achiever, Tholstrups car was driven 4000 km across Australia. However, its average speed was only 23 km/h, despite having more than 700 solar cells on its top panel. Inspired by his success with the Quiet Achiever, in 1987 Tholstrup launched the first World Solar Chal- lenge. This was the worlds first solar car race. The race is now held every other year. In that first race, the winner was General Motors Sunraycer, shown here. It had an average speed of 67 km/h. Its aerodynamic shape helped it achieve that speed. In 2008, the first commercial solar car was introduced. Called the Venturi Astrolab, it has a top speed of 120 km/h. To go this fast while using very little energy, it is built of ultra-light materials. Its oversized body protects the driver in case of collision and provides a lot of surface area for solar cells. Q: Why was the invention of the solar cell important to the evolution of solar car technology? A: The solar car could not exist without the solar cell. This invention provided a way to convert light energy to electricity that could be used to run a device such as a car. Q: The 1955 Sunmobile was just a model car. It was too small for people to drive. Why was it an important achievement in the evolution of solar car technology? A: The car wasnt practical, but it was a working solar car. It showed people that solar car technology is possible. It spurred others, including Hans Tholstrup, to work on solar cars that people could actually drive. Q: How have the World Solar Challenge races influenced the development of solar cars? A: The races have drawn a lot of attention to solar car development. The challenge of winning a race has also stimulated developers to keep improving the performance of solar cars so they can go faster and farther on solar power alone. | text | null |
L_0963 | neutrons | T_4649 | A neutron is one of three main particles that make up the atom. The other two particles are the proton and electron. Atoms of all elementsexcept for most atoms of hydrogenhave neutrons in their nucleus. The nucleus is the small, dense region at the center of an atom where protons are also found. Atoms generally have about the same number of neutrons as protons. For example, all carbon atoms have six protons and most also have six neutrons. A model of a carbon atom is shown in the Figure 1.1. Click image to the left or use the URL below. URL: | text | null |
L_0963 | neutrons | T_4650 | Unlike protons and electrons, which are electrically charged, neutrons have no charge. In other words, they are electrically neutral. Thats why the neutrons in the diagram above are labeled n0 . The zero stands for zero charge. The mass of a neutron is slightly greater than the mass of a proton, which is 1 atomic mass unit (amu). (An atomic mass unit equals about 1.67 1027 kilograms.) A neutron also has about the same diameter as a proton, or 1.7 1017 meters. | text | null |
L_0963 | neutrons | T_4651 | All the atoms of a given element have the same number of protons and electrons. The number of neutrons, however, may vary for atoms of the same element. For example, almost 99 percent of carbon atoms have six neutrons, but the rest have either seven or eight neutrons. Atoms of an element that differ in their numbers of neutrons are called isotopes. The nuclei of these isotopes of carbon are shown in the Figure 1.2. The isotope called carbon-14 is used to find the ages of fossils. Q: Notice the names of the carbon isotopes in the diagram. Based on this example, infer how isotopes of an element are named. A: Isotopes of an element are named for their total number of protons and neutrons. Q: The element oxygen has 8 protons. How many protons and neutrons are there in oxygen-17? A: Oxygen-17like all atoms of oxygenhas 8 protons. Its name provides the clue that it has a total of 17 protons and neutrons. Therefore, it must have 9 neutrons (8 + 9 = 17). | text | null |
L_0963 | neutrons | T_4652 | Neutrons consist of fundamental particles known as quarks and gluons. Each neutron contains three quarks, as shown in the diagram below. Two of the quarks are called down quarks (d) and the third quark is called an up quark (u). Gluons (represented by wavy black lines in the diagram) are fundamental particles that are given off or absorbed by quarks. They carry the strong nuclear force that holds together quarks in a neutron. | text | null |
L_0964 | newtons first law | T_4653 | Did you ever ride a skateboard? Even if you didnt, you probably know that to start a skateboard rolling over a level surface, you need to push off with one foot against the ground. Thats what Coreys friend Nina is doing in this picture 1.1. Do you know how to stop a skateboard once it starts rolling? Look how Ninas friend Laura does it in the Figure the skateboard. Even if Laura didnt try to stop the skateboard, it would stop sooner or later. Thats because theres also friction between the wheels and the pavement. Friction is a force that counters all kinds of motion. It occurs whenever two surfaces come into contact. | text | null |
L_0964 | newtons first law | T_4653 | Did you ever ride a skateboard? Even if you didnt, you probably know that to start a skateboard rolling over a level surface, you need to push off with one foot against the ground. Thats what Coreys friend Nina is doing in this picture 1.1. Do you know how to stop a skateboard once it starts rolling? Look how Ninas friend Laura does it in the Figure the skateboard. Even if Laura didnt try to stop the skateboard, it would stop sooner or later. Thats because theres also friction between the wheels and the pavement. Friction is a force that counters all kinds of motion. It occurs whenever two surfaces come into contact. | text | null |
L_0964 | newtons first law | T_4654 | If you understand how a skateboard starts and stops, then you already know something about Newtons first law of motion. This law was developed by English scientist Isaac Newton around 1700. Newton was one of the greatest scientists of all time. He developed three laws of motion and the law of gravity, among many other contributions. Newtons first law of motion states that an object at rest will remain at rest and an object in motion will stay in motion unless it is acted on by an unbalanced force. Without an unbalanced force, a moving object will not only keep moving, but its speed and direction will also remain the same. Newtons first law of motion is often called the law of inertia because inertia is the tendency of an object to resist a change in its motion. If an object is already at rest, inertia will keep it at rest. If an object is already in motion, inertia will keep it moving. | text | null |
L_0964 | newtons first law | T_4655 | Coreys friend Jerod likes to skate on the flat banks at Newtons Skate Park. Thats Jerod in the Figure 1.3. As he reaches the top of a bank, he turns his skateboard to go back down. To change direction, he presses down with his heels on one edge of the skateboard. This causes the skateboard to turn in the opposite direction. | text | null |
L_0964 | newtons first law | T_4656 | Q: How does Nina use Newtons first law to start her skateboard rolling? A: The skateboard wont move unless Nina pushes off from the pavement with one foot. The force she applies when she pushes off is stronger than the force of friction that opposes the skateboards motion. As a result, the force on the skateboard is unbalanced, and the skateboard moves forward. Q: How does Nina use Newtons first law to stop her skateboard? A: Once the skateboard starts moving, it would keep moving at the same speed and in the same direction if not for another unbalanced force. That force is friction between the skateboard and the pavement. The force of friction is unbalanced because Nina is no longer pushing with her foot to keep the skateboard moving. Thats why the skateboard stops. Q: How does Jerod use Newtons first law of motion to change the direction of his skateboard? A: Pressing down on just one side of a skateboard creates an unbalanced force. The unbalanced force causes the skateboard to turn toward the other side. In the picture, Jerod is pressing down with his heels, so the skateboard turns toward his toes. | text | null |
