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L_1041 | synthesis reactions | T_4903 | A synthesis reaction occurs when two or more reactants combine to form a single product. A synthesis reaction can be represented by the general equation: A+BC In this equation, the letters A and B represent the reactants that begin the reaction, and the letter C represents the product that is synthesized in the reaction. The arrow shows the direction in which the reaction occurs. Q: What is the chemical equation for the synthesis of nitrogen dioxide (NO2 ) from nitric oxide (NO) and oxygen (O2 )? A: The equation for this synthesis reaction is: 2NO + O2 2NO2 | text | null |
L_1041 | synthesis reactions | T_4904 | Another example of a synthesis reaction is the combination of sodium (Na) and chlorine (Cl) to produce sodium chloride (NaCl). This reaction is represented by the chemical equation: 2Na + Cl2 2NaCl Sodium is a highly reactive metal, and chlorine is a poisonous gas. Both elements are pictured in the Figure 1.1. The compound they synthesize has very different properties. Sodium chloride is commonly called table salt, which is neither reactive nor poisonous. In fact, salt is a necessary component of the human diet. | text | null |
L_1042 | technological design constraints | T_4905 | The development of new technologywhether its a simple kite or a complex machineis called technological design. The technological design process is a step-by-step approach to finding a solution to a problem. Often, the main challenge in technological design is finding a solution that works within the constraints, or limits, on the design. All technological designs have constraints. Q: Assume you want to design a kite. What might be some constraints on your design? A: Possible constraints might include the shape and size of the kite and the materials you use to make it. | text | null |
L_1042 | technological design constraints | T_4906 | Technological design constraints may be physical or social. Physical design constraints include factors such as natural laws and properties of materials. A kite, for example, will fly only if its shape allows air currents to lift it. Otherwise, gravity will keep it on the ground. Social design constraints include factors such as ease of use, safety, attractiveness, and cost. For example, a kite string should be easy to unwind as the wind carries the kite higher. | text | null |
L_1042 | technological design constraints | T_4907 | All technological designs have trade-offs because no design is perfect. For example, a design might be very good at solving a problem, but it might be too expensive to be practical. Or a design might be very attractive, but it might not be safe to use. Choosing the best design often involves weighing the pros and cons of different options and deciding which ones are most important. Q: What trade-offs might there be on the design of a kite? A: You might want to make a big kite, but if its too big it might be too heavy. Then it would fly only on very windy days. Or you might want to make a kite using a certain material that you really like, but the material might cost more than you can afford to spend. | text | null |
L_1045 | technology and society | T_4913 | Important new technologies such as the wheel have had a big impact on human society. Major advances in technol- ogy have influenced every aspect of life, including transportation, food production, manufacturing, communication, medicine, and the arts. Thats because technology has the goal of solving human problems, so new technologies usually make life better. They may make work easier, for example, or make people healthier. Sometimes, however, new technologies affect people in negative ways. For example, using a new product or process might cause human health problems or pollute the environment. Q: Can you think of a modern technology that has both positive and negative effects on people? A: Modern methods of transportation have both positive and negative effects on people. They help people and goods move quickly all over the world. However, most of them pollute the environment. For example, gasoline-powered cars and trucks add many pollutants to the atmosphere. The pollutants harm peoples health and contribute to global climate change. | text | null |
L_1045 | technology and society | T_4914 | Few technologies have impacted society as greatly as the powerful steam engine developed by Scottish inventor James Watt in 1775 (see Figure 1.1). Watts steam engine was soon being used to power all kinds of machines. It started a revolution in industry. For the first time in history, people did not have to rely on human or animal muscle, wind, or water for power. With the steam engine to power machines, new factories sprang up all over Britain. The Industrial Revolution began in Britain the late 1700s. It eventually spread throughout Western Europe, North America, Japan, and many other countries. It marked a major turning point in human history. Almost every aspect of daily life was influenced by it in some way. Average income and population both began to grow faster than ever before. People flocked to the new factories for jobs, and densely populated towns and cities grew up around the factories. The new towns and cities were crowded, and soot from the factories polluted the air. You can see an example of this in the Figure 1.2. This made living conditions very poor. Working conditions in the factories were also bad, with long hours and the pace set by machines. Even young children worked in the factories, damaging their health and giving them little opportunity for education or play. Q: In addition to factory machines, the steam engine was used to power farm machinery, trains, and ships. What effects might this have had on peoples lives? A: Farm machinery replaced human labor and allowed fewer people to produce more food. This is why many rural people migrated to the new towns and cities to look for work in factories. Steam-powered trains and ships made it easier for people to migrate. Food and factory goods could also be transported on steam-powered trains and ships, making them available to far more people. | text | null |
L_1048 | thermal conductors and insulators | T_4920 | Conduction is the transfer of thermal energy between particles of matter that are touching. Thermal conduction occurs when particles of warmer matter bump into particles of cooler matter and transfer some of their thermal energy to the cooler particles. Conduction is usually faster in certain solids and liquids than in gases. Materials that are good conductors of thermal energy are called thermal conductors. Metals are especially good thermal conductors because they have freely moving electrons that can transfer thermal energy quickly and easily. Besides the heating element inside a toaster, another example of a thermal conductor is a metal radiator, like the one in the Figure 1.1. When hot water flows through the coils of the radiator, the metal quickly heats up by conduction and then radiates thermal energy into the surrounding air. Q: Thermal conductors have many uses, but sometimes its important to prevent the transfer of thermal energy. Can you think of an example? A: One example is staying warm on a cold day. You will stay warmer if you can prevent the transfer of your own thermal energy to the outside air. | text | null |
L_1048 | thermal conductors and insulators | T_4921 | One way to retain your own thermal energy on a cold day is to wear clothes that trap air. Thats because air, like other gases, is a poor conductor of thermal energy. The particles of gases are relatively far apart, so they dont bump into each other or into other things as often as the more closely spaced particles of liquids or solids. Therefore, particles of gases have fewer opportunities to transfer thermal energy. Materials that are poor thermal conductors are called thermal insulators. Down-filled snowsuits, like those in the Figure 1.2, are good thermal insulators because their feather filling traps a lot of air. Another example of a thermal insulator is pictured in the Figure 1.3. The picture shows fluffy pink insulation inside the attic of a home. Like the down filling in a snowsuit, the insulation traps a lot of air. The insulation helps to prevent the transfer of thermal energy into the house on hot days and out of the house on cold days. Other materials that are thermal insulators include plastic and wood. Thats why pot handles and cooking utensils are often made of these materials. Notice that the outside of the toaster pictured in the opening image is made of plastic. The plastic casing helps prevent the transfer of thermal energy from the heating element inside to the outer surface of the toaster where it could cause burns. Q: Thermal insulators have many practical uses besides the uses mentioned above. Can you think of others? A: Thermal insulators are often used to keep food or drinks hot or cold. For example, Styrofoam coolers and thermos containers are used for these purposes. | text | null |
L_1048 | thermal conductors and insulators | T_4921 | One way to retain your own thermal energy on a cold day is to wear clothes that trap air. Thats because air, like other gases, is a poor conductor of thermal energy. The particles of gases are relatively far apart, so they dont bump into each other or into other things as often as the more closely spaced particles of liquids or solids. Therefore, particles of gases have fewer opportunities to transfer thermal energy. Materials that are poor thermal conductors are called thermal insulators. Down-filled snowsuits, like those in the Figure 1.2, are good thermal insulators because their feather filling traps a lot of air. Another example of a thermal insulator is pictured in the Figure 1.3. The picture shows fluffy pink insulation inside the attic of a home. Like the down filling in a snowsuit, the insulation traps a lot of air. The insulation helps to prevent the transfer of thermal energy into the house on hot days and out of the house on cold days. Other materials that are thermal insulators include plastic and wood. Thats why pot handles and cooking utensils are often made of these materials. Notice that the outside of the toaster pictured in the opening image is made of plastic. The plastic casing helps prevent the transfer of thermal energy from the heating element inside to the outer surface of the toaster where it could cause burns. Q: Thermal insulators have many practical uses besides the uses mentioned above. Can you think of others? A: Thermal insulators are often used to keep food or drinks hot or cold. For example, Styrofoam coolers and thermos containers are used for these purposes. | text | null |
