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L_0733 | machines | T_3639 | An exoskeleton suit may seem like science fiction, turning ordinary humans into super heroes. But wearable robots are moving forward into reality. And for paraplegics, the ability to stand and walk that these machines provide is a super power. QUEST meets Austin Whitney and Tamara Mena, two "Exoskeleton Test Pilots" who are now putting this new technology through its paces. For more information on exoskeleton suits, see http://science.kqed.org/ques MEDIA Click image to the left or use the URL below. URL: | text | null |
L_0733 | machines | T_3640 | You read above that machines do not increase the work done on an object. In other words, you cant get more work out of a machine than you put into it. In fact, machines always do less work on the object than the user does on the machine. Thats because all machines must use some of the work put into them to overcome friction. How much work? It depends on the efficiency of the machine. Efficiency is the percent of input work that becomes output work. It is a measure of how well a machine reduces friction. | text | null |
L_0733 | machines | T_3641 | Consider the ramp in Figure 16.11. Its easier to push the heavy piece of furniture up the ramp to the truck than to lift it straight up off the ground. However, pushing the furniture over the surface of the ramp creates a lot of friction. Some of the force applied to moving the furniture must be used to overcome the friction. It would be more efficient to use a dolly on wheels to roll the furniture up the ramp. Thats because rolling friction is much less than sliding friction. As a result, the efficiency of the ramp would be greater with a dolly. | text | null |
L_0733 | machines | T_3642 | Efficiency can be calculated with the equation: Efficiency = Output work 100% Input work Consider a machine that puts out 6000 joules of work. To produce that much work from the machine requires the user to put in 8000 joules of work. To find the efficiency of the machine, substitute these values into the equation for efficiency: Efficiency = 6000 J 100% = 75% 8000 J You Try It! Problem: Rani puts 10,000 joules of work into a car jack. The car jack, in turn, puts out 7000 joules of work to raise up the car. What is the efficiency of the jack? | text | null |
L_0733 | machines | T_3643 | Another measure of the effectiveness of a machine is its mechanical advantage. Mechanical advantage is the number of times a machine multiplies the input force. It can be calculated with the equation: Mechanical Advantage = Output force Input force This equation computes the actual mechanical advantage of a machine. It takes into account the reduction in output force that is due to friction. It shows how much a machine actually multiplies force when it used in the real world. | text | null |
L_0733 | machines | T_3644 | It can be difficult to measure the input and output forces needed to calculate actual mechanical advantage. Its usually much easier to measure the input and output distances. These measurements can then be used to calculate the ideal mechanical advantage. The ideal mechanical advantage represents the multiplication of input force that would be achieved in the absence of friction. Therefore, it is greater than the actual mechanical advantage because all machines use up some work in overcoming friction. Ideal mechanical advantage is calculated with the equation: Ideal Mechanical Advantage = Input distance Output distance Compare this equation with the equation above for actual mechanical advantage. Notice how the input and output values are switched. This makes sense when you recall that when a machine increases force, it decreases distance and vice versa. You can watch a video about actual and ideal mechanical advantage at this link: http://video.goo Consider the simple ramp in Figure 16.12. A ramp can be used to raise an object up off the ground. The input distance is the length of the sloped surface of the ramp. The output distance is the height of the ramp, or the vertical distance the object is raised. Therefore, the ideal mechanical advantage of the ramp is: Ideal Mechanical Advantage = 6m =3 2m An ideal mechanical advantage of 3 means that the ramp ideally (in the absence of friction) multiplies the output force by a factor of 3. | text | null |
L_0733 | machines | T_3645 | As you read above, some machines increase the force put into the machine, while other machines increase the distance over which the force is applied. Still other machines change only the direction of the force. Which way a machine works affects its mechanical advantage. For machines that increase force including ramps, doorknobs, and nutcrackers the output force is greater than the input force. Therefore, the mechanical advantage is greater than 1. For machines that increase the distance over which force is applied, such as paddles and hammers, the output force is less than the input force. Therefore, the mechanical advantage is less than 1. For machines that change only the direction of the force, such as the rope systems on flagpoles, the output force is the same as the input force. Therefore, the mechanical advantage is equal to 1. | text | null |
L_0734 | simple machines | T_3646 | The man in Figure 16.14 is using a ramp to move a heavy dryer up to the back of a truck. The highway in the figure switches back and forth so it climbs up the steep hillside. Both the ramp and the highway are examples of inclined planes. An inclined plane is a simple machine consisting of a sloping surface that connects lower and higher elevations. The sloping surface of the inclined plane supports part of the weight of the object as it moves up the slope. As a result, it takes less force to move the object uphill. The trade-off is that the object must be moved over a greater distance than if it were moved straight up to the higher elevation. On the other hand, the output force is greater than the input force because it is applied over a shorter distance. Like other simple machines, the ideal mechanical advantage of an inclined plane is given by: Ideal Mechanical Advantage = Input distance Output distance For an inclined plane, the input distance is the length of the sloping surface, and the output distance is the maximum height of the inclined plane. This was illustrated in Figure 16.12. Because the sloping surface is always greater than the height of the inclined plane, the ideal mechanical advantage of an inclined plane is always greater than 1. An inclined plane with a longer sloping surface relative to its height has a gentler slope. An inclined plane with a gentler slope has a greater mechanical advantage and requires less input force to move an object to a higher elevation. | text | null |