L_0965 | newtons law of gravity | T_4657 | Newton was the first one to suggest that gravity is universal and affects all objects in the universe. Thats why Newtons law of gravity is called the law of universal gravitation. Universal gravitation means that the force that causes an apple to fall from a tree to the ground is the same force that causes the moon to keep moving around Earth. Universal gravitation also means that while Earth exerts a pull on you, you exert a pull on Earth. In fact, there is gravity between you and every mass around youyour desk, your book, your pen. Even tiny molecules of gas are attracted to one another by the force of gravity. Q: Newtons law of universal gravitation had a huge impact on how people thought about the universe. Why do you think it was so important? A: Newtons law was the first scientific law that applied to the entire universe. It explains the motion of objects not only on Earth but in outer space as well. | text | null |
L_0965 | newtons law of gravity | T_4658 | Newtons law also states that the strength of gravity between any two objects depends on two factors: the masses of the objects and the distance between them. Objects with greater mass have a stronger force of gravity between them. For example, because Earth is so massive, it attracts you and your desk more strongly that you and your desk attract each other. Thats why you and the desk remain in place on the floor rather than moving toward one another. Objects that are closer together have a stronger force of gravity between them. For example, the moon is closer to Earth than it is to the more massive sun, so the force of gravity is greater between the moon and Earth than between the moon and the sun. Thats why the moon circles around Earth rather than the sun. You can see this in the Figure 1.1. | text | null |
L_0966 | newtons second law | T_4659 | Whenever an object speeds up, slows down, or changes direction, it accelerates. Acceleration occurs whenever an unbalanced force acts on an object. Two factors affect the acceleration of an object: the net force acting on the object and the objects mass. Newtons second law of motion describes how force and mass affect acceleration. The law states that the acceleration of an object equals the net force acting on the object divided by the objects mass. This can be represented by the equation: Acceleration = or a = Net force Mass F m Q: While Tony races along on his rollerblades, what net force is acting on the skates? A: Tony exerts a backward force against the ground, as you can see in the Figure 1.1, first with one skate and then with the other. This force pushes him forward. Although friction partly counters the forward motion of the skates, it is weaker than the force Tony exerts. Therefore, there is a net forward force on the skates. | text | null |
L_0966 | newtons second law | T_4660 | Newtons second law shows that there is a direct relationship between force and acceleration. The greater the force that is applied to an object of a given mass, the more the object will accelerate. For example, doubling the force on the object doubles its acceleration. The relationship between mass and acceleration is different. It is an inverse relationship. In an inverse relationship, when one variable increases, the other variable decreases. The greater the mass of an object, the less it will accelerate when a given force is applied. For example, doubling the mass of an object results in only half as much acceleration for the same amount of force. Q: Tony has greater mass than the other two boys he is racing (pictured in the opening image). How will this affect his acceleration around the track? A: Tonys greater mass will result in less acceleration for the same amount of force. | text | null |
L_0967 | newtons third law | T_4661 | Newtons third law of motion explains how Jerod starts his skateboard moving. This law states that every action has an equal and opposite reaction. This means that forces always act in pairs. First an action occursJerod pushes against the ground with his foot. Then a reaction occursJerod moves forward on his skateboard. The reaction is always equal in strength to the action but in the opposite direction. Q: If Jerod pushes against the ground with greater force, how will this affect his forward motion? A: His action force will be greater, so the reaction force will be greater as well. Jerod will be pushed forward with more force, and this will make him go faster and farther. | text | null |
L_0967 | newtons third law | T_4662 | The forces involved in actions and reactions can be represented with arrows. The way an arrow points shows the direction of the force, and the size of the arrow represents the strength of the force. Look at the skateboarders in the Figure 1.1. In the top row, the arrows represent the forces with which the skateboarders push against each other. This is the action. In the bottom row, the arrows represent the forces with which the skateboarders move apart. This is the reaction. Compare the top and bottom arrows. They point in different directions, but they are the same size. This shows that the reaction forces are equal and opposite to the action forces. | text | null |
L_0967 | newtons third law | T_4663 | Because action and reaction forces are equal and opposite, you might think they would cancel out, as balanced forces do. But you would be wrong. Balanced forces are equal and opposite forces that act on the same object. Thats why they cancel out. Action-reaction forces are equal and opposite forces that act on different objects, so they dont cancel out. In fact, they often result in motion. Think about Jerod again. He applies force with his foot to the ground, whereas the ground applies force to Jerod and the skateboard, causing them to move forward. Q: Actions and reactions occur all the time. Can you think of an example in your daily life? A: Heres one example. If you lean on something like a wall or your locker, you are applying force to it. The wall or locker applies an equal and opposite force to you. If it didnt, you would go right through it or else it would tip over. | text | null |
L_0968 | noble gases | T_4664 | Noble gases are nonreactive, nonmetallic elements in group 18 of the periodic table. As you can see in the periodic table below, noble gases include helium (He), neon (Ne), argon (Ar), krypton (Kr), xenon (Xe), and radon (Rn). All noble gases are colorless and odorless. They also have low boiling points, explaining why they are gases at room temperature. Radon, at the bottom of the group, is radioactive, so it constantly decays to other elements. Click image to the left or use the URL below. URL: Q: Based on their position in the periodic table (Figure 1.1), how many valence electrons do you think noble gases have? A: The number of valence electrons starts at one for elements in group 1. It then increases by one from left to right across each period (row) of the periodic table for groups 1-2 and 13-18 (numbered 3-0 in the table above). Therefore, noble gases have eight valence electrons. | text | null |
L_0968 | noble gases | T_4665 | Noble gases are the least reactive of all known elements. Thats because with eight valence electrons, their outer energy levels are full. The only exception is helium, which has just two electrons. But helium also has a full outer energy level, because its only energy level (energy level 1) can hold a maximum of two electrons. A full outer energy level is the most stable arrangement of electrons. As a result, noble gases cannot become more stable by reacting with other elements and gaining or losing valence electrons. Therefore, noble gases are rarely involved in chemical reactions and almost never form compounds with other elements. | text | null |