L_1049 | thermal energy | T_4922 | Why do the air and sand of Death Valley feel so hot? Its because their particles are moving very rapidly. Anything that is moving has kinetic energy, and the faster it is moving, the more kinetic energy it has. The total kinetic energy of moving particles of matter is called thermal energy. Its not just hot things such as the air and sand of Death Valley that have thermal energy. All matter has thermal energy, even matter that feels cold. Thats because the particles of all matter are in constant motion and have kinetic energy. | text | null |
L_1049 | thermal energy | T_4923 | Thermal energy and temperature are closely related. Both reflect the kinetic energy of moving particles of matter. However, temperature is the average kinetic energy of particles of matter, whereas thermal energy is the total kinetic energy of particles of matter. Does this mean that matter with a lower temperature has less thermal energy than matter with a higher temperature? Not necessarily. Another factor also affects thermal energy. The other factor is mass. Q: Look at the pot of soup and the tub of water in the Figure 1.1. Which do you think has greater thermal energy? A: The soup is boiling hot and has a temperature of 100 C, whereas the water in the tub is just comfortably warm, with a temperature of about 38 C. Although the water in the tub has a much lower temperature, it has greater thermal energy. The particles of soup have greater average kinetic energy than the particles of water in the tub, explaining why the soup has a higher temperature. However, the mass of the water in the tub is much greater than the mass of the soup in the pot. This means that there are many more particles of water than soup. All those moving particles give the water in the tub greater total kinetic energy, even though their average kinetic energy is less. Therefore, the water in the tub has greater thermal energy than the soup. Q: Could a block of ice have more thermal energy than a pot of boiling water? A: Yes, the block of ice could have more thermal energy if its mass was much greater than the mass of the boiling water. | text | null |
L_1050 | thermal radiation | T_4924 | The bonfire from the opening image has a lot of thermal energy. Thermal energy is the total kinetic energy of moving particles of matter, and the transfer of thermal energy is called heat. Thermal energy from the bonfire is transferred to the hands by thermal radiation. Thermal radiation is the transfer of thermal energy by waves that can travel through air or even through empty space, as shown in the Figure 1.1. When the waves of thermal energy reach objects, they transfer the energy to the objects, causing them to warm up. This is how the fire warms the hands of someone sitting near the bonfire. This is also how the suns energy reaches Earth and heats its surface. Without the energy radiated from the sun, Earth would be too cold to support life as we know it. Thermal radiation is one of three ways that thermal energy can be transferred. The other two ways are conduction and convection, both of which need matter to transfer energy. Radiation is the only way of transferring thermal energy that doesnt require matter. | text | null |
L_1050 | thermal radiation | T_4925 | You might be surprised to learn that everything radiates thermal energy, not just really hot things such as the sun or a fire. For example, when its cold outside, a heated home radiates some of its thermal energy into the outdoor environment. A home that is poorly insulated radiates more energy than a home that is well insulated. Special cameras can be used to detect radiated heat. In the Figure 1.2, you can see an image created by one of these cameras. The areas that are yellow are the areas where the greatest amount of thermal energy is radiating from the home. Even people radiate thermal energy. In fact, when a room is full of people, it may feel noticeably warmer because of all the thermal energy the people radiate! Q: Where is thermal radiation radiating from the home in the picture? A: The greatest amount of thermal energy is radiating from the window on the upper left. A lot of thermal energy is also radiating from the edges of the windows and door. | text | null |
L_1051 | thomsons atomic model | T_4926 | John Dalton discovered atoms in 1804. He thought they were the smallest particles of matter, which could not be broken down into smaller particles. He envisioned them as solid, hard spheres. It wasnt until 1897 that a scientist named Joseph John (J. J.) Thomson discovered that there are smaller particles within the atom. Thomson was born in England and studied at Cambridge University, where he later became a professor. In 1906, he won the Nobel Prize in physics for his research on how gases conduct electricity. This research also led to his discovery of the electron. You can see a picture of Thomson 1.1. | text | null |
L_1051 | thomsons atomic model | T_4927 | In his research, Thomson passed current through a cathode ray tube, similar to the one seen in the Figure 1.2. A cathode ray tube is a glass tube from which virtually all of the air has been removed. It contains a piece of metal called an electrode at each end. One electrode is negatively charged and known as a cathode. The other electrode is positively charged and known as an anode. When high-voltage electric current is applied to the end plates, a cathode ray travels from the cathode to the anode. What is a cathode ray? Thats what Thomson wanted to know. Is it just a ray of energy that travels in waves like a ray of light? That was one popular hypothesis at the time. Or was a cathode ray a stream of moving particles? That was the other popular hypothesis. Thomson tested these ideas by placing negative and positive plates along the sides of the cathode ray tube to see how the cathode ray would be affected. The cathode ray appeared to be repelled by the negative plate and attracted by the positive plate. This meant that the ray was negative in charge and that is must consist of particles that have mass. He called the particles corpuscles, but they were later renamed electrons. Thomson also measured the mass of the particles he had identified. He did this by determining how much the cathode rays were bent when he varied the voltage. He found that the mass of the particles was 2000 times smaller than the mass of the smallest atom, the hydrogen atom. In short, Thomson had discovered the existence of particles smaller than atoms. This disproved Daltons claim that atoms are the smallest particles of matter. From his discovery, Thomson also inferred that electrons are fundamental particles within atoms. Q: Atoms are neutral in electric charge. How can they be neutral if they contain negatively charged electrons? A: Atoms also contain positively charged particles that cancel out the negative charge of the electrons. However, these positive particles werent discovered until a couple of decades after Thomson discovered electrons. | text | null |
L_1051 | thomsons atomic model | T_4927 | In his research, Thomson passed current through a cathode ray tube, similar to the one seen in the Figure 1.2. A cathode ray tube is a glass tube from which virtually all of the air has been removed. It contains a piece of metal called an electrode at each end. One electrode is negatively charged and known as a cathode. The other electrode is positively charged and known as an anode. When high-voltage electric current is applied to the end plates, a cathode ray travels from the cathode to the anode. What is a cathode ray? Thats what Thomson wanted to know. Is it just a ray of energy that travels in waves like a ray of light? That was one popular hypothesis at the time. Or was a cathode ray a stream of moving particles? That was the other popular hypothesis. Thomson tested these ideas by placing negative and positive plates along the sides of the cathode ray tube to see how the cathode ray would be affected. The cathode ray appeared to be repelled by the negative plate and attracted by the positive plate. This meant that the ray was negative in charge and that is must consist of particles that have mass. He called the particles corpuscles, but they were later renamed electrons. Thomson also measured the mass of the particles he had identified. He did this by determining how much the cathode rays were bent when he varied the voltage. He found that the mass of the particles was 2000 times smaller than the mass of the smallest atom, the hydrogen atom. In short, Thomson had discovered the existence of particles smaller than atoms. This disproved Daltons claim that atoms are the smallest particles of matter. From his discovery, Thomson also inferred that electrons are fundamental particles within atoms. Q: Atoms are neutral in electric charge. How can they be neutral if they contain negatively charged electrons? A: Atoms also contain positively charged particles that cancel out the negative charge of the electrons. However, these positive particles werent discovered until a couple of decades after Thomson discovered electrons. | text | null |
L_1051 | thomsons atomic model | T_4928 | Thomson also knew that atoms are neutral in electric charge, so he asked the same question: How can atoms contain negative particles and still be neutral? He hypothesized that the rest of the atom must be positively charged in order to cancel out the negative charge of the electrons. He envisioned the atom as being similar to a plum pudding, like the one pictured in the Figure 1.3mostly positive in charge (the pudding) with negative electrons (the plums) scattered through it. Q: How is our modern understanding of atomic structure different from Thomsons plum pudding model? A: Today we know that all of the positive charge in an atom is concentrated in a tiny central area called the nucleus, with the electrons swirling through empty space around it, as in the Figure 1.4. The nucleus was discovered just a few years after Thomson discovered the electron, so the plum pudding model was soon rejected. | text | null |
L_1052 | transfer of electric charge | T_4929 | The girl pictured above became negatively charged because electrons flowed from the van de Graaff generator to her. Whenever electrons are transferred between objects, neutral matter becomes charged. This occurs even with individual atoms. Atoms are neutral in electric charge because they have the same number of negative electrons as positive protons. However, if atoms lose or gain electrons, they become charged particles called ions. You can see how this happens in the Figure 1.1. When an atom loses electrons, it becomes a positively charged ion, or cation. When an atom gains electrons, it becomes a negative charged ion, or anion. | text | null |
L_1052 | transfer of electric charge | T_4930 | Like the formation of ions, the formation of charged matter in general depends on the transfer of electrons, either between two materials or within a material. Three ways this can occur are referred to as conduction, polarization, and friction. All three ways are described below. However, regardless of how electrons are transferred, the total charge always remains the same. Electrons move, but they arent destroyed. This is the law of conservation of charge. | text | null |