L_0734 | simple machines | T_3647 | Two simple machines that are based on the inclined plane are the wedge and the screw. Both increase the force used to move an object because the input force is applied over a greater distance than the output force. | text | null |
L_0734 | simple machines | T_3648 | Imagine trying to slice a tomato with a fork or spoon instead of a knife, like the one in Figure 16.15. The knife makes the job a lot easier because of the wedge shape of the blade. A wedge is a simple machine that consists of two inclined planes. But unlike one inclined plane, a wedge works only when it moves. It has a thin end and thick end, and the thin end is forced into an object to cut or split it. The chisel in Figure 16.15 is another example of a wedge. The input force is applied to the thick end of a wedge, and it acts over the length of the wedge. The output force pushes against the object on both sides of the wedge, so the output distance is the thickness of the wedge. Therefore, the ideal mechanical advantage of a wedge can be calculated as: Ideal Mechanical Advantage = Length of wedge Maximum thickness of wedge The length of a wedge is always greater than its maximum thickness. As a result, the ideal mechanical advantage of a wedge is always greater than 1. | text | null |
L_0734 | simple machines | T_3649 | The spiral staircase in Figure 16.16 also contains an inclined plane. Do you see it? The stairs that wrap around the inside of the walls make up the inclined plane. The spiral staircase is an example of a screw. A screw is a simple machine that consists of an inclined plane wrapped around a cylinder or cone. No doubt you are familiar with screws like the wood screw in Figure 16.16. The screw top of the container in the figure is another example. Screws move objects to a higher elevation (or greater depth) by increasing the force applied. When you use a wood screw, you apply force to turn the inclined plane. The output force pushes the screw into the wood. It acts along the length of the cylinder around which the inclined plane is wrapped. Therefore, the ideal mechanical advantage of a screw is calculated as: Ideal Mechanical Advantage = Length of inclined plane Length of screw The length of the inclined plane is always greater than the length of the screw. As a result, the mechanical advantage of a screw is always greater than 1. Look at the collection of screws and bolts in Figure 16.17. In some of them, the turns (or threads) of the inclined plane are closer together. The closer together the threads are, the longer the inclined plane is relative to the length of the screw or bolt, so the greater its mechanical advantage is. Therefore, if the threads are closer together, you need to apply less force to penetrate the wood or other object. The trade-off is that more turns of the screw or bolt are needed to do the job because the distance over which the input force must be applied is greater. | text | null |
L_0734 | simple machines | T_3649 | The spiral staircase in Figure 16.16 also contains an inclined plane. Do you see it? The stairs that wrap around the inside of the walls make up the inclined plane. The spiral staircase is an example of a screw. A screw is a simple machine that consists of an inclined plane wrapped around a cylinder or cone. No doubt you are familiar with screws like the wood screw in Figure 16.16. The screw top of the container in the figure is another example. Screws move objects to a higher elevation (or greater depth) by increasing the force applied. When you use a wood screw, you apply force to turn the inclined plane. The output force pushes the screw into the wood. It acts along the length of the cylinder around which the inclined plane is wrapped. Therefore, the ideal mechanical advantage of a screw is calculated as: Ideal Mechanical Advantage = Length of inclined plane Length of screw The length of the inclined plane is always greater than the length of the screw. As a result, the mechanical advantage of a screw is always greater than 1. Look at the collection of screws and bolts in Figure 16.17. In some of them, the turns (or threads) of the inclined plane are closer together. The closer together the threads are, the longer the inclined plane is relative to the length of the screw or bolt, so the greater its mechanical advantage is. Therefore, if the threads are closer together, you need to apply less force to penetrate the wood or other object. The trade-off is that more turns of the screw or bolt are needed to do the job because the distance over which the input force must be applied is greater. | text | null |
L_0734 | simple machines | T_3650 | Did you ever use a hammer to pull a nail out of a board? If not, you can see how its done in Figure 16.18. When you pull down on the handle of the hammer, the claw end pulls up on the nail. A hammer is an example of a lever. A lever is a simple machine consisting of a bar that rotates around a fixed point called the fulcrum. For a video introduction to levers using skateboards as examples, go to this link: MEDIA Click image to the left or use the URL below. URL: A lever may or may not increase the force applied, and it may or may not change the direction of the force. It all depends on the location of the input and output forces relative to the fulcrum. In this regard, there are three basic types of levers, called first-class, second-class, and third-class levers. Figure 16.19 describes the three classes. | text | null |