L_0968 | noble gases | T_4666 | Because the noble gases are the least reactive of all elements, their eight valence electrons are used as the standard for nonreactivity and to explain how other elements interact. This is stated as the octet (group of eight) rule. According to this rule, atoms react to form compounds that allow them to have a group of eight valence electrons like the noble gases. For example, sodium (with one valence electron) reacts with chlorine (with seven valence electrons) to form the stable compound sodium chloride (table salt). In this reaction, sodium donates an electron and chlorine accepts it, giving each element an octet of valence electrons. | text | null |
L_0968 | noble gases | T_4667 | Did you ever get a birthday balloon like the one pictured 1.2? The balloon is filled with the noble gas helium. The gas is pumped from a tank into a Mylar balloon. Unlike a balloon filled with air, a balloon filled with helium needs to be weighted down so it wont float away. Q: Why does a helium balloon float away if its not weighted down? A: Helium atoms have just two protons, two neutrons, and two electrons, so they have less mass than any other atoms except hydrogen. As a result, helium is lighter than air, explaining why a helium balloon floats up into the air unless weighted down. Early incandescent light bulbs, like the one pictured in the Figure 1.3, didnt last very long. The filaments quickly burned out. Although air was pumped out of the bulb, it wasnt a complete vacuum. Oxygen in the small amount of air remaining inside the light bulb reacted with the metal filament. This corroded the filament and caused dark deposits on the glass. Filling a light bulb with argon gas prevents these problems. Thats why modern light bulbs are filled with argon. A: As a noble gas with eight electrons, argon doesnt react with the metal in the filament. This protects the filament and keeps the glass blub free of deposits. Noble gases are also used to fill the glass tubes of lighted signs like the one in the Figure 1.4. Although noble gases are chemically nonreactive, their electrons can be energized by sending an electric current through them. When this happens, the electrons jump to a higher energy level. When the electrons return to their original energy level, they give off energy as light. Different noble gases give off light of different colors. Neon gives off reddish-orange light, like the word Open in the sign below. Krypton gives off violet light and xenon gives off blue light. | text | null |
L_0968 | noble gases | T_4667 | Did you ever get a birthday balloon like the one pictured 1.2? The balloon is filled with the noble gas helium. The gas is pumped from a tank into a Mylar balloon. Unlike a balloon filled with air, a balloon filled with helium needs to be weighted down so it wont float away. Q: Why does a helium balloon float away if its not weighted down? A: Helium atoms have just two protons, two neutrons, and two electrons, so they have less mass than any other atoms except hydrogen. As a result, helium is lighter than air, explaining why a helium balloon floats up into the air unless weighted down. Early incandescent light bulbs, like the one pictured in the Figure 1.3, didnt last very long. The filaments quickly burned out. Although air was pumped out of the bulb, it wasnt a complete vacuum. Oxygen in the small amount of air remaining inside the light bulb reacted with the metal filament. This corroded the filament and caused dark deposits on the glass. Filling a light bulb with argon gas prevents these problems. Thats why modern light bulbs are filled with argon. A: As a noble gas with eight electrons, argon doesnt react with the metal in the filament. This protects the filament and keeps the glass blub free of deposits. Noble gases are also used to fill the glass tubes of lighted signs like the one in the Figure 1.4. Although noble gases are chemically nonreactive, their electrons can be energized by sending an electric current through them. When this happens, the electrons jump to a higher energy level. When the electrons return to their original energy level, they give off energy as light. Different noble gases give off light of different colors. Neon gives off reddish-orange light, like the word Open in the sign below. Krypton gives off violet light and xenon gives off blue light. | text | null |
L_0969 | nonmetals | T_4668 | Nonmetals are elements that generally do not conduct electricity. They are one of three classes of elements (the other two classes are metals and metalloids.) Nonmetals are the second largest of the three classes after metals. They are the elements located on the right side of the periodic table. Q: From left to right across each period (row) of the periodic table, each element has atoms with one more proton and one more electron than the element before it. How might this be related to the properties of nonmetals? A: Because nonmetals are on the right side of the periodic table, they have more electrons in their outer energy level than elements on the left side or in the middle of the periodic table. The number of electrons in the outer energy level of an atom determines many of its properties. | text | null |
L_0969 | nonmetals | T_4669 | As their name suggests, nonmetals generally have properties that are very different from the properties of metals. Properties of nonmetals include a relatively low boiling point, which explains why many of them are gases at room temperature. However, some nonmetals are solids at room temperature, including the three pictured above, and one nonmetalbromineis a liquid at room temperature. Other properties of nonmetals are illustrated and described in the Figure 1.1. | text | null |
L_0969 | nonmetals | T_4670 | Reactivity is how likely an element is to react chemically with other elements. Some nonmetals are extremely reactive, whereas others are completely nonreactive. What explains this variation in nonmetals? The answer is their number of valence electrons. These are the electrons in the outer energy level of an atom that are involved in interactions with other atoms. Lets look at two examples of nonmetals, fluorine and neon. Simple atomic models of these two elements are shown in the Figure 1.2. Q: Which element, fluorine or neon, do you predict is more reactive? A: Fluorine is more reactive than neon. Thats because it has seven of eight possible electrons in its outer energy level, whereas neon already has eight electrons in this energy level. Although neon has just one more electron than fluorine in its outer energy level, that one electron makes a huge difference. Fluorine needs one more electron to fill its outer energy level in order to have the most stable arrangement of electrons. Therefore, fluorine readily accepts an electron from any element that is equally eager to give one up, Click image to the left or use the URL below. URL: | text | null |
L_0969 | nonmetals | T_4670 | Reactivity is how likely an element is to react chemically with other elements. Some nonmetals are extremely reactive, whereas others are completely nonreactive. What explains this variation in nonmetals? The answer is their number of valence electrons. These are the electrons in the outer energy level of an atom that are involved in interactions with other atoms. Lets look at two examples of nonmetals, fluorine and neon. Simple atomic models of these two elements are shown in the Figure 1.2. Q: Which element, fluorine or neon, do you predict is more reactive? A: Fluorine is more reactive than neon. Thats because it has seven of eight possible electrons in its outer energy level, whereas neon already has eight electrons in this energy level. Although neon has just one more electron than fluorine in its outer energy level, that one electron makes a huge difference. Fluorine needs one more electron to fill its outer energy level in order to have the most stable arrangement of electrons. Therefore, fluorine readily accepts an electron from any element that is equally eager to give one up, Click image to the left or use the URL below. URL: | text | null |