L_1052 | transfer of electric charge | T_4931 | The transfer of electrons from the van de Graaff generator to the man is an example of conduction. Conduction occurs when there is direct contact between materials that differ in their ability to give up or accept electrons. A van de Graff generator produces a negative charge on its dome, so it tends to give up electrons. Human hands are positively charged, so they tend to accept electrons. Therefore, electrons flow from the dome to the mans hand when they are in contact. You dont need a van de Graaff generator for conduction to take place. It may occur when you walk across a wool carpet in rubber-soled shoes. Wool tends to give up electrons and rubber tends to accept them. Therefore, the carpet transfers electrons to your shoes each time you put down your foot. The transfer of electrons results in you becoming negatively charged and the carpet becoming positively charged. | text | null |
L_1052 | transfer of electric charge | T_4932 | Assume that you have walked across a wool carpet in rubber-soled shoes and become negatively charged. If you then reach out to touch a metal doorknob, electrons in the neutral metal will be repelled and move away from your hand before you even touch the knob. In this way, one end of the doorknob becomes positively charged and the other end becomes negatively charged. This is called polarization. Polarization occurs whenever electrons within a neutral object move because of the electric field of a nearby charged object. It occurs without direct contact between the two objects. The Figure 1.2 models how polarization occurs. Q: What happens when the negatively charged plastic rod in the diagram is placed close to the neutral metal plate? A: Electrons in the plate are repelled by the positive charges in the rod. The electrons move away from the rod, causing one side of the plate to become positively charged and the other side to become negatively charged. | text | null |
L_1052 | transfer of electric charge | T_4933 | Did you ever rub an inflated balloon against your hair? You can see what happens in the Figure 1.3. Friction between the balloon and hair cause electrons from the hair to rub off on the balloon. Thats because a balloon attracts electrons more strongly than hair does. After the transfer of electrons, the balloon becomes negatively charged and the hair becomes positively charged. The individual hairs push away from each other and stand on end because like charges repel each other. The balloon and the hair attract each other because opposite charges attract. Electrons are transferred in this way whenever there is friction between materials that differ in their ability to give up or accept electrons. Q: If you rub a balloon against a wall, it may stick to the wall. Explain why. | text | null |
L_1053 | transition metals | T_4934 | Transition metals are all the elements in groups 3-12 of the periodic table. In the periodic table pictured in Figure known elements. In addition to copper (Cu), well known examples of transition metals include iron (Fe), zinc (Zn), silver (Ag), and gold (Au) (Copper (Cu) is pictured in its various applications in the opening image). Q: Transition metals have been called the most typical of all metals. What do you think this means? A: Unlike some other metals, transition metals have the properties that define the metals class. They are excellent conductors of electricity, for example, and they also have luster, malleability, and ductility. You can read more about these properties of transition metals below. | text | null |
L_1053 | transition metals | T_4935 | Transition metals are superior conductors of heat as well as electricity. They are malleable, which means they can be shaped into sheets, and ductile, which means they can be shaped into wires. They have high melting and boiling points, and all are solids at room temperature, except for mercury (Hg), which is a liquid. Transition metals are also high in density and very hard. Most of them are white or silvery in color, and they are generally lustrous, or shiny. The compounds that transition metals form with other elements are often very colorful. You can see several examples in the Figure 1.2. Some properties of transition metals set them apart from other metals. Compared with the alkali metals in group 1 and the alkaline Earth metals in group 2, the transition metals are much less reactive. They dont react quickly with water or oxygen, which explains why they resist corrosion. Q: How is the number of valence electrons typically related to the properties of elements? A: The number of valence electrons usually determines how reactive elements are as well as the ways in which they react with other elements. | text | null |
L_1053 | transition metals | T_4935 | Transition metals are superior conductors of heat as well as electricity. They are malleable, which means they can be shaped into sheets, and ductile, which means they can be shaped into wires. They have high melting and boiling points, and all are solids at room temperature, except for mercury (Hg), which is a liquid. Transition metals are also high in density and very hard. Most of them are white or silvery in color, and they are generally lustrous, or shiny. The compounds that transition metals form with other elements are often very colorful. You can see several examples in the Figure 1.2. Some properties of transition metals set them apart from other metals. Compared with the alkali metals in group 1 and the alkaline Earth metals in group 2, the transition metals are much less reactive. They dont react quickly with water or oxygen, which explains why they resist corrosion. Q: How is the number of valence electrons typically related to the properties of elements? A: The number of valence electrons usually determines how reactive elements are as well as the ways in which they react with other elements. | text | null |
L_1053 | transition metals | T_4936 | Transition metals include the elements that are most often placed below the periodic table (the pink- and purple- shaded elements in the Figure 1.1). Those that follow lanthanum (La) are called lanthanides. They are all relatively reactive for transition metals. Those that follow actinium (Ac) are called actinides. They are all radioactive. This means that they are unstable, so they decay into different, more stable elements. Many of the actinides do not occur in nature but are made in laboratories. | text | null |
L_1054 | transverse wave | T_4937 | A transverse wave is a wave in which particles of the medium vibrate at right angles, or perpendicular, to the direction that the wave travels. Another example of a transverse wave is the wave that passes through a rope with you shake one end of the rope up and down, as in the Figure 1.1. The direction of the wave is down the length of the rope away from the hand. The rope itself moves up and down as the wave passes through it. Click image to the left or use the URL below. URL: Q: When a guitar string is plucked, in what direction does the wave travel? In what directions does the string vibrate? A: The wave travels down the string to the end. The string vibrates up and down at right angles to the direction of the wave. | text | null |
L_1054 | transverse wave | T_4938 | A transverse wave is characterized by the high and low points reached by particles of the medium as the wave passes through. The high points are called crests, and the low points are called troughs. You can see both in the Figure below. | text | null |
L_1054 | transverse wave | T_4939 | Transverse waves called S waves occur during earthquakes. The disturbance that causes an earthquake sends transverse waves through underground rocks in all directions away from the disturbance. S waves may travel for hundreds of miles. An S wave is modeled in the Figure 1.3. | text | null |
L_1055 | types of friction | T_4940 | Friction is the force that opposes motion between any surfaces that are in contact. There are four types of friction: static, sliding, rolling, and fluid friction. Static, sliding, and rolling friction occur between solid surfaces. Fluid friction occurs in liquids and gases. All four types of friction are described below. | text | null |
L_1055 | types of friction | T_4941 | Static friction acts on objects when they are resting on a surface. For example, if you are hiking in the woods, there is static friction between your shoes and the trail each time you put down your foot (see Figure 1.1). Without this static friction, your feet would slip out from under you, making it difficult to walk. In fact, thats exactly what happens if you try to walk on ice. Thats because ice is very slippery and offers very little friction. Q: Can you think of other examples of static friction? A: One example is the friction that helps the people climb the rock wall in the opening picture above. Static friction keeps their hands and feet from slipping. | text | null |
L_1055 | types of friction | T_4942 | Sliding friction is friction that acts on objects when they are sliding over a surface. Sliding friction is weaker than static friction. Thats why its easier to slide a piece of furniture over the floor after you start it moving than it is to get it moving in the first place. Sliding friction can be useful. For example, you use sliding friction when you write with a pencil. The pencil lead slides easily over the paper, but theres just enough friction between the pencil and paper to leave a mark. Q: How does sliding friction help you ride a bike? A: There is sliding friction between the brake pads and bike rims each time you use your bikes brakes. This friction slows the rolling wheels so you can stop. | text | null |
L_1055 | types of friction | T_4943 | Rolling friction is friction that acts on objects when they are rolling over a surface. Rolling friction is much weaker than sliding friction or static friction. This explains why most forms of ground transportation use wheels, including bicycles, cars, 4-wheelers, roller skates, scooters, and skateboards. Ball bearings are another use of rolling friction. You can see what they look like in the Figure 1.2. They let parts of a wheel or other machine roll rather than slide over on another. The ball bearings in this wheel reduce friction between the inner and outer cylinders when they turn. | text | null |
L_1055 | types of friction | T_4944 | Fluid friction is friction that acts on objects that are moving through a fluid. A fluid is a substance that can flow and take the shape of its container. Fluids include liquids and gases. If youve ever tried to push your open hand through the water in a tub or pool, then youve experienced fluid friction. You can feel the resistance of the water against your hand. Look at the skydiver in the Figure 1.3. Hes falling toward Earth with a parachute. Resistance of the air against the parachute slows his descent. The faster or larger a moving object is, the greater is the fluid friction resisting its motion. Thats why there is greater air resistance against the parachute than the skydivers body. | text | null |