L_0734 | simple machines | T_3651 | All three classes of levers make work easier, but they do so in different ways. When the input and output forces are on opposite sides of the fulcrum, the lever changes the direction of the applied force. This occurs only with a first-class lever. When both the input and output forces are on the same side of the fulcrum, the direction of the applied force does not change. This occurs with both second- and third-class levers. When the input force is applied farther from the fulcrum, the input distance is greater than the output distance, so the ideal mechanical advantage is greater than 1. This always occurs with second-class levers and may occur with first-class levers. When the input force is applied closer to the fulcrum, the input distance is less than the output distance, so the ideal mechanical advantage is less than 1. This always occurs with third-class levers and may occur with first-class levers. When both forces are the same distance from the fulcrum, the input distance equals the output distance, so the ideal mechanical advantage equals 1. This occurs only with first class-levers. | text | null |
L_0734 | simple machines | T_3652 | You may be wondering why you would use a third-class lever when it doesnt change the direction or strength of the applied force. The advantage of a third-class lever is that the output force is applied over a greater distance than the input force. This means that the output end of the lever must move faster than the input end. Why would this be useful when you are moving a hockey stick or baseball bat, both of which are third-class levers? | text | null |
L_0734 | simple machines | T_3653 | Did you ever ride on a Ferris wheel, like the one pictured in Figure 16.20? If you did, then you know how thrilling the ride can be. A Ferris wheel is an example of a wheel and axle. A wheel and axle is a simple machine that consists of two connected rings or cylinders, one inside the other, which both turn in the same direction around a single center point. The smaller, inner ring or cylinder is called the axle. The bigger, outer ring or cylinder is called the wheel. The car steering wheel in Figure 16.20 is another example of a wheel and axle. In a wheel and axle, force may be applied either to the wheel or to the axle. In both cases, the direction of the force does not change, but the force is either increased or applied over a greater distance. When the input force is applied to the axle, as it is with a Ferris wheel, the wheel turns with less force, so the ideal mechanical advantage is less than 1. However, the wheel turns over a greater distance, so it turns faster than the axle. The speed of the wheel is one reason that the Ferris wheel ride is so exciting. When the input force is applied to the wheel, as it is with a steering wheel, the axle turns over a shorter distance but with greater force, so the ideal mechanical advantage is greater than 1. This allows you to turn the steering wheel with relatively little effort, while the axle of the steering wheel applies enough force to turn the car. | text | null |
L_0734 | simple machines | T_3654 | Another simple machine that uses a wheel is the pulley. A pulley is a simple machine that consists of a rope and grooved wheel. The rope fits into the groove in the wheel, and pulling on the rope turns the wheel. Figure 16.21 shows two common uses of pulleys. Some pulleys are attached to a beam or other secure surface and remain fixed in place. They are called fixed pulleys. Other pulleys are attached to the object being moved and are moveable themselves. They are called moveable pulleys. Sometimes, fixed and moveable pulleys are used together. They make up a compound pulley. The three types of pulleys are compared in Figure 16.22. In all three types, the ideal mechanical advantage is equal to the number of rope segments pulling up on the object. The more rope segments that are helping to do the lifting work, the less force that is needed for the job. You can experiment with an interactive animation of compound pulleys with various numbers of pulleys at this link: . In a single fixed pulley, only one rope segment lifts the object, so the ideal mechanical advantage is 1. This type of pulley doesnt increase the force, but it does change the direction of the force. This allows you to use your weight to pull on one end of the rope and more easily raise the object attached to the other end. In a single moveable pulley, two rope segments lift the object, so the ideal mechanical advantage is 2. This type of pulley doesnt change the direction of the force, but it does increase the force. In a compound pulley, two or more rope segments lift the object, so the ideal mechanical advantage is equal to or greater than 2. This type of pulley may or may not change the direction of the force, depending on the number and arrangement of pulleys. When several pulleys are combined, the increase in force may be very great. To learn more about the mechanical advantage of different types of pulleys, watch the video at this link: http://video | text | null |
L_0735 | compound machines | T_3655 | A compound machine is a machine that consists of more than one simple machine. Some compound machines consist of just two simple machines. For example, a wheelbarrow consists of a lever, as you read earlier in the lesson "Simple Machines," and also a wheel and axle. Other compound machines, such as cars, consist of hundreds or even thousands of simple machines. Two common examples of compound machines are scissors and fishing rods with reels. To view a young students compound machine invention that includes several simple machines, watch the video at this link: . To see if you can identify the simple machines in a lawn mower, go to the URL below and click on Find the Simple Machines. | text | null |
L_0735 | compound machines | T_3656 | Look at the scissors in Figure 16.24. As you can see from the figure, scissors consist of two levers and two wedges. You apply force to the handle ends of the levers, and the output force is exerted by the blade ends of the levers. The fulcrum of both levers is where they are joined together. Notice that the fulcrum lies between the input and output points, so the levers are first-class levers. They change the direction of force. They may or may not also increase force, depending on the relative lengths of the handles and blades. The blades themselves are wedges, with a sharp cutting edge and a thicker dull edge. | text | null |