L_0969 | nonmetals | T_4671 | Like most other nonmetals, fluorine cannot conduct electricity, and its electrons explain this as well. An electric current is a flow of electrons. Elements that readily give up electrons (the metals) can carry electric current because their electrons can flow freely. Elements that gain electrons instead of giving them up cannot carry electric current. They hold onto their electrons so they cannot flow. | text | null |
L_0970 | nuclear fission | T_4672 | Nuclear fission is the splitting of the nucleus of a radioactive atom into two smaller nuclei. This type of reaction releases a great deal of energy from a very small amount of matter. Fission of a tiny pellet of radioactive uranium- 235, like the one pictured in the Figure 1.1, releases as much energy as burning 1,000 kilograms of coal! Q: What causes the nucleus of uranium-235 atom to fission? A: Another particle collides with it. | text | null |
L_0970 | nuclear fission | T_4673 | The Figure 1.2 shows how nuclear fission of uranium-235 occurs. It begins when a uranium nucleus gains a neutron. This can happen naturally when a free neutron strikes it, or it can occur deliberately when a neutron is crashed into it in a nuclear power plant. In either case, the nucleus of uranium-235 becomes extremely unstable with the extra neutron. As a result, it splits into two smaller nuclei, krypton-92 and barium-141. The reaction also releases three neutrons and a great deal of energy. It can be represented by this nuclear equation: 235 U 92 141 + 1 neutron 92 36 Kr + 56 Ba + 3 neutrons + energy Note that the subscripts of the element symbols represent numbers of protons and the superscripts represent numbers of protons plus neutrons. | text | null |
L_0970 | nuclear fission | T_4674 | The neutrons released when uranium-235 fissions may crash into other uranium nuclei and cause them to fission as well. This can start a nuclear chain reaction. You can see how this happens in the Figure 1.3. In a chain reaction, one fission reaction leads to others, which lead to others, and so on. A nuclear chain reaction is similar to a pile of wood burning. If you start one piece of wood burning, enough heat is produced by the burning wood to start the rest of the pile burning without any further help from you. Click image to the left or use the URL below. URL: | text | null |
L_0970 | nuclear fission | T_4675 | If a nuclear chain reaction is uncontrolled, it produces a lot of energy all at once. This is what happens in an atomic bomb. However, if a nuclear chain reaction is controlled, it produces energy much more slowly. This is what occurs in a nuclear power plant. The reaction is controlled by inserting rods of nonfissioning material into the fissioning material. You can see this in the Figure 1.4. The radiation from the controlled fission is used to heat water and turn it to steam. The steam is under pressure and causes a turbine to spin. The spinning turbine runs a generator, which produces electricity. | text | null |
L_0970 | nuclear fission | T_4675 | If a nuclear chain reaction is uncontrolled, it produces a lot of energy all at once. This is what happens in an atomic bomb. However, if a nuclear chain reaction is controlled, it produces energy much more slowly. This is what occurs in a nuclear power plant. The reaction is controlled by inserting rods of nonfissioning material into the fissioning material. You can see this in the Figure 1.4. The radiation from the controlled fission is used to heat water and turn it to steam. The steam is under pressure and causes a turbine to spin. The spinning turbine runs a generator, which produces electricity. | text | null |
L_0970 | nuclear fission | T_4676 | In the U.S., the majority of electricity is produced by burning coal or other fossil fuels. This causes air pollution that harms the health of living things. The air pollution also causes acid rain and contributes to global warming. In addition, fossil fuels are nonrenewable resources, so if we keep using them, they will eventually run out. The main advantage of nuclear energy is that it doesnt release air pollution or cause the other environmental problems associated with the burning of fossil fuels. On the other other hand, radioactive elements are nonrenewable like fossil fuels and could eventually be used up. The main concern over the use of nuclear energy is the risk of radiation. Accidents at nuclear power plants can release harmful radiation that endangers people and other living things. Even without accidents, the used fuel that is left after nuclear fission reactions is still radioactive and very dangerous. It takes thousands of years for it to decay until it no longer releases harmful radiation. Therefore, used fuel must be stored securely to protect people and other living things. Click image to the left or use the URL below. URL: | text | null |
L_0971 | nuclear fusion | T_4677 | In nuclear fusion, two or more small nuclei combine to form a single, larger nucleus. You can see an example in the Figure 1.1. In this example, nuclei of two hydrogen isotopes (tritium and deuterium) fuse to form a helium nucleus. A neutron and a tremendous amount of energy are also released. | text | null |
L_0971 | nuclear fusion | T_4678 | Nuclear fusion of hydrogen to form helium occurs naturally in the sun and other stars. It takes place only at extremely high temperatures. Thats because a great deal of energy is needed to overcome the force of repulsion between the positively charged nuclei. The suns energy comes from fusion in its core, shown in the Figure 1.2. In the core, temperatures reach millions of degrees Kelvin. Click image to the left or use the URL below. URL: The Sun Q: Why doesnt nuclear fusion occur naturally on Earth? A: Nuclear fusion doesnt occur naturally on Earth because it requires temperatures far higher than Earth tempera- tures. | text | null |
L_0971 | nuclear fusion | T_4679 | Scientists are searching for ways to create controlled nuclear fusion reactions on Earth. Their goal is develop nuclear fusion power plants, where the energy from fusion of hydrogen nuclei can be converted to electricity. You can see how this might work in the Figure 1.3. In the thermonuclear reactor, radiation from fusion is used to heat water and produce steam. The steam can then be used to turn a turbine and generate electricity. The use of nuclear fusion for energy has several pros. Unlike nuclear fission, which involves dangerous radioactive elements, nuclear fusion involves just hydrogen and helium. These elements are harmless. Hydrogen is also very plentiful. There is a huge amount of hydrogen in ocean water. The hydrogen in just a gallon of water could produce as much energy by nuclear fusion as burning 1,140 liters (300 gallons) of gasoline! The hydrogen in the oceans would generate enough energy to supply all the worlds people for a very long time. Unfortunately, using energy from nuclear fusion is far from a reality. Scientists are a long way from developing the necessary technology. One problem is raising temperatures high enough for fusion to take place. Another problem is that matter this hot exists only in the plasma state. There are no known materials that can contain plasma, although a magnet might be able to do it. Thats because plasma consists of ions and responds to magnetism. Click image to the left or use the URL below. URL: | text | null |