L_1056 | ultrasound | T_4945 | Ultrasound is sound that has a wave frequency higher than the human ear can detect. It includes all sound with wave frequencies higher than 20,000 waves per second, or 20,000 hertz (Hz). Although we cant hear ultrasound, it is very useful to humans and some other animals. Uses of ultrasound include echolocation, sonar, and ultrasonography. | text | null |
L_1056 | ultrasound | T_4946 | Animals such as bats and dolphins send out ultrasound waves and use their echoes, or reflected waves, to identify the locations of objects they cannot see. This is called echolocation. Animals use echolocation to find prey and avoid running into objects in the dark. You can see in the Figure 1.1 how a bat uses echolocation to find insect prey. | text | null |
L_1056 | ultrasound | T_4947 | Sonar uses ultrasound in a way that is similar to echolocation. Sonar stands for sound navigation and ranging. It is used to locate underwater objects such as submarines. Thats how the ship pictured in the Figure 1.2 is using it. A sonar device is both a sender and a receiver. It sends out ultrasound waves and detects the waves after they reflect from underwater objects. The distance to underwater objects can be calculated from the known speed of sound in water and the time it takes for the sound waves to travel to the object. The equation for distance traveled when speed and time are known is: Distance = Speed Time Consider the ship and submarine pictured in the Figure 1.2. If an ultrasound wave travels from the ship to the submarine and back again in 2 seconds, what is the distance from the ship to the submarine? The sound wave travels from the ship to the submarine in just 1 second, or half the time it takes to make the round trip. The speed of sound waves through ocean water is 1437 m/s. Therefore, the distance from the ship to the submarine is: Q: Now assume that the sonar device on the ship sends an ultrasound wave to the bottom of the water. If the sound wave is reflected back to the device in 4 seconds, how deep is the water? A: The time it takes the wave to reach the bottom is 2 seconds. So the distance from the ship to the bottom of the water is: Distance = 1437 m/s 2 s = 2874 m | text | null |
L_1056 | ultrasound | T_4947 | Sonar uses ultrasound in a way that is similar to echolocation. Sonar stands for sound navigation and ranging. It is used to locate underwater objects such as submarines. Thats how the ship pictured in the Figure 1.2 is using it. A sonar device is both a sender and a receiver. It sends out ultrasound waves and detects the waves after they reflect from underwater objects. The distance to underwater objects can be calculated from the known speed of sound in water and the time it takes for the sound waves to travel to the object. The equation for distance traveled when speed and time are known is: Distance = Speed Time Consider the ship and submarine pictured in the Figure 1.2. If an ultrasound wave travels from the ship to the submarine and back again in 2 seconds, what is the distance from the ship to the submarine? The sound wave travels from the ship to the submarine in just 1 second, or half the time it takes to make the round trip. The speed of sound waves through ocean water is 1437 m/s. Therefore, the distance from the ship to the submarine is: Q: Now assume that the sonar device on the ship sends an ultrasound wave to the bottom of the water. If the sound wave is reflected back to the device in 4 seconds, how deep is the water? A: The time it takes the wave to reach the bottom is 2 seconds. So the distance from the ship to the bottom of the water is: Distance = 1437 m/s 2 s = 2874 m | text | null |
L_1056 | ultrasound | T_4948 | Another use of ultrasound is to see inside the human body. This use of ultrasound is called ultrasonography. Harmless ultrasound waves are sent inside the body, and the reflected waves are used to create an image on a screen. This technology is used to examine internal organs and unborn babies without risk to the patient. You can see a doctor using ultrasound in the Figure 1.3. | text | null |
L_1057 | unsaturated hydrocarbons | T_4949 | Hydrocarbons are compounds that contain only carbon and hydrogen. The carbon atoms in hydrocarbons may share single, double, or triple covalent bonds. Unsaturated hydrocarbons contain at least one double or triple bond between carbon atoms. They are classified on the basis of their bonds as alkenes, aromatic hydrocarbons, or alkynes. Q: Why do you suppose hydrocarbons with double or triple bonds are called unsaturated? A: A carbon atom always forms four covalent bonds. Carbon atoms with double or triple bonds are unable to bond with as many hydrogen atoms as they could if they were joined only by single bonds. This makes them unsaturated with hydrogen atoms. | text | null |
L_1057 | unsaturated hydrocarbons | T_4950 | Unsaturated hydrocarbons that contain one or more double bonds are called alkenes. The name of a specific alkene always ends in -ene and has a prefix indicating the number of carbon atoms. The structural formula in the Figure Ethene is produced by most fruits and vegetables. It speeds up ripening. The Figure 1.1 show the effects of ethene on bananas. Alkenes can have different shapes. They can form straight chains, branched chains, or rings. Alkenes with the same atoms but different shapes are called isomers. Smaller alkenes have relatively high boiling and melting points, so they are gases at room temperature. Larger alkenes have lower boiling and melting points, so they are liquids or waxy solids at room temperature. The bananas on the left were stored in a special bag that absorbs ethene. The bananas on the right were stored without a bag. | text | null |
L_1057 | unsaturated hydrocarbons | T_4951 | Unsaturated hydrocarbons called aromatic hydrocarbons are cyclic hydrocarbons that have double bonds. These compounds have six carbon atoms in a ring with alternating single and double bonds. The smallest aromatic hydrocarbon is benzene, which has just one ring. Its structural formula is shown in the Figure 1.2. Larger aromatic hydrocarbons consist of two or more rings, which are joined together by bonds between their carbon atoms. The name of aromatic hydrocarbons comes from their strong aroma, or scent. Thats why they are used in air fresheners and mothballs. A: Each carbon atom forms four covalent bonds. Carbon atoms always form four covalent bonds, regardless of the atoms to which it bonds. | text | null |
L_1057 | unsaturated hydrocarbons | T_4952 | Unsaturated hydrocarbons that contain one or more triple bonds are called alkynes. The names of specific alkynes always end in -yne and have a prefix for the number of carbon atoms. The structural formula in the Figure 1.3 represents the smallest alkyne, named ethyne, which has two carbon atoms and two hydrogen atoms (C2 H2 ). Ethyne is also called acetylene. It is burned in acetylene torches, like the one pictured in the Figure 1.4. The flame of an acetylene torch is so hot that it can melt metal. Cutting metal with an acetylene (ethyne) torch. Alkynes may form straight or branched chains. They rarely occur in ring shapes. In fact, alkynes of all shapes are relatively rare in nature. | text | null |
L_1057 | unsaturated hydrocarbons | T_4952 | Unsaturated hydrocarbons that contain one or more triple bonds are called alkynes. The names of specific alkynes always end in -yne and have a prefix for the number of carbon atoms. The structural formula in the Figure 1.3 represents the smallest alkyne, named ethyne, which has two carbon atoms and two hydrogen atoms (C2 H2 ). Ethyne is also called acetylene. It is burned in acetylene torches, like the one pictured in the Figure 1.4. The flame of an acetylene torch is so hot that it can melt metal. Cutting metal with an acetylene (ethyne) torch. Alkynes may form straight or branched chains. They rarely occur in ring shapes. In fact, alkynes of all shapes are relatively rare in nature. | text | null |
L_1058 | using earths magnetic field | T_4953 | Like a bar magnet, planet Earth has north and south magnetic poles and a magnetic field over which it exerts magnetic force. Earths magnetic field is called the magnetosphere. You can see it in the Figure 1.1. | text | null |
L_1058 | using earths magnetic field | T_4954 | The sun gives off radiation in solar winds. You can see solar winds in the Figure 1.1. Notice what happens to solar winds when they reach the magnetosphere. They are deflected almost completely by Earths magnetic field. Radiation in solar wind would wash over Earth and kill most living things were it not for the magnetosphere. It protects Earths organisms from radiation like an umbrella protects you from rain. Q: Now can you explain the northern lights? A: Energetic particles in solar wind collide with atoms in the atmosphere over the poles, and energy is released in the form of light. The swirling patterns of light follow lines of magnetic force in the magnetosphere. | text | null |
L_1058 | using earths magnetic field | T_4955 | Another benefit of Earths magnetic field is its use for navigation. People use compasses to detect Earths magnetic north pole and tell direction. Many animals have natural compasses that work just as well. For example, the loggerhead turtle in the Figure 1.2 senses the direction and strength of Earths magnetic field and uses it to navigate along migration routes. Many migratory bird species can also sense the magnetic field and use it for navigation. Recent research suggests that they may have structures in their eyes that let them see Earths magnetic field as a visual pattern. | text | null |
L_1059 | valence electrons | T_4956 | Valence electrons are the electrons in the outer energy level of an atom that can participate in interactions with other atoms. Valence electrons are generally the electrons that are farthest from the nucleus. As a result, they may be attracted as much or more by the nucleus of another atom than they are by their own nucleus. | text | null |
L_1059 | valence electrons | T_4957 | Because valence electrons are so important, atoms are often represented by simple diagrams that show only their valence electrons. These are called electron dot diagrams, and three are shown below. In this type of diagram, an elements chemical symbol is surrounded by dots that represent the valence electrons. Typically, the dots are drawn as if there is a square surrounding the element symbol with up to two dots per side. An element never has more than eight valence electrons, so there cant be more than eight dots per atom. Q: Carbon (C) has four valence electrons. What does an electron dot diagram for this element look like? A: An electron dot diagram for carbon looks like this: | text | null |