L_0735 | compound machines | T_3657 | The fishing rod with reel shown in Figure 16.25 is another compound machine. The rod is a third-class lever, with the fulcrum on one end of the rod, the input force close to the fulcrum, and the output force at the other end of the rod. The output distance is greater than the input distance, so the angler can fling the fishing line far out into the water with just a flick of the wrist. The reel is a wheel and axle that works as a pulley. The fishing line is wrapped around the wheel. Using the handle to turn the axle of the wheel winds or unwinds the line. | text | null |
L_0735 | compound machines | T_3658 | Riding a bicycle might be easy. But the forces that allow humans to balance atop a bicycle are complex. QUEST visits Davis a city that loves its bicycles to take a ride on a research bicycle and explore a collection of antique bicycles. Scientists say studying the complicated physics of bicycling can lead to the design of safer, and more efficient bikes. For more information on the science of riding a bicycle, see MEDIA Click image to the left or use the URL below. URL: | text | null |
L_0735 | compound machines | T_3659 | Because compound machines have more moving parts than simple machines, they generally have more friction to overcome. As a result, compound machines tend to have lower efficiency than simple machines. When a compound machine consists of a large number of simple machines, friction may become a serious problem, and it may produce a lot of heat. Lubricants such as oil or grease may be used to coat the moving parts so they slide over each other more easily. This is how a cars friction is reduced. Compound machines have a greater mechanical advantage than simple machines. Thats because the mechanical advantage of a compound machine equals the product of the mechanical advantages of all its component simple machines. The greater the number of simple machines it contains, the greater is its mechanical advantage. | text | null |
L_0736 | types of energy | T_3660 | The concept of energy was first introduced in the chapter "States of Matter," where it is defined as the ability to cause change in matter. Energy can also be defined as the ability to do work. Work is done whenever a force is used to move matter. When work is done, energy is transferred from one object to another. For example, when the batter in Figure 17.2 uses energy to swing the bat, she transfers energy to the bat. The moving bat, in turn, transfers energy to the ball. Like work, energy is measured in the joule (J), or newtonmeter (Nm). Energy exists in different forms, which you can read about in the lesson "Forms of Energy" later in the chapter. Some forms of energy are mechanical, electrical, and chemical energy. Most forms of energy can also be classified as kinetic or potential energy. Kinetic and potential forms of mechanical energy are the focus of this lesson. Mechanical energy is the energy of objects that are moving or have the potential to move. | text | null |
L_0736 | types of energy | T_3661 | What do all the photos in Figure 17.3 have in common? All of them show things that are moving. Kinetic energy is the energy of moving matter. Anything that is moving has kinetic energy from the atoms in matter to the planets in solar systems. Things with kinetic energy can do work. For example, the hammer in the photo is doing the work of pounding the nail into the board. You can see a cartoon introduction to kinetic energy and its relation to work at this URL: . The amount of kinetic energy in a moving object depends on its mass and velocity. An object with greater mass or greater velocity has more kinetic energy. The kinetic energy of a moving object can be calculated with the equation: 1 Kinetic Energy (KE) = mass velocity2 2 This equation for kinetic energy shows that velocity affects kinetic energy more than mass does. For example, if mass doubles, kinetic energy also doubles. But if velocity doubles, kinetic energy increases by a factor of four. Thats because velocity is squared in the equation. You can see for yourself how mass and velocity affect kinetic energy by working through the problems below. Problem Solving Problem: Juan has a mass of 50 kg. If he is running at a velocity of 2 m/s, how much kinetic energy does he have? Solution: Use the formula: KE = 12 mass velocity2 1 50 kg (2 m/s2 ) 2 = 100 kg m2 /s2 = 100 N m, or 100 J KE = You Try It! Problem: What is Juans kinetic energy if he runs at a velocity of 4 m/s? Problem: Juans dad has a mass of 100 kg. How much kinetic energy does he have if he runs at a velocity of 2 m/s? | text | null |
L_0736 | types of energy | T_3662 | Did you ever see a scene like the one in Figure 17.4? In many parts of the world, trees lose their leaves in autumn. The leaves turn color and then fall from the trees to the ground. As the leaves are falling, they have kinetic energy. While they are still attached to the trees they also have energy, but its not because of motion. Instead, they have stored energy, called potential energy. An object has potential energy because of its position or shape. For example leaves on trees have potential energy because they could fall due to the pull of gravity. | text | null |
L_0736 | types of energy | T_3663 | Potential energy due to the position of an object above Earth is called gravitational potential energy. Like the leaves on trees, anything that is raised up above Earths surface has the potential to fall because of gravity. You can see examples of people with gravitational potential energy in Figure 17.5. 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 diver in Figure 17.5. If he weighs 70 newtons and the diving board is 5 meters above Earths surface, then his potential energy is: GPE = 70 N 5 m = 350 N m, or 350 J | text | null |
L_0736 | types of energy | T_3664 | Potential energy due to an objects shape is called elastic potential energy. This energy results when elastic objects are stretched or compressed. Their elasticity gives them the potential to return to their original shape. For example, the rubber band in Figure 17.6 has been stretched, but it will spring back to its original shape when released. Springs like the handspring in the figure have elastic potential energy when they are compressed. What will happen when the handspring is released? | text | null |