L_0972 | nucleic acid classification | T_4680 | Nucleic acids are one of four classes of biochemical compounds. (The other three classes are carbohydrates, proteins, and lipids.) Nucleic acids include RNA (ribonucleic acid) as well as DNA (deoxyribonucleic acid). Both types of nucleic acids contain the elements carbon, hydrogen, oxygen, nitrogen, and phosphorus. Q: Which of the elements in DNA is not identified with any other class of biochemical compounds? A: All biochemical compounds contain carbon, hydrogen, and oxygen; and proteins as well as nucleic acids contain nitrogen. Phosphorus is the only element that is identified with nucleic acids. | text | null |
L_0972 | nucleic acid classification | T_4681 | Nucleic acids consist of chains of small molecules called nucleotides, which are held together by covalent bonds. The structure of a nucleotide is shown in the Figure 1.1. Each nucleotide consists of: 1. a phosphate group, which contains phosphorus and oxygen (PO4 ). 2. a sugar, which is deoxyribose (C5 H8 O4 ) in DNA and ribose (C5 H10 O5 ) in RNA. 3. one of four nitrogen-containing bases. (A base is a compound that is not neither acidic nor neutral.) In DNA, the bases are adenine, thymine, guanine, and cytosine. RNA has the base uracil instead of thymine, but the other three bases are the same. | text | null |
L_0972 | nucleic acid classification | T_4682 | RNA consists of just one chain of nucleotides. DNA consists of two chains. Nitrogen bases on the two chains of DNA form hydrogen bonds with each other. Hydrogen bonds are relatively weak bonds that form between a positively charged hydrogen atom in one molecule and a negatively charged atom in another molecule. Hydrogen bonds form only between adenine and thymine, and between guanine and cytosine. These bonds hold the two chains together and give DNA is characteristic double helix, or spiral, shape. You can see the shape of the DNA molecule in the Figure 1.2. Sugars and phosphate groups form the backbone of each chain of DNA. The bonded bases are called base pairs. Determining the structure of DNA was a huge scientific breakthrough. Q: Compare the structure of DNA to a spiral staircase. What part of the molecule do the stair steps represent? A: The steps represent the base pairs. | text | null |
L_0972 | nucleic acid classification | T_4683 | DNA stores genetic information in the cells of all living things. It contains the genetic code. This is the code that instructs cells how to make proteins. The instructions are encoded in the sequence of nitrogen bases in the nucleotide chains of DNA. RNA copies and interprets the genetic code in DNA and is also involved in the synthesis of proteins based on the code. Click image to the left or use the URL below. URL: Q: DNA is found only in the nucleus of cells, but proteins are synthesized in the cytoplasm of cells, outside of the nucleus. How do you think the instructions encoded in DNA reach the cytoplasm so they can be used to make proteins? A: After RNA copies the instructions in DNA, it carries them from the nucleus to a site of protein synthesis in the cytoplasm, where the instructions are translated into a protein. | text | null |
L_0976 | optical instruments | T_4691 | Optics is the study of visible light and the ways it can be used to extend human vision and do other tasks. Knowledge of light was needed for the invention of optical instruments such as microscopes, telescopes, and cameras, in addition to optical fibers. These instruments use mirrors and lenses to reflect and refract light and form images. Q: What is an image? A: An image is a copy of an object created by the reflection or refraction of visible light. | text | null |
L_0976 | optical instruments | T_4692 | A light microscope is an instrument that uses lenses to make enlarged images of objects that are too small for the unaided eye to see. A common type of light microscope is a compound microscope, like the one shown in the Figure lenses. The objective lenses are close to the object being viewed. They form an enlarged image of the object inside the microscope. The eyepiece lenses are close to the viewers eyes. They form an enlarged image of the first image. The magnifications of all the lenses are multiplied together to yield the overall magnification of the microscope. Some light microscopes can magnify objects more than 1000 times! Q: How has the microscope advanced scientific knowledge? A: The microscope has revealed secrets of the natural world like no other single invention. The microscope let scientists see entire new worlds, leading to many discoveriesespecially in biology and medicinethat could not have been made without it. Some examples include the discovery of cells and the identification of bacteria and other single-celled organisms. With the development of more powerful microscopes, viruses were discovered and even atoms finally became visible. These discoveries changed our ideas about the human body and the nature of life itself. | text | null |
L_0976 | optical instruments | T_4693 | Like microscopes, telescopes use convex lenses to make enlarged images. However, telescopes make enlarged images of objectssuch as distant starsthat only appear tiny because they are very far away. There are two basic types of telescopes: reflecting telescopes and refracting telescopes. The two types are compared in the Figure 1.2. They differ in how they collect light, but both use convex lenses to form enlarged images. Click image to the left or use the URL below. URL: | text | null |
L_0976 | optical instruments | T_4694 | A camera is an optical instrument that forms and records an image of an object. The image may be recorded on film or it may be detected by an electronic sensor that stores the image digitally. Regardless of how the image is recorded, all cameras form images in the same basic way, as shown in the Figure 1.3. Light passes through the lens at the front of the camera and enters the camera through an opening called the aperture. As light passes through the lens, it forms a reduced real image. The image focuses on film (or a sensor) at the back of the camera. The lens may be moved back and forth to bring the image into focus. The shutter controls the amount of light that actually strikes the film (or sensor). It stays open longer in dim light to let more light in. | text | null |
L_0976 | optical instruments | T_4695 | Did you ever see a cat chase after a laser light, like the one in Figure 1.4? A laser is a device that produces a very focused beam of visible light of just one wavelength and color. Waves of laser light are synchronized so the crests and troughs of the waves line up. The diagram in Figure 1.4 shows why a beam of laser light is so focused compared with ordinary light from a flashlight. The following Figure 1.5 provides a closer look at the tube where laser light is created. Electrons in a material such as a ruby crystal are stimulated to radiate photons of light of one wavelength. At each end of the tube is a concave mirror. The photons of light reflect back and forth in the tube off these mirrors. This focuses the light. The mirror at one end of the tube is partly transparent. A constant stream of photons passes through the transparent part, forming the laser beam. Click image to the left or use the URL below. URL: | text | null |
L_0976 | optical instruments | T_4695 | Did you ever see a cat chase after a laser light, like the one in Figure 1.4? A laser is a device that produces a very focused beam of visible light of just one wavelength and color. Waves of laser light are synchronized so the crests and troughs of the waves line up. The diagram in Figure 1.4 shows why a beam of laser light is so focused compared with ordinary light from a flashlight. The following Figure 1.5 provides a closer look at the tube where laser light is created. Electrons in a material such as a ruby crystal are stimulated to radiate photons of light of one wavelength. At each end of the tube is a concave mirror. The photons of light reflect back and forth in the tube off these mirrors. This focuses the light. The mirror at one end of the tube is partly transparent. A constant stream of photons passes through the transparent part, forming the laser beam. Click image to the left or use the URL below. URL: | text | null |