L_1059 | valence electrons | T_4958 | The number of valence electrons in an atom is reflected by its position in the periodic table of the elements (see the periodic table in the Figure 1.1). Across each row, or period, of the periodic table, the number of valence electrons in groups 1-2 and 13-18 increases by one from one element to the next. Within each column, or group, of the table, all the elements have the same number of valence electrons. This explains why all the elements in the same group have very similar chemical properties. For elements in groups 1-2 and 13-18, the number of valence electrons is easy to tell directly from the periodic table. This is illustrated in the simplified periodic table in the Figure 1.2. It shows just the numbers of valence electrons in each of these groups. For elements in groups 3-12, determining the number of valence electrons is more complicated. Q: Based on both periodic tables above (Figures 1.1 and 1.2), what are examples of elements that have just one valence electron? What are examples of elements that have eight valence electrons? How many valence electrons does oxygen (O) have? A: Any element in group 1 has just one valence electron. Examples include hydrogen (H), lithium (Li), and sodium (Na). Any element in group 18 has eight valence electrons (except for helium, which has a total of just two electrons). Examples include neon (Ne), argon (Ar), and krypton (Kr). Oxygen, like all the other elements in group 16, has six valence electrons. | text | null |
L_1059 | valence electrons | T_4959 | The table salt pictured in the Figure 1.3 contains two elements that are so reactive they are rarely found alone in nature. Instead, they undergo chemical reactions with other elements and form compounds. Table salt is the compound named sodium chloride (NaCl). It forms when an atom of sodium (Na) gives up an electron and an atom of chlorine (Cl) accepts it. When this happens, sodium becomes a positively charged ion (Na+ ), and chlorine becomes a negatively charged ion (Cl ). The two ions are attracted to each and join a matrix of interlocking sodium and chloride ions, forming a crystal of salt. Q: Why does sodium give up an electron? A: An atom of a group 1 element such as sodium has just one valence electron. It is eager to give up this electron in order to have a full outer energy level, because this will give it the most stable arrangement of electrons. You can see how this happens in the animation at the following URL and in the Figure 1.4. Group 2 elements with two valence electrons are almost as reactive as elements in group 1 for the same reason. Q: Why does chlorine accept the electron from sodium? A: An atom of a group 17 element such as chlorine has seven valence electrons. It is eager to gain an extra electron to fill its outer energy level and gain stability. Group 16 elements with six valence electrons are almost as reactive for the same reason. Atoms of group 18 elements have eight valence electrons (or two in the case of helium). These elements already have a full outer energy level, so they are very stable. As a result, they rarely if ever react with other elements. Elements in other groups vary in their reactivity but are generally less reactive than elements in groups 1, 2, 16, or 17. Q: Find calcium (Ca) in the periodic table (see Figure 1.1). Based on its position in the table, how reactive do you think calcium is? Name another element with which calcium might react. A: Calcium is a group 2 element with two valence electrons. Therefore, it is very reactive and gives up electrons in chemical reactions. It is likely to react with an element with six valence electrons that wants to gain two electrons. This would be an element in group 6, such as oxygen. Table salt (sodium chloride). | text | null |
L_1059 | valence electrons | T_4959 | The table salt pictured in the Figure 1.3 contains two elements that are so reactive they are rarely found alone in nature. Instead, they undergo chemical reactions with other elements and form compounds. Table salt is the compound named sodium chloride (NaCl). It forms when an atom of sodium (Na) gives up an electron and an atom of chlorine (Cl) accepts it. When this happens, sodium becomes a positively charged ion (Na+ ), and chlorine becomes a negatively charged ion (Cl ). The two ions are attracted to each and join a matrix of interlocking sodium and chloride ions, forming a crystal of salt. Q: Why does sodium give up an electron? A: An atom of a group 1 element such as sodium has just one valence electron. It is eager to give up this electron in order to have a full outer energy level, because this will give it the most stable arrangement of electrons. You can see how this happens in the animation at the following URL and in the Figure 1.4. Group 2 elements with two valence electrons are almost as reactive as elements in group 1 for the same reason. Q: Why does chlorine accept the electron from sodium? A: An atom of a group 17 element such as chlorine has seven valence electrons. It is eager to gain an extra electron to fill its outer energy level and gain stability. Group 16 elements with six valence electrons are almost as reactive for the same reason. Atoms of group 18 elements have eight valence electrons (or two in the case of helium). These elements already have a full outer energy level, so they are very stable. As a result, they rarely if ever react with other elements. Elements in other groups vary in their reactivity but are generally less reactive than elements in groups 1, 2, 16, or 17. Q: Find calcium (Ca) in the periodic table (see Figure 1.1). Based on its position in the table, how reactive do you think calcium is? Name another element with which calcium might react. A: Calcium is a group 2 element with two valence electrons. Therefore, it is very reactive and gives up electrons in chemical reactions. It is likely to react with an element with six valence electrons that wants to gain two electrons. This would be an element in group 6, such as oxygen. Table salt (sodium chloride). | text | null |
L_1059 | valence electrons | T_4959 | The table salt pictured in the Figure 1.3 contains two elements that are so reactive they are rarely found alone in nature. Instead, they undergo chemical reactions with other elements and form compounds. Table salt is the compound named sodium chloride (NaCl). It forms when an atom of sodium (Na) gives up an electron and an atom of chlorine (Cl) accepts it. When this happens, sodium becomes a positively charged ion (Na+ ), and chlorine becomes a negatively charged ion (Cl ). The two ions are attracted to each and join a matrix of interlocking sodium and chloride ions, forming a crystal of salt. Q: Why does sodium give up an electron? A: An atom of a group 1 element such as sodium has just one valence electron. It is eager to give up this electron in order to have a full outer energy level, because this will give it the most stable arrangement of electrons. You can see how this happens in the animation at the following URL and in the Figure 1.4. Group 2 elements with two valence electrons are almost as reactive as elements in group 1 for the same reason. Q: Why does chlorine accept the electron from sodium? A: An atom of a group 17 element such as chlorine has seven valence electrons. It is eager to gain an extra electron to fill its outer energy level and gain stability. Group 16 elements with six valence electrons are almost as reactive for the same reason. Atoms of group 18 elements have eight valence electrons (or two in the case of helium). These elements already have a full outer energy level, so they are very stable. As a result, they rarely if ever react with other elements. Elements in other groups vary in their reactivity but are generally less reactive than elements in groups 1, 2, 16, or 17. Q: Find calcium (Ca) in the periodic table (see Figure 1.1). Based on its position in the table, how reactive do you think calcium is? Name another element with which calcium might react. A: Calcium is a group 2 element with two valence electrons. Therefore, it is very reactive and gives up electrons in chemical reactions. It is likely to react with an element with six valence electrons that wants to gain two electrons. This would be an element in group 6, such as oxygen. Table salt (sodium chloride). | text | null |
L_1059 | valence electrons | T_4959 | The table salt pictured in the Figure 1.3 contains two elements that are so reactive they are rarely found alone in nature. Instead, they undergo chemical reactions with other elements and form compounds. Table salt is the compound named sodium chloride (NaCl). It forms when an atom of sodium (Na) gives up an electron and an atom of chlorine (Cl) accepts it. When this happens, sodium becomes a positively charged ion (Na+ ), and chlorine becomes a negatively charged ion (Cl ). The two ions are attracted to each and join a matrix of interlocking sodium and chloride ions, forming a crystal of salt. Q: Why does sodium give up an electron? A: An atom of a group 1 element such as sodium has just one valence electron. It is eager to give up this electron in order to have a full outer energy level, because this will give it the most stable arrangement of electrons. You can see how this happens in the animation at the following URL and in the Figure 1.4. Group 2 elements with two valence electrons are almost as reactive as elements in group 1 for the same reason. Q: Why does chlorine accept the electron from sodium? A: An atom of a group 17 element such as chlorine has seven valence electrons. It is eager to gain an extra electron to fill its outer energy level and gain stability. Group 16 elements with six valence electrons are almost as reactive for the same reason. Atoms of group 18 elements have eight valence electrons (or two in the case of helium). These elements already have a full outer energy level, so they are very stable. As a result, they rarely if ever react with other elements. Elements in other groups vary in their reactivity but are generally less reactive than elements in groups 1, 2, 16, or 17. Q: Find calcium (Ca) in the periodic table (see Figure 1.1). Based on its position in the table, how reactive do you think calcium is? Name another element with which calcium might react. A: Calcium is a group 2 element with two valence electrons. Therefore, it is very reactive and gives up electrons in chemical reactions. It is likely to react with an element with six valence electrons that wants to gain two electrons. This would be an element in group 6, such as oxygen. Table salt (sodium chloride). | text | null |