L_0736 | types of energy | T_3665 | Remember the diver in Figure 17.5? What happens when he jumps off the diving board? His gravitational potential energy changes to kinetic energy as he falls toward the water. However, he can regain his potential energy by getting out of the water and climbing back up to the diving board. This requires an input of kinetic energy. These changes in energy are examples of energy conversion, the process in which energy changes from one type or form to another. | text | null |
L_0736 | types of energy | T_3666 | The law of conservation of energy applies to energy conversions. Energy is not used up when it changes form, although some energy may be used to overcome friction, and this energy is usually given off as heat. For example, the divers kinetic energy at the bottom of his fall is the same as his potential energy when he was on the diving board, except for a small amount of heat resulting from friction with the air as he falls. | text | null |
L_0736 | types of energy | T_3667 | There are many other examples of energy conversions between potential and kinetic energy. Figure 17.7 describes how potential energy changes to kinetic energy and back again on swings and trampolines. You can see an animation of changes between potential and kinetic energy on a ramp at the URL below. Can you think of other examples? | text | null |
L_0736 | types of energy | T_3668 | QUEST teams up with Make Magazine to construct the latest must have, do-it-yourself device hacks and science projects. This week well show you how to make a tabletop linear accelerator that demonstrates the finer points of kinetic energy by shooting a steel ball. For more information on the tabletop linear accelerator, see http://science.k MEDIA Click image to the left or use the URL below. URL: | text | null |
L_0737 | forms of energy | T_3669 | Energy, or the ability to do work, can exist in many different forms. The photo in Figure 17.8 represents six of the eight different forms of energy that are described in this lesson. The guitarist gets the energy he needs to perform from chemical energy in food. He uses mechanical energy to pluck the strings of the guitar. The stage lights use electrical energy and give off both light energy and thermal energy, commonly called heat. The guitar also uses electrical energy, and it produces sound energy when the guitarist plucks the strings. For an introduction to all these forms of energy, go to this URL: . For an interactive animation about the different forms of energy, visit this URL: After you read below about different forms of energy, you can check your knowledge by doing the drag and drop quiz at this URL: . | text | null |
L_0737 | forms of energy | T_3670 | Mechanical energy is the energy of an object that is moving or has the potential to move. It is the sum of an objects kinetic and potential energy. In Figure 17.9, the basketball has mechanical energy because it is moving. The arrow in the same figure has mechanical energy because it has the potential to move due to the elasticity of the bow. What are some other examples of mechanical energy? | text | null |
L_0737 | forms of energy | T_3671 | Energy is stored in the bonds between atoms that make up compounds. This energy is called chemical energy, and it is a form of potential energy. If the bonds between atoms are broken, the energy is released and can do work. The wood in the fireplace in Figure 17.10 has chemical energy. The energy is released as thermal energy when the wood burns. People and many other living things meet their energy needs with chemical energy stored in food. When food molecules are broken down, the energy is released and may be used to do work. | text | null |
L_0737 | forms of energy | T_3672 | Electrons are negatively charged particles in atoms. Moving electrons have a form of kinetic energy called electrical energy. If youve ever experienced an electric outage, then you know how hard it is to get by without electrical energy. Most of the electrical energy we use is produced by power plants and arrives in our homes through wires. Two other sources of electrical energy are pictured in Figure 17.11. | text | null |
L_0737 | forms of energy | T_3673 | The nuclei of atoms are held together by powerful forces. This gives them a tremendous amount of stored energy, called nuclear energy. The energy can be released and used to do work. This happens in nuclear power plants when nuclei fission, or split apart. It also happens in the sun and other stars when nuclei fuse, or join together. Some of the suns energy travels to Earth, where it warms the planet and provides the energy for photosynthesis (see Figure | text | null |
L_0737 | forms of energy | T_3674 | The atoms that make up matter are in constant motion, so they have kinetic energy. All that motion gives matter thermal energy. Thermal energy is defined as the total kinetic energy of all the atoms that make up an object. It depends on how fast the atoms are moving and how many atoms the object has. Therefore, an object with more mass has greater thermal energy than an object with less mass, even if their individual atoms are moving at the same speed. You can see an example of this in Figure 17.13. | text | null |
L_0737 | forms of energy | T_3674 | The atoms that make up matter are in constant motion, so they have kinetic energy. All that motion gives matter thermal energy. Thermal energy is defined as the total kinetic energy of all the atoms that make up an object. It depends on how fast the atoms are moving and how many atoms the object has. Therefore, an object with more mass has greater thermal energy than an object with less mass, even if their individual atoms are moving at the same speed. You can see an example of this in Figure 17.13. | text | null |
L_0737 | forms of energy | T_3675 | Energy that the sun and other stars release into space is called electromagnetic energy. This form of energy travels through space as electrical and magnetic waves. Electromagnetic energy is commonly called light. It includes visible light, as well as radio waves, microwaves, and X rays (Figure 17.14). | text | null |