L_0976 | optical instruments | T_4696 | Besides entertaining a cat, laser light has many other uses. One use is carrying communication signals in optical fibers. Sounds or pictures are encoded in pulses of laser light, which are then sent through an optical fiber. All of the light reflects off the inside of the fiber, so none of it escapes. As a result, the signal remains strong even over long distances. More than one signal can travel through an optical fiber at the same time, as you can see in the Figure Q: When lasers were invented in 1960, they were called "a solution looking for a problem. Since then, they have been put to thousands of different uses. Can you name other ways that lasers are used? A: The first widespread use of lasers was the supermarket barcode scanner, introduced in 1974. The compact disc (CD) player was the first laser-equipped device commonly used by consumers, starting in 1982. The CD player was quickly followed by the laser printer. Some other uses of lasers include bloodless surgery, cutting and welding of metals, guiding missiles, thermometers, laser light shows, and acne treatments. The optical fiber in the diagram is much larger than a real optical fiber, which is only about as wide as a human hair. | text | null |
L_0977 | orbital motion | T_4697 | Earth and many other bodiesincluding asteroids, comets, and the other planetsmove around the sun in curved paths called orbits. Generally, the orbits are elliptical, or oval, in shape. You can see the shape of Earths orbit in the Figure 1.1. Because of the suns relatively strong gravity, Earth and the other bodies constantly fall toward the sun, but they stay far enough away from the sun because of their forward velocity to fall around the sun instead of into it. As a result, they keep orbiting the sun and never crash to its surface. The motion of Earth and the other bodies around the sun is called orbital motion. Orbital motion occurs whenever an object is moving forward and at the same time is pulled by gravity toward another object. | text | null |
L_0977 | orbital motion | T_4698 | Just as Earth orbits the sun, the moon also orbits Earth. The moon is affected by Earths gravity more than it is by the gravity of the sun because the moon is much closer to Earth. The gravity between Earth and the moon pulls the moon toward Earth. At the same time, the moon has forward velocity that partly counters the force of Earths gravity. So the moon orbits Earth instead of falling down to the surface of the planet. The Figure 1.2 shows the forces involved in the moons orbital motion around Earth. In the diagram, v represents the forward velocity of the moon, and a represents the acceleration due to gravity between Earth and the moon. The line encircling Earth shows the moons actual orbit, which results from the combination of v and a. | text | null |
L_0977 | orbital motion | T_4698 | Just as Earth orbits the sun, the moon also orbits Earth. The moon is affected by Earths gravity more than it is by the gravity of the sun because the moon is much closer to Earth. The gravity between Earth and the moon pulls the moon toward Earth. At the same time, the moon has forward velocity that partly counters the force of Earths gravity. So the moon orbits Earth instead of falling down to the surface of the planet. The Figure 1.2 shows the forces involved in the moons orbital motion around Earth. In the diagram, v represents the forward velocity of the moon, and a represents the acceleration due to gravity between Earth and the moon. The line encircling Earth shows the moons actual orbit, which results from the combination of v and a. | text | null |
L_0979 | ph concept | T_4703 | Acids are ionic compounds that produce positively charged hydrogen ions (H+ ) when dissolved in water. Acids taste sour and react with metals. Bases are ionic compounds that produce negatively charged hydroxide ions (OH ) when dissolved in water. Bases taste bitter and do not react with metals. Examples of acids are vinegar and battery acid. The acid in vinegar is weak enough to safely eat on a salad. The acid in a car battery is strong enough to eat through skin. Examples of bases include those in antacid tablets and drain cleaner. Bases in antacid tablets are weak enough to take for an upset stomach. Bases in drain cleaner are strong enough to cause serious burns. Q: What do you think causes these differences in the strength of acids and bases? A: The strength of an acid or a base depends on how much of it breaks down into ions when it dissolves in water. | text | null |
L_0979 | ph concept | T_4704 | The strength of an acid depends on how many hydrogen ions it produces when it dissolves in water. A stronger acid produces more hydrogen ions than a weaker acid. For example, sulfuric acid (H2 SO4 ), which is found in car batteries, is a strong acid because nearly all of it breaks down into ions when it dissolves in water. On the other hand, acetic acid (CH3 CO2 H), which is the acid in vinegar, is a weak acid because less than 1 percent of it breaks down into ions in water. The strength of a base depends on how many hydroxide ions it produces when it dissolves in water. A stronger base produces more hydroxide ions than a weaker base. For example, sodium hydroxide (NaOH), a base in drain cleaner, is a strong base because all of it breaks down into ions when it dissolves in water. Calcium carbonate (CaCO3 ), a base in antacids, is a weak base because only a small percentage of it breaks down into ions in water. | text | null |
L_0979 | ph concept | T_4705 | The strength of acids and bases is measured on a scale called the pH scale, which is shown in the Figure 1.1. By definition, pH represents the acidity, or hydrogen ion (H+ ) concentration, of a solution. Pure water, which is neutral, has a pH of 7. With a higher the concentration of hydrogen ions, a solution is more acidic and has a lower pH. Acids have a pH less than 7, and the strongest acids have a pH close to zero. Bases have a pH greater than 7, and the strongest bases have a pH close to 14. Its important to realize that the pH scale is based on powers of ten. For example, a solution with a pH of 8 is 10 times more basic than a solution with a pH of 7, and a solution with a pH of 9 is 100 times more basic than a solution with a pH of 7. Q: How much more acidic is a solution with a pH of 4 than a solution with a pH of 7? A: A solution with a pH of 4 is 1000 (10 10 10, or 103 ) times more acidic than a solution with a pH of 7. Q: Which solution on the pH scale in the Figure 1.1 is the weakest acid? Which solution is the strongest base? A: The weakest acid on the scale is milk, which has a pH value between 6.5 and 6.8. The strongest base on the scale is liquid drain cleaner, which has a pH of 14. | text | null |
L_0979 | ph concept | T_4706 | Acidity is an important factor for living things. For example, many plants grow best in soil that has a pH between 6 and 7. Fish may also need a pH between 6 and 7. Certain air pollutants form acids when dissolved in water droplets in the air. This results in acid fog and acid rain, which may have a pH of 4 or even lower. The pH chart in the Figure lowers the pH of surface waters such as ponds and lakes. As a result, the water may become too acidic for fish and other water organisms to survive. Acid fog and acid rain killed the trees in this forest. Even normal (clean) rain is somewhat acidic. Thats because carbon dioxide (CO2 ) in the air dissolves in raindrops, producing a weak acid called carbonic acid (H2 CO3 ), which has a pH of about 5.5. When rainwater soaks into the ground, it can slowly dissolve rocks, particularly those containing calcium carbonate. This is how water forms underground caves. Q: How do you think acid rain might affect buildings and statues made of stone? A: Acid rain dissolves and damages stone buildings and statues. The Figure 1.3 shows a statue that has been damaged by acid rain. | text | null |