L_1059 | valence electrons | T_4960 | Valence electrons also determine how wellif at allthe atoms of an element conduct electricity. The copper wires in the cable in the Figure 1.5 are coated with plastic. Copper is an excellent conductor of electricity, so it is used for wires that carry electric current. Plastic contains mainly carbon, which cannot conduct electricity, so it is used as insulation on the wires. Q: Why do copper and carbon differ in their ability to conduct electricity? A: Atoms of metals such as copper easily give up valence electrons. Their electrons can move freely and carry electric current. Atoms of nonmetals such as the carbon, on the other hand, hold onto their electrons. Their electrons cant move freely and carry current. A few elements, called metalloids, can conduct electricity, but not as well as metals. Examples include silicon and germanium in group 14. Both become better conductors at higher temperatures. These elements are called semiconductors. Q: How many valence electrons do atoms of silicon and germanium have? What happens to their valence electrons when the atoms are exposed to an electric field? A: Atoms of these two elements have four valence electrons. When the atoms are exposed to an electric field, the valence electrons move away from the atoms and allow current to flow. | text | null |
L_1060 | velocity | T_4961 | Speed tells you only how fast or slow an object is moving. It doesnt tell you the direction the object is moving. The measure of both speed and direction is called velocity. Velocity is a vector. A vector is measurement that includes both size and direction. Vectors are often represented by arrows. When using an arrow to represent velocity, the length of the arrow stands for speed, and the way the arrow points indicates the direction. Click image to the left or use the URL below. URL: | text | null |
L_1060 | velocity | T_4962 | The arrows in the Figure 1.1 represent the velocity of three different objects. Arrows A and B are the same length but point in different directions. They represent objects moving at the same speed but in different directions. Arrow C is shorter than arrow A or B but points in the same direction as arrow A. It represents an object moving at a slower speed than A or B but in the same direction as A. | text | null |
L_1060 | velocity | T_4963 | Objects have the same velocity only if they are moving at the same speed and in the same direction. Objects moving at different speeds, in different directions, or both have different velocities. Look again at arrows A and B from the Figure 1.1. They represent objects that have different velocities only because they are moving in different directions. A and C represent objects that have different velocities only because they are moving at different speeds. Objects represented by B and C have different velocities because they are moving in different directions and at different speeds. Q: Jerod is riding his bike at a constant speed. As he rides down his street he is moving from east to west. At the end of the block, he turns right and starts moving from south to north, but hes still traveling at the same speed. Has his velocity changed? A: Although Jerods speed hasnt changed, his velocity has changed because he is moving in a different direction. Q: How could you use vector arrows to represent Jerods velocity and how it changes? A: The arrows might look like this: | text | null |
L_1060 | velocity | T_4964 | You can calculate the average velocity of a moving object that is not changing direction by dividing the distance the object travels by the time it takes to travel that distance. You would use this formula: velocity = distance time This is the same formula that is used for calculating average speed. It represents velocity only if the answer also includes the direction that the object is traveling. Lets work through a sample problem. Tonis dog is racing down the sidewalk toward the east. The dog travels 36 meters in 18 seconds before it stops running. The velocity of the dog is: distance time 36 m = 18 s = 2 m/s east velocity = Note that the answer is given in the SI unit for velocity, which is m/s, and it includes the direction that the dog is traveling. Q: What would the dogs velocity be if it ran the same distance in the opposite direction but covered the distance in 24 seconds? A: In this case, the velocity would be: distance time 36 m = 24 s = 1.5 m/s west velocity = | text | null |
L_1061 | velocity time graphs | T_4965 | The changing velocity of the sprinteror of any other moving person or objectcan be represented by a velocity- time graph like the one in the Figure 1.1 for the sprinter. A velocity-time graph shows how velocity changes over time. The sprinters velocity increases for the first 4 seconds of the race, it remains constant for the next 3 seconds, and it decreases during the last 3 seconds after she crosses the finish line. | text | null |
L_1061 | velocity time graphs | T_4966 | In a velocity-time graph, acceleration is represented by the slope, or steepness, of the graph line. If the line slopes upward, like the line between 0 and 4 seconds in the Figure 1.1, velocity is increasing, so acceleration is positive. If the line is horizontal, as it is between 4 and 7 seconds, velocity is constant and acceleration is zero. If the line slopes downward, like the line between 7 and 10 seconds, velocity is decreasing and acceleration is negative. Negative acceleration is called deceleration. Q: Assume that another sprinter is running the same race. The other runner reaches a top velocity of 9 m/s by 4 seconds after the start of the race. How would the first 4 seconds of the velocity-time graph for this runner be different from the Figure 1.1? A: The graph line for this runner during seconds 0-4 would be steeper (have a greater slope). This would show that acceleration is greater during this time period for the other sprinter. | text | null |
L_1062 | visible light and matter | T_4967 | Reflection of light occurs when light bounces back from a surface that it cannot pass through. Reflection may be regular or diffuse. If the surface is very smooth, like a mirror, the reflected light forms a very clear image. This is called regular, or specular, reflection. In the Figure 1.1, the smooth surface of the still water in the pond on the left reflects light in this way. When light is reflected from a rough surface, the waves of light are reflected in many different directions, so a clear image does not form. This is called diffuse reflection. In the Figure 1.1, the ripples in the water in the picture on the right cause diffuse reflection of the blooming trees. | text | null |
L_1062 | visible light and matter | T_4968 | Transmission of light occurs when light passes through matter. As light is transmitted, it may pass straight through matter or it may be refracted or scattered as it passes through. When light is refracted, it changes direction as it passes into a new medium and changes speed. The straw in the Figure 1.2 looks bent where light travels from water to air. Light travels more quickly in air than in water and changes direction. Scattering occurs when light bumps into tiny particles of matter and spreads out in all directions. In the Figure air, giving the headlights a halo appearance. Q: What might be another example of light scattering? A: When light passes through smoky air, it is scattered by tiny particles of soot. | text | null |
L_1062 | visible light and matter | T_4968 | Transmission of light occurs when light passes through matter. As light is transmitted, it may pass straight through matter or it may be refracted or scattered as it passes through. When light is refracted, it changes direction as it passes into a new medium and changes speed. The straw in the Figure 1.2 looks bent where light travels from water to air. Light travels more quickly in air than in water and changes direction. Scattering occurs when light bumps into tiny particles of matter and spreads out in all directions. In the Figure air, giving the headlights a halo appearance. Q: What might be another example of light scattering? A: When light passes through smoky air, it is scattered by tiny particles of soot. | text | null |
L_1062 | visible light and matter | T_4969 | Light may transfer its energy to matter rather than being reflected or transmitted by matter. This is called absorption. When light is absorbed, the added energy increases the temperature of matter. If you get into a car that has been sitting in the sun all day, the seats and other parts of the cars interior may be almost too hot to touch, especially if they are black or very dark in color. Thats because dark colors absorb most of the sunlight that strikes them. Q: In hot sunny climates, people often dress in light-colored clothes. Why is this a good idea? A: Light-colored clothes absorb less light and reflect more light than dark-colored clothes, so they keep people cooler. | text | null |
L_1062 | visible light and matter | T_4970 | Matter can be classified on the basis of its interactions with light. Matter may be transparent, translucent, or opaque. An example of each type of matter is pictured in the Figure 1.4. Transparent matter is matter that transmits light without scattering it. Examples of transparent matter include air, pure water, and clear glass. You can see clearly through transparent objects, such as the top panes of the window 1.4, because just about all of the light that strikes them passes through to the other side. Translucent matter is matter that transmits light but scatters the light as it passes through. Light passes through translucent objects but you cannot see clearly through them because the light is scattered in all directions. The frosted glass panes at the bottom of the window 1.4 are translucent. Opaque matter is matter that does not let any light pass through it. Matter may be opaque because it absorbs light, reflects light, or does some combination of both. Examples of opaque objects are objects made of wood, like the shutters in the Figure 1.5. The shutters absorb most of the light that strikes them and reflect just a few wavelengths of visible light. The glass mirror 1.5 is also opaque. Thats because it reflects all of the light that strikes it. | text | null |
L_1062 | visible light and matter | T_4970 | Matter can be classified on the basis of its interactions with light. Matter may be transparent, translucent, or opaque. An example of each type of matter is pictured in the Figure 1.4. Transparent matter is matter that transmits light without scattering it. Examples of transparent matter include air, pure water, and clear glass. You can see clearly through transparent objects, such as the top panes of the window 1.4, because just about all of the light that strikes them passes through to the other side. Translucent matter is matter that transmits light but scatters the light as it passes through. Light passes through translucent objects but you cannot see clearly through them because the light is scattered in all directions. The frosted glass panes at the bottom of the window 1.4 are translucent. Opaque matter is matter that does not let any light pass through it. Matter may be opaque because it absorbs light, reflects light, or does some combination of both. Examples of opaque objects are objects made of wood, like the shutters in the Figure 1.5. The shutters absorb most of the light that strikes them and reflect just a few wavelengths of visible light. The glass mirror 1.5 is also opaque. Thats because it reflects all of the light that strikes it. | text | null |