L_0737 | forms of energy | T_3676 | The drummer in Figure 17.15 is hitting the drumheads with drumsticks. This causes the drumheads to vibrate. The vibrations pass to surrounding air particles and then from one air particle to another in a wave of energy called sound energy. We hear sound when the sound waves reach our ears. Sound energy can travel through air, water, and other substances, but not through empty space. Thats because the energy needs particles of matter to pass it on. | text | null |
L_0737 | forms of energy | T_3677 | Energy often changes from one form to another. For example, the mechanical energy of a moving drumstick changes to sound energy when it strikes the drumhead and causes it to vibrate. Any form of energy can change into any other form. Frequently, one form of energy changes into two or more different forms. For example, when wood burns, the woods chemical energy changes to both thermal energy and light energy. Other examples of energy conversions are described in Figure 17.16. You can see still others at this URL: http://fi.edu/guide/hughes/energychangeex.html . You can check your understanding of how energy changes form by doing the quizzes at these URLs: Energy is conserved in energy conversions. No energy is lost when energy changes form, although some may be released as thermal energy due to friction. For example, not all of the energy put into a steam turbine in Figure 17.16 changes to electrical energy. Some changes to thermal energy because of friction of the turning blades and other moving parts. The more efficient a device is, the greater the percentage of usable energy it produces. Appliances with an "Energy Star" label like the one in Figure 17.17 use energy efficiently and thereby reduce energy use. | text | null |
L_0738 | energy resources | T_3678 | Nonrenewable resources are natural resources that are limited in supply and cannot be replaced except over millions of years. Nonrenewable energy resources include fossil fuels and radioactive elements such as uranium. | text | null |
L_0738 | energy resources | T_3679 | Fossil fuels are mixtures of hydrocarbons that formed over millions of years from the remains of dead organisms. They include petroleum (commonly called oil), natural gas, and coal. Fossil fuels provide most of the energy used in the world today. They are burned in power plants to produce electrical energy, and they also fuel cars, heat homes, and supply energy for many other purposes. You can see examples of their use in Figure 17.19. Fossil fuels contain stored chemical energy that came originally from the sun. Ancient plants changed energy in | text | null |
L_0738 | energy resources | T_3679 | Fossil fuels are mixtures of hydrocarbons that formed over millions of years from the remains of dead organisms. They include petroleum (commonly called oil), natural gas, and coal. Fossil fuels provide most of the energy used in the world today. They are burned in power plants to produce electrical energy, and they also fuel cars, heat homes, and supply energy for many other purposes. You can see examples of their use in Figure 17.19. Fossil fuels contain stored chemical energy that came originally from the sun. Ancient plants changed energy in | text | null |
L_0738 | energy resources | T_3680 | Like fossil fuels, the radioactive element uranium can be used to generate electrical energy in power plants. In a nuclear power plant, the nuclei of uranium atoms are split in the process of nuclear fission. This process releases a tremendous amount of energy from just a small amount of uranium. The total supply of uranium in the world is quite limited, however, and cannot be replaced once it is used up. This makes nuclear energy a nonrenewable resource. Although using nuclear energy does not release carbon dioxide or cause air pollution, it does produce dangerous radioactive wastes. Accidents at nuclear power plants also have the potential to release large amounts of radioactive material into the environment. Figure 17.21 describes the nuclear disaster caused by a Japanese tsunami in 2011. You can learn more about the disaster and its aftermath at the URLs below. | text | null |
L_0738 | energy resources | T_3681 | President Obama says the United States needs new nuclear reactors, to meet the countrys energy demands and counter climate change. But can nuclear power be produced more safely and affordably? A scientist at the University of California, Berkeley, is working to do just that. For more information about nuclear energy, see http://science.k MEDIA Click image to the left or use the URL below. URL: | text | null |
L_0738 | energy resources | T_3682 | Renewable resources are natural resources that can be replaced in a relatively short period of time or are virtually limitless in supply. Renewable energy resources include sunlight, moving water, wind, biomass, and geothermal energy. Each of these energy resources is described in Table 17.1. Resources such as sunlight and wind are limitless in supply, so they will never run out. Besides their availability, renewable energy resources also have the advantage of producing little if any pollution and not contributing to global warming. The technology needed to gather energy from renewable resources is currently expensive to install, but most of the resources themselves are free for the taking. here? Renewable Energy Resource Sunlight The energy in sunlight, or solar energy, can be used to heat homes. It can also be used to produce electricity in solar cells. However, solar energy may not be practical in areas that are often cloudy. Example Solar panels on the roof of this house generate enough electricity to supply a familys needs. Moving Water When water falls downhill, its potential energy is con- verted to kinetic energy that can turn a turbine and generate electricity. The water may fall naturally over a waterfall or flow through a dam. A drawback of dams is that they flood land upstream and reduce water flow downstream. Either effect may harm ecosystems. Wind Wind is moving air, so it has kinetic energy that can do work. Remember the wind turbines that opened this chapter? Wind