L_0979 | ph concept | T_4706 | Acidity is an important factor for living things. For example, many plants grow best in soil that has a pH between 6 and 7. Fish may also need a pH between 6 and 7. Certain air pollutants form acids when dissolved in water droplets in the air. This results in acid fog and acid rain, which may have a pH of 4 or even lower. The pH chart in the Figure lowers the pH of surface waters such as ponds and lakes. As a result, the water may become too acidic for fish and other water organisms to survive. Acid fog and acid rain killed the trees in this forest. Even normal (clean) rain is somewhat acidic. Thats because carbon dioxide (CO2 ) in the air dissolves in raindrops, producing a weak acid called carbonic acid (H2 CO3 ), which has a pH of about 5.5. When rainwater soaks into the ground, it can slowly dissolve rocks, particularly those containing calcium carbonate. This is how water forms underground caves. Q: How do you think acid rain might affect buildings and statues made of stone? A: Acid rain dissolves and damages stone buildings and statues. The Figure 1.3 shows a statue that has been damaged by acid rain. | text | null |
L_0980 | photosynthesis reactions | T_4707 | Most of the energy used by living things comes either directly or indirectly from the sun. Thats because sunlight provides the energy for photosynthesis. This is the process in which plants and certain other organisms synthesize glucose (C6 H12 O6 ). The process uses carbon dioxide and water and also produces oxygen. The overall chemical equation for photosynthesis is: 6CO2 + 6H2 O + Light Energy C6 H12 O6 + 6O2 Photosynthesis changes light energy to chemical energy. The chemical energy is stored in the bonds of glucose molecules. Glucose, in turn, is used for energy by the cells of almost all living things. Photosynthetic organisms such as plants make their own glucose. Other organisms get glucose by consuming plants (or organisms that consume plants). Q: How do living things get energy from glucose? A: They break bonds in glucose and release the stored energy in the process of cellular respiration. | text | null |
L_0980 | photosynthesis reactions | T_4708 | The organisms pictured in the Figures 1.1, 1.2, and 1.3 all use sunlight to make glucose in the process of photo- synthesis. In addition to plants, they include bacteria and algae. All of these organisms contain the green pigment chlorophyll, which is needed to capture light energy. A tremendous amount of photosynthesis takes place in the plants of this lush tropi- cal rainforest. | text | null |
L_0980 | photosynthesis reactions | T_4708 | The organisms pictured in the Figures 1.1, 1.2, and 1.3 all use sunlight to make glucose in the process of photo- synthesis. In addition to plants, they include bacteria and algae. All of these organisms contain the green pigment chlorophyll, which is needed to capture light energy. A tremendous amount of photosynthesis takes place in the plants of this lush tropi- cal rainforest. | text | null |
L_0985 | position time graphs | T_4725 | The motion of an object can be represented by a position-time graph like Graph 1 in the Figure 1.1. In this type of graph, the y-axis represents position relative to the starting point, and the x-axis represents time. A position-time graph shows how far an object has traveled from its starting position at any given time since it started moving. Q: In the Figure 1.1, what distance has the object traveled from the starting point by the time 5 seconds have elapsed? A: The object has traveled a distance of 50 meters. | text | null |
L_0985 | position time graphs | T_4726 | In a position-time graph, the velocity of the moving object is represented by the slope, or steepness, of the graph line. If the graph line is horizontal, like the line after time = 5 seconds in Graph 2 in the Figure 1.2, then the slope is zero and so is the velocity. The position of the object is not changing. The steeper the line is, the greater the slope of the line is and the faster the objects motion is changing. | text | null |
L_0985 | position time graphs | T_4726 | In a position-time graph, the velocity of the moving object is represented by the slope, or steepness, of the graph line. If the graph line is horizontal, like the line after time = 5 seconds in Graph 2 in the Figure 1.2, then the slope is zero and so is the velocity. The position of the object is not changing. The steeper the line is, the greater the slope of the line is and the faster the objects motion is changing. | text | null |
L_0985 | position time graphs | T_4727 | Its easy to calculate the average velocity of a moving object from a position-time graph. Average velocity equals the change in position (represented by d) divided by the corresponding change in time (represented by t): velocity = d t For example, in Graph 2 in the Figure 1.2, the average velocity between 0 seconds and 5 seconds is: d t 25 m 0 m = 5 s0 s 25 m = 5s = 5 m/s velocity = | text | null |
L_0986 | potential energy | T_4728 | The diver has energy because of her position high above the pool. The type of energy she has is called potential energy. Potential energy is energy that is stored in a person or object. Often, the person or object has potential energy because of its position or shape. Q: What is it about the divers position that gives her potential energy? A: Because the diver is high above the water, she has the potential to fall toward Earth because of gravity. This gives her potential energy. | text | null |
L_0986 | potential energy | T_4729 | Potential energy due to the position of an object above Earths surface is called gravitational potential energy. Like the diver on the diving board, anything that is raised up above Earths surface has the potential to fall because of gravity. You can see another example of people with gravitational potential energy in the Figure 1.1. Gravitational potential energy depends on an objects weight and its height above the ground. It can be calculated with the equation: Gravitational potential energy (GPE) = weight height Consider the little girl on the sled, pictured in the Figure 1.1. She weighs 140 Newtons, and the top of the hill is 4 meters higher than the bottom of the hill. As she sits at the top of the hill, the childs gravitational potential energy is: GPE = 140 N 4 m = 560 N m Notice that the answer is given in Newton meters (N m), which is the SI unit for energy. A Newton meter is the energy needed to move a weight of 1 Newton over a distance of 1 meter. A Newton meter is also called a joule (J). Q: The gymnast on the balance beam pictured in the Figure 1.1 weighs 360 Newtons. If the balance beam is 1.2 meters above the ground, what is the gymnasts gravitational potential energy? A: Her gravitational potential energy is: GPE = 360 N 1.2 m = 432 N m, or 432 J | text | null |
L_0986 | potential energy | T_4730 | Potential energy due to an objects shape is called elastic potential energy. This energy results when an elastic object is stretched or compressed. The farther the object is stretched or compressed, the greater its potential energy is. A point will be reached when the object cant be stretched or compressed any more. Then it will forcefully return to its original shape. Look at the pogo stick in the Figure 1.2. Its spring has elastic potential energy when it is pressed down by the boys weight. When it cant be compressed any more, it will spring back to its original shape. The energy it releases will push the pogo stickand the boyoff the ground. Q: The girl in the Figure 1.3 is giving the elastic band of her slingshot potential energy by stretching it. Shes holding a small stone against the stretched band. What will happen when she releases the band? A: The elastic band will spring back to its original shape. When that happens, watch out! Some of the bands elastic potential energy will be transferred to the stone, which will go flying through the air. | text | null |