L_1063 | vision and the eye | T_4971 | The human eye is an organ that is specialized to collect light and focus images. The structures of the human eye are shown in the Figure 1.1. Examine each structure in the diagram as you read about it below. The sclera, also known as the white of the eye, is an opaque outer covering that protects the eye. It keeps light out of the eye except at the center front of the eye. The cornea is a transparent outer covering of the front of the eye. It protects the eye and also acts as a convex lens. A convex lens is thicker in the middle than at the edges and makes rays of light converge, or meet at a point. The shape of the cornea helps focus light that enters the eye. The pupil is an opening in the front of the eye. It looks black because it doesnt reflect any light. All the light passes through it instead. The pupil controls the amount of light that enters the eye. It automatically gets bigger or smaller to let more or less light in as needed. The iris is the colored part of the eye. It controls the size of the pupil. The lens of the eye is a convex lens. It fine-tunes the focus so an image forms on the retina at the back of the eye. Tiny muscles control the shape of the lens to focus images of close or distant objects. The retina is a membrane lining the back of the eye. The retina has nerve cells called rods and cones that change images to electrical signals. Rods are good at sensing dim light but cant distinguish different colors of light. Cones can sense colors but not dim light. There are three different types of cones. Each type senses one of the three primary colors of light (red, green, or blue). The optic nerve carries electrical signals from the rods and cones to the brain. Q: The lens of the eye is a convex lens. How would vision be affected if the lens of the eye was concave instead of convex? A: A concave lens causes rays of light to diverge, or spread apart. It forms a virtual image on the same side of the lens at the object being viewed. Therefore, a concave lens would focus the image in front of the eye, not on the retina inside the eye. No signals would be sent to the brain so vision would not be possible. | text | null |
L_1063 | vision and the eye | T_4972 | The ability to see is called vision. This ability depends on more than healthy eyes. It also depends on certain parts of the brain, because the brain and eyes work together to allow us to see. The eyes collect and focus visible light. The lens and other structures of the eye work together to focus an image on the retina. The image is upside-down and reduced in size, as you can see in the Figure 1.2. Cells in the retina change the image to electrical signals that travel to the brain through the optic nerve. The brain interprets the electrical signals as shape, color, and brightness. It also interprets the image as though it were right-side up. The brain does this automatically, so what we see always appears right-side up. The brain also interprets what we are seeing. Q: The part of the brain that processes information from the eyes is the visual cortex. It is located at the back of the brain. How might an injury to the visual cortex affect vision? A: An injury to the visual cortex might cause abnormal vision or even blindness regardless of how well the eyes can gather and focus light. | text | null |
L_1064 | vision problems and corrective lenses | T_4973 | Many people have problems with their vision, or ability to see. Often, the problem is due to the shape of the eyes and how they focus light. Two of the most common vision problems are nearsightedness and farsightedness, which you can read about below. You may even have one of these vision problems yourself. Usually, the problems can be corrected with contact lenses or lenses in eyeglasses. In many people, they can also be corrected with laser surgery, which reshapes the outer layer of the eye. Click image to the left or use the URL below. URL: | text | null |
L_1064 | vision problems and corrective lenses | T_4974 | Nearsightedness, or myopia, is the condition in which nearby objects are seen clearly, but distant objects appear blurry. The Figure 1.1 shows how it occurs. The eyeball is longer (from front to back) than normal. This causes images to be focused in front of the retina instead of on the retina. Myopia can be corrected with concave lenses. The lenses focus images farther back in the eye, so they fall on the retina instead of in front of it. Q: Sometimes squinting the eyes can help someone see more clearly. Why do you think this works? A: Squinting may improve focus by slightly changing the shape of the eyes. When you squint, you tighten muscles around the eyes, putting pressure on the eyeballs. | text | null |
L_1064 | vision problems and corrective lenses | T_4975 | Farsightedness, or hyperopia, is the condition in which distant objects are seen clearly, but nearby objects appear blurry. It occurs when the eyeball is shorter than normal (see Figure 1.2). This causes images to be focused in a spot that would fall behind the retina (if light could pass through the retina). Hyperopia can be corrected with convex lenses. The lenses focus images farther forward in the eye, so they fall on the retina instead of behind it. Q: Joey has hyperopia. When is he more likely to need his glasses: when he reads a book or when he watches TV? A: With hyperopia, Joey is farsighted. He can probably see the TV more clearly than the words in a book because the TV is farther away. Therefore, he is more likely to need his glasses when he reads than when he watches TV. | text | null |
L_1065 | wave amplitude | T_4976 | Waves that travel through mattersuch as the fabric of a flagare called mechanical waves. The matter they travel through is called the medium. When the energy of a wave passes through the medium, particles of the medium move. The more energy the wave has, the farther the particles of the medium move. The distance the particles move is measured by the waves amplitude. | text | null |
L_1065 | wave amplitude | T_4977 | Wave amplitude is the maximum distance the particles of the medium move from their resting positions when a wave passes through. The resting position of a particle of the medium is where the particle would be in the absence of a wave. The Figure 1.1 show the amplitudes of two different types of waves: transverse and longitudinal waves. In a transverse wave, particles of the medium move up and down at right angles to the direction of the wave. Wave amplitude of a transverse wave is the difference in height between the crest and the resting position. The crest is the highest point particles of the medium reach. The higher the crests are, the greater the amplitude of the wave. In a longitudinal wave, particles of the medium move back and forth in the same direction as the wave. Wave amplitude of a longitudinal wave is the distance between particles of the medium where it is compressed by the wave. The closer together the particles are, the greater the amplitude of the wave. Q: What do you think determines a waves amplitude? A: Wave amplitude is determined by the energy of the disturbance that causes the wave. | text | null |
L_1065 | wave amplitude | T_4978 | A wave caused by a disturbance with more energy has greater amplitude. Imagine dropping a small pebble into a pond of still water. Tiny ripples will move out from the disturbance in concentric circles. The ripples are low- amplitude waves with very little energy. Now imagine throwing a big boulder into the pond. Very large waves will be generated by the disturbance. These waves are high-amplitude waves and have a great deal of energy. | text | null |
L_1066 | wave frequency | T_4979 | The number of waves that pass a fixed point in a given amount of time is wave frequency. Wave frequency can be measured by counting the number of crests (high points) of waves that pass the fixed point in 1 second or some other time period. The higher the number is, the greater the frequency of the waves. The SI unit for wave frequency is the hertz (Hz), where 1 hertz equals 1 wave passing a fixed point in 1 second. The Figure 1.1 shows high-frequency and low-frequency transverse waves. Q: The wavelength of a wave is the distance between corresponding points on adjacent waves. For example, it is the distance between two adjacent crests in the transverse waves in the diagram. Infer how wave frequency is related to wavelength. | text | null |
L_1066 | wave frequency | T_4980 | The frequency of a wave is the same as the frequency of the vibrations that caused the wave. For example, to generate a higher-frequency wave in a rope, you must move the rope up and down more quickly. This takes more energy, so a higher-frequency wave has more energy than a lower-frequency wave with the same amplitude. You can see examples of different frequencies in the Figure 1.2 (Amplitude is the distance that particles of the medium move when the energy of a wave passes through them.) | text | null |
L_1067 | wave interactions | T_4981 | Atoms are the building blocks of matter. Unlike blocks that we know, these building blocks are incredibly small. In fact, they are the smallest particles of an element. Atoms still have the same properties as the elements they make up. For example, an atom of gold has the same melting point as a gold coin. If we could see it, it would have the same color. Elements are also pure substances. This means they are not mixed with anything else. Pure substances such as nickel, hydrogen, and helium make up all kinds of matter. All the atoms of a given element are identical. Atoms of different elements are not physically the same. Think of something you might have made from LEGOs. You built some shape using the many different sized and shaped blocks. This is much like how atoms combine to become everything we know. If we took only one size and shape of block and put them together, we would make a pure substance. It would be an element. If you take apart anything that you have built, those individual parts are like the atoms. With those small parts, you build bigger things. Sometimes they are all the same type of block. Other times, they may be different kinds of blocks. We use these combinations of different blocks to make more complicated things. | text | null |