turbines change the kinetic energy of the wind to electrical energy. Only certain areas of the world get enough steady wind to produce much electricity. Many people also think that wind turbines are noisy and unattractive in the landscape. Water flowing through Hoover dam between Arizona and Nevada generates electricity for both of these states and also by southern California. The dam spans the Colorado River. This old-fashioned windmill captures wind energy that is used for pumping water out of a well. Windmills like this one have been used for centuries. Renewable Energy Resource Biomass The stored chemical energy of trees and other plants is called biomass energy. When plant materials are burned, they produce thermal energy that can be used for heating, cooking, or generating electricity. Biomassespecially woodis an important energy source in countries where most people cant afford fossil fuels. Some plants can also be used to make ethanol, a fuel that is added to gasoline. Ethanol produces less pollution than gasoline, but large areas of land are needed to grow the plants needed to make it. Geothermal Heat below Earths surfacecalled geothermal en- ergycan be used to produce electricity. A power plant pumps water underground where it is heated. Then it pumps the water back to the plant and uses its thermal energy to generate electricity. On a small scale, geothermal energy can be used to heat homes. Installing a geothermal system can be very costly, how- ever, because of the need to drill through underground rocks. Example This large machine is harvesting and grinding plants to be used for biomass energy. This geothermal power plant is located in Italy where hot magma is close to the surface. | text | null |
L_0738 | energy resources | T_3683 | The largest solar thermal plant in the world opens in Californias Mojave Desert, after a debate that pitted renewable energy against a threatened tortoise. The Ivanpah solar plant is one of seven big solar farms scheduled to open in California in the coming months, as a result of the states push to produce one third of its electricity from renewable energy. Some 30 states have similar mandates. For more information on this solar plant, see http://science.kqed.org/ MEDIA Click image to the left or use the URL below. URL: | text | null |
L_0738 | energy resources | T_3684 | On the windswept tarmac of the former Alameda Naval Air Station, an inventive group of scientists and engineers are test-flying a kite-like tethered wing that may someday help revolutionize clean energy. QUEST explores the potential of wind energy and new airborne wind turbines designed to harness the stronger and more consistent winds found at higher altitudes. For more information on wind energy, see http://science.kqed.org/quest/video/airborne MEDIA Click image to the left or use the URL below. URL: | text | null |
L_0738 | energy resources | T_3685 | Solar and wind power may get the headlines when it comes to renewable energy. But another type of clean power is heating up in the hills just north of Sonoma wine country. Geothermal power uses heat from deep inside the Earth to generate electricity. The Geysers, the worlds largest power-producing geothermal field, has been providing electricity for roughly 850,000 Northern California households, and is set to expand even further. For more information on geothermal energy, see http://science.kqed.org/quest/video/geothermal-heats-up/ . MEDIA Click image to the left or use the URL below. URL: | text | null |
L_0738 | energy resources | T_3686 | Figure 17.22 shows the mix of energy resources used worldwide in 2006. Fossil fuels still provide most of the worlds energy, with oil being the single most commonly used energy resource. Natural gas is used less than the other two fossil fuels, but even natural gas is used more than all renewable energy resources combined. Wind, solar, and geothermal energy contribute the least to global energy use, despite the fact that they are virtually limitless in supply and nonpolluting. | text | null |
L_0738 | energy resources | T_3687 | People in the richer nations of the world use far more energy, especially energy from fossil fuels, than people in the poorer nations do. Figure 17.23 compares the amounts of oil used by the top ten oil-consuming nations. The U.S. uses more oil than several other top-ten countries combined. If you also consider the population size in these countries, the differences are even more stunning. The average person in the U.S. uses a whopping 23 barrels of oil a year! In comparison, the average person in India or China uses just 1 or 2 barrels a year. Because richer nations use more fossil fuels, they also cause more air pollution and global warming than poorer nations do. | text | null |
L_0738 | energy resources | T_3688 | We can reduce our use of energy resources and the pollution they cause by conserving energy. Conservation means saving resources by using them more efficiently or not using them at all. Figure 17.24 shows several ways that people can conserve energy in their daily lives. You can find more energy-saving tips at the URL below. What do you do to save energy? What else could you do? | text | null |
L_0738 | energy resources | T_3688 | We can reduce our use of energy resources and the pollution they cause by conserving energy. Conservation means saving resources by using them more efficiently or not using them at all. Figure 17.24 shows several ways that people can conserve energy in their daily lives. You can find more energy-saving tips at the URL below. What do you do to save energy? What else could you do? | text | null |
L_0738 | energy resources | T_3688 | We can reduce our use of energy resources and the pollution they cause by conserving energy. Conservation means saving resources by using them more efficiently or not using them at all. Figure 17.24 shows several ways that people can conserve energy in their daily lives. You can find more energy-saving tips at the URL below. What do you do to save energy? What else could you do? | text | null |