L_0986 | potential energy | T_4731 | All of the examples of potential energy described above involve movement or the potential to move. The form of energy that involves movement is called mechanical energy. Other forms of energy also involve potential energy, including chemical energy and nuclear energy. Chemical energy is stored in the bonds between the atoms of compounds. For example, food and batteries both contain chemical energy. Nuclear energy is stored in the nuclei of atoms because of the strong forces that hold the nucleus together. Nuclei of radioactive elements such as uranium are unstable, so they break apart and release the stored energy. | text | null |
L_0986 | potential energy | T_4731 | All of the examples of potential energy described above involve movement or the potential to move. The form of energy that involves movement is called mechanical energy. Other forms of energy also involve potential energy, including chemical energy and nuclear energy. Chemical energy is stored in the bonds between the atoms of compounds. For example, food and batteries both contain chemical energy. Nuclear energy is stored in the nuclei of atoms because of the strong forces that hold the nucleus together. Nuclei of radioactive elements such as uranium are unstable, so they break apart and release the stored energy. | text | null |
L_0987 | power | T_4732 | Power is a measure of the amount of work that can be done in a given amount of time. Power can be represented by the equation: Power = Work Time In this equation, work is measured in joules (J) and time is measured in seconds (s), so power is expressed in joules per second (J/s). This is the SI unit for power, also known as the watt (W). A watt equals 1 joule of work per second. Youre probably already familiar with watts. Light bulbs and small appliances such as microwave ovens are labeled with the watts of power they provide. For example, the package of light bulbs in the Figure 1.1 is labeled 14 watts. Q: Assume you have two light bulbs of the same type, such as two compact fluorescent light bulbs like the one pictured in the Figure 1.1. If one light bulb is a 25-watt bulb and the other is a 60-watt bulb, which bulb produces brighter light? A: The 60-watt bulb is more powerful, so it produces brighter light. Compared with a less powerful device, a more powerful device can either do more work in the same time or do the same work in less time. For example, compared with a low-power microwave oven, a high-power microwave oven can cook more food in the same time or the same amount of food in less time. | text | null |
L_0987 | power | T_4733 | Power can be calculated using the formula above if the amount of work and time are known. For example, assume that a microwave oven does 24,000 joules of work in 30 seconds. Then the power of the microwave is: 24000 J Power = Work Time = 30 s = 800 J/s, or 800 W Q: Another microwave oven does 5,000 joules of work in 5 seconds. What is its power? A: The power of the other microwave oven is: J Power = 5000 5 s = 1000 J/s, or 1000 W Q: Which microwave oven will heat the same amount of food in less time? A: The 1000-watt microwave oven has more power, so it will heat the same amount of food in less time. | text | null |
L_0987 | power | T_4734 | You can also calculate work if you know power and time by rewriting the power equation above as: Work = Power Time For example, if you use a 1000-watt microwave oven for 20 seconds, how much work does it do? First express 1000 watts in J/s and then substitute this value for power the work equation: Work = 1000 J/s 20 s = 20,000 J | text | null |
L_0987 | power | T_4735 | Sometimes power is measured in a unit called the horsepower. For example, the power of car engines is usually expressed in horsepowers. One horsepower is the amount of work a horse can do in 1 minute. It equals 745 watts of power. Compare the horsepowers in the Figure 1.2 to the other Figure 1.3. This team of three horses provides 3 horsepowers of power. This big tractor provides 180 horsepowers of power. Q: If the team of horses and the tractor do the same amount of work plowing a field, which will get the job done faster? A: The tractor will get the job done faster because it has more power. In fact, because the tractor has 30 times the power of the six-horse team, ideally it can do the same work 30 times faster! | text | null |
L_0987 | power | T_4735 | Sometimes power is measured in a unit called the horsepower. For example, the power of car engines is usually expressed in horsepowers. One horsepower is the amount of work a horse can do in 1 minute. It equals 745 watts of power. Compare the horsepowers in the Figure 1.2 to the other Figure 1.3. This team of three horses provides 3 horsepowers of power. This big tractor provides 180 horsepowers of power. Q: If the team of horses and the tractor do the same amount of work plowing a field, which will get the job done faster? A: The tractor will get the job done faster because it has more power. In fact, because the tractor has 30 times the power of the six-horse team, ideally it can do the same work 30 times faster! | text | null |
L_0989 | projectile motion | T_4741 | When the archer releases the bowstring, the arrow will be flung forward toward the top of the target where shes aiming. But another force will also act on the arrow in a different direction. The other force is gravity, and it will pull the arrow down toward Earth. The two forces combined will cause the arrow to move in the curved path shown in the Figure 1.1. This type of motion is called projectile motion. It occurs whenever an object curves down toward the ground because it has both a horizontal force and the downward force of gravity acting on it. Because of projectile motion, to hit the bulls eye of a target with an arrow, you actually have to aim for a spot above the bulls eye. You can see in theFigure 1.2 what happens if you aim at the bulls eye instead of above it. | text | null |
L_0989 | projectile motion | T_4742 | You can probably think of other examples of projectile motion. One is shown in the Figure 1.3. The cannon shoots a ball straight ahead, giving it horizontal motion. At the same time, gravity pulls the ball down toward the ground. Q: How would you show the force of gravity on the cannon ball in the Figure 1.3? A: You would add a line pointing straight down from the cannon to the ground. | text | null |
L_0989 | projectile motion | T_4742 | You can probably think of other examples of projectile motion. One is shown in the Figure 1.3. The cannon shoots a ball straight ahead, giving it horizontal motion. At the same time, gravity pulls the ball down toward the ground. Q: How would you show the force of gravity on the cannon ball in the Figure 1.3? A: You would add a line pointing straight down from the cannon to the ground. | text | null |
L_0989 | projectile motion | T_4742 | You can probably think of other examples of projectile motion. One is shown in the Figure 1.3. The cannon shoots a ball straight ahead, giving it horizontal motion. At the same time, gravity pulls the ball down toward the ground. Q: How would you show the force of gravity on the cannon ball in the Figure 1.3? A: You would add a line pointing straight down from the cannon to the ground. | text | null |
L_0990 | properties of acids | T_4743 | Acids are ionic compounds that produce positive hydrogen ions (H+ ) when dissolved in water. Ionic compounds are compounds that contain positive metal ions and negative nonmetal ions held together by ionic bonds. (Ions are atoms that have become charged particles by gaining or losing electrons.) An example of an acid is hydrogen chloride (HCl). When it dissolves in water, it separates into positive hydrogen ions and negative chloride ions (Cl ). This is represented by the chemical equation: H O 2 HCl H+ + Cl | text | null |
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