L_1067 | wave interactions | T_4982 | Unlike LEGO bricks, atoms are extremely small. The radius of an atom is well under 1 nanometer. Thats one- billionth of a meter. Such a number is hard to imagine. Consider this: trillions of atoms would fit inside the period at the end of this sentence. In other words, atoms are way too small to be seen with the naked eye. | text | null |
L_1067 | wave interactions | T_4983 | Although atoms are very tiny, they consist of even smaller particles. Atoms are made of protons, neutrons, and electrons: Protons have a positive charge. Electrons have a negative charge. Neutrons are neutral in charge. | text | null |
L_1067 | wave interactions | T_4984 | Figure below represents a simple model of an atom. Models help scientists make sense of things. Perhaps they are either too big or too small. Maybe they are just too complicated to make sense of. This simple model helps scientists think about the atom. Is this how the atom really looks? Not exactly! Remember, a model helps us make sense of things. They may not be an exact copy of the object. You will learn about more complex models of atoms in the coming years, but this model is a good place to start. | text | null |
L_1067 | wave interactions | T_4985 | At the center of an atom is the nucleus (plural, nuclei). The nucleus contains most of the atoms mass. However, in size, its just a tiny part of the atom. The model in Figure above is not to scale. If an atom were the size of a football stadium, the nucleus would be only about the size of a pea. The nucleus, in turn, consists of two types of particles, called protons and neutrons. These particles are tightly packed inside the nucleus. Constantly moving about the nucleus are other particles called electrons. | text | null |
L_1067 | wave interactions | T_4986 | A proton is a particle inside the nucleus of an atom. It has a positive electric charge. All protons are identical. It is all about the number of protons in the atoms. The number of protons is what gives the atoms of different elements their unique properties. Atoms of each type of element have a characteristic number of protons. For example, each atom of carbon has six protons (see Figure below ). No two elements have atoms with the same number of protons. | text | null |
L_1067 | wave interactions | T_4987 | A neutron is a particle inside the nucleus of an atom. It has no electric charge. Atoms of an element often have the same number of neutrons as protons. For example, most carbon atoms have six neutrons as well as six protons. This is also shown in Figure below . | text | null |
L_1067 | wave interactions | T_4988 | An electron is a particle outside the nucleus of an atom. It has a negative electric charge. The charge of an electron is opposite but equal to the charge of a proton. Atoms have the same number of electrons as protons. As a result, the negative and positive charges "cancel out." This makes atoms electrically neutral. For example, a carbon atom has six electrons that "cancel out" its six protons. | text | null |
L_1067 | wave interactions | T_4989 | By clicking a link below, you will leave the CK-12 site and open an external site in a new tab. This page will remain open in the original tab. | text | null |
L_1068 | wave interference | T_4990 | When two or more waves meet, they interact with each other. The interaction of waves with other waves is called wave interference. Wave interference may occur when two waves that are traveling in opposite directions meet. The two waves pass through each other, and this affects their amplitude. Amplitude is the maximum distance the particles of the medium move from their resting positions when a wave passes through. How amplitude is affected by wave interference depends on the type of interference. Interference can be constructive or destructive. | text | null |
L_1068 | wave interference | T_4991 | Constructive interference occurs when the crests, or highest points, of one wave overlap the crests of the other wave. You can see this in the Figure 1.1. As the waves pass through each other, the crests combine to produce a wave with greater amplitude. | text | null |
L_1068 | wave interference | T_4992 | Destructive interference occurs when the crests of one wave overlap the troughs, or lowest points, of another wave. The Figure 1.2 shows what happens. As the waves pass through each other, the crests and troughs cancel each other out to produce a wave with zero amplitude. | text | null |
L_1068 | wave interference | T_4993 | Waves may reflect off an obstacle that they are unable to pass through. When waves are reflected straight back from an obstacle, the reflected waves interfere with the original waves and create standing waves. These are waves that appear to be standing still. Standing waves occur because of a combination of constructive and destructive interference. Q: How could you use a rope to produce standing waves? A: You could tie one end of the rope to a fixed object, such as doorknob, and move the other end up and down to generate waves in the rope. When the waves reach the fixed object, they are reflected back. The original waves and the reflected waves interfere to produce a standing wave. Try it yourself and see if the waves appear to stand still. | text | null |
L_1069 | wave particle theory | T_4994 | Electromagnetic radiation, commonly called light, is the transfer of energy by waves called electromagnetic waves. These waves consist of vibrating electric and magnetic fields. Where does electromagnetic energy come from? It is released when electrons return to lower energy levels in atoms. Electromagnetic radiation behaves like continuous waves of energy most of the time. Sometimes, however, electromagnetic radiation seems to behave like discrete, or separate, particles rather than waves. So does electromagnetic radiation consist of waves or particles? | text | null |
L_1069 | wave particle theory | T_4995 | This question about the nature of electromagnetic radiation was debated by scientists for more than two centuries, starting in the 1600s. Some scientists argued that electromagnetic radiation consists of particles that shoot around like tiny bullets. Other scientists argued that electromagnetic radiation consists of waves, like sound waves or water waves. Until the early 1900s, most scientists thought that electromagnetic radiation is either one or the other and that scientists on the other side of the argument were simply wrong. Q: Do you think electromagnetic radiation is a wave or a particle? A: Heres a hint: it may not be a question of either-or. Keep reading to learn more. | text | null |
L_1069 | wave particle theory | T_4996 | In 1905, the physicist Albert Einstein developed a new theory about electromagnetic radiation. The theory is often called the wave-particle theory. It explains how electromagnetic radiation can behave as both a wave and a particle. Einstein argued that when an electron returns to a lower energy level and gives off electromagnetic energy, the energy is released as a discrete packet of energy. We now call such a packet of energy a photon. According to Einstein, a photon resembles a particle but moves like a wave. You can see this in the Figure 1.1. The theory posits that waves of photons traveling through space or matter make up electromagnetic radiation. | text | null |
L_1069 | wave particle theory | T_4997 | A photon isnt a fixed amount of energy. Instead, the amount of energy in a photon depends on the frequency of the electromagnetic wave. The frequency of a wave is the number of waves that pass a fixed point in a given amount of time, such as the number of waves per second. In waves with higher frequencies, photons have more energy. | text | null |
L_1069 | wave particle theory | T_4998 | After Einstein proposed his theory, evidence was discovered to support it. For example, scientists shone laser light through two slits in a barrier made of a material that blocked light. You can see the setup of this type of experiment in the Figure 1.2. Using a special camera that was very sensitive to light, they took photos of the light that passed through the slits. The photos revealed tiny pinpoints of light passing through the double slits. This seemed to show that light consists of particles. However, if the camera was exposed to the light for a long time, the pinpoints accumulated in bands that resembled interfering waves. Therefore, the experiment showed that light seems to consist of particles that act like waves. | text | null |
L_1070 | wave speed | T_4999 | Wave speed is the distance a wave travels in a given amount of time, such as the number of meters it travels per second. Wave speed (and speed in general) can be represented by the equation: Speed = Distance Time | text | null |
L_1070 | wave speed | T_5000 | Wave speed is related to both wavelength and wave frequency. Wavelength is the distance between two correspond- ing points on adjacent waves. Wave frequency is the number of waves that pass a fixed point in a given amount of time. This equation shows how the three factors are related: Speed = Wavelength x Wave Frequency In this equation, wavelength is measured in meters and frequency is measured in hertz (Hz), or number of waves per second. Therefore, wave speed is given in meters per second, which is the SI unit for speed. Q: If you increase the wavelength of a wave, does the speed of the wave increase as well? A: Increasing the wavelength of a wave doesnt change its speed. Thats because when wavelength increases, wave frequency decreases. As a result, the product of wavelength and wave frequency is still the same speed. Click image to the left or use the URL below. URL: | text | null |
L_1070 | wave speed | T_5001 | The equation for wave speed can be used to calculate the speed of a wave when both wavelength and wave frequency are known. Consider an ocean wave with a wavelength of 3 meters and a frequency of 1 hertz. The speed of the wave is: Speed = 3 m x 1 wave/s = 3 m/s Q: Kim made a wave in a spring by pushing and pulling on one end. The wavelength is 0.1 m, and the wave frequency is 2 hertz. What is the speed of the wave? A: Substitute these values into the equation for speed: Speed = 0.1 m x 2 waves/s = 0.2 m/s | text | null |
L_1070 | wave speed | T_5002 | The equation for wave speed (above) can be rewritten as: Frequency = Speed Wavelength or Wavelength = Speed Frequency Therefore, if you know the speed of a wave and either the wavelength or wave frequency, you can calculate the missing value. For example, suppose that a wave is traveling at a speed of 2 meters per second and has a wavelength of 1 meter. Then the frequency of the wave is: Frequency = 2m/s 1m = 2 waves/s, or 2 Hz Q: A wave is traveling at a speed of 2 m/s and has a frequency of 2 Hz. What is its wavelength? A: Substitute these values into the equation for wavelength: Wavelength = 2m/s 2waves/s =1m | text | null |
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