L_0738 | energy resources | T_3689 | QUEST teams up with Climate Watch to give you an inside look at home energy efficiency. Tag along with Sustainable Spaces on a home efficiency "green-up" and learn tips on how to make your home more energy efficient. For more information on home energy audits, see http://science.kqed.org/quest/video/web-extra-home-energy-audit/ . MEDIA Click image to the left or use the URL below. URL: | text | null |
L_0738 | energy resources | T_3690 | With the race on to reduce global warming and fossil fuel dependency, experts in alternative energy see a bright future for renewable resources like wind, solar, hydro-power and geothermal energy. QUEST and Climate Watch team up to look at the "Smart Grid" of the future and how it might be improved to more cleanly and efficiently keep the lights on in California. For more information on the "Smart Grid", see http://science.kqed.org/quest/video/clim MEDIA Click image to the left or use the URL below. URL: | text | null |
L_0739 | temperature and heat | T_3691 | No doubt you already have a good idea of what temperature is. You might define it as how hot or cold something feels. In physics, temperature is defined as the average kinetic energy of the particles in an object. When particles move more quickly, temperature is higher and an object feels warmer. When particles move more slowly, temperature is lower and an object feels cooler. | text | null |
L_0739 | temperature and heat | T_3692 | If two objects have the same mass, the object with the higher temperature has greater thermal energy. Temperature affects thermal energy, but temperature isnt the same thing as thermal energy. Thats because an objects mass also affects its thermal energy. The examples in Figure 18.1 make this clear. In the figure, the particles of cocoa are moving faster than the particles of bathwater. Therefore, the cocoa has a higher temperature. However, the bath water has more thermal energy because there is so much more of it. It has many more moving particles. Bill Nye the Science Guy cleverly discusses these concepts at this URL: MEDIA Click image to the left or use the URL below. URL: If youre still not clear about the relationship between temperature and thermal energy, watch the animation "Tem- perature" at this URL: . | text | null |
L_0739 | temperature and heat | T_3693 | Temperature is measured with a thermometer. A thermometer shows how hot or cold something is relative to two reference temperatures, usually the freezing and boiling points of water. Scientists often use the Celsius scale for temperature. On this scale, the freezing point of water is 0C and the boiling point is 100C. To learn more about measuring temperature, watch the animation Measuring Temperature at this URL: Did you ever wonder how a thermometer works? Look at the thermometer in Figure 18.2. Particles of the red liquid have greater energy when they are warmer, so they move more and spread apart. This causes the liquid to expand and rise higher in the glass tube. Like the liquid in a thermometer, most types of matter expand to some degree when they get warmer. Gases usually expand the most when heated, followed by liquids. Solids generally expand the least. (Water is an exception; it takes up more space as a solid than as a liquid.) | text | null |
L_0739 | temperature and heat | T_3694 | Something that has a high temperature is said to be hot. Does temperature measure heat? Is heat just another word for thermal energy? The answer to both questions is no. Heat is the transfer of thermal energy between objects that have different temperatures. Thermal energy always moves from an object with a higher temperature to an object with a lower temperature. When thermal energy is transferred in this way, the warm object becomes cooler and the cool object becomes warmer. Sooner or later, both objects will have the same temperature. Only then does the transfer of thermal energy end. For a visual explanation of these concepts, watch the animation "Temperature vs. Heat" at this URL: . | text | null |
L_0739 | temperature and heat | T_3695 | Figure 18.3 illustrates an example of thermal energy transfer. Before the spoon was put into the steaming hot coffee, it was cool to the touch. Once in the coffee, the spoon heated up quickly. The fast-moving particles of the coffee transferred some of their energy to the slower-moving particles of the spoon. The spoon particles started moving faster and became warmer, causing the temperature of the spoon to rise. Because the coffee particles lost some of their kinetic energy to the spoon particles, the coffee particles started to move more slowly. This caused the temperature of the coffee to fall. Before long, the coffee and spoon had the same temperature. | text | null |
L_0739 | temperature and heat | T_3696 | The girls in Figure 18.4 are having fun at the beach. Its a warm, sunny day, and the sand feels hot under their bare hands and feet. The water, in contrast, feels much cooler. Why does the sand get so hot while the water does not? The answer has to do with specific heat. Specific heat is the amount of energy (in joules) needed to raise the temperature of 1 gram of a substance by 1C. Specific heat is a property that is specific to a given type of matter. Table 18.1 lists the specific heat of four different substances. Metals such as iron have relatively low specific heat. It doesnt take much energy to raise their temperature. Thats why a metal spoon heats up quickly when placed in hot coffee. Sand also has a relatively low specific heat, whereas water has a very high specific heat. It takes a lot more energy to increase the temperature of water than sand. This explains why the sand on a beach gets hot while the water stays cool. Differences in the specific heat of water and land also affect climate. To learn how, watch the video at this URL: MEDIA Click image to the left or use the URL below. URL: In Table 18.1, how much greater is the specific heat of water than sand? Substances iron sand wood water Specific Heat (joules) 0.45 0.67 1.76 4.18 | text | null |
L_0739 | temperature and heat | T_3697 | The roadway across the Golden Gate Bridge rises and falls as much as 16 feet depending on the temperature. When the sun hits the bridge, the metal expands and the bridge cables stretch. As the fog rolls in, the cables contract and the bridge goes up. Curators from the Outdoor Exploratorium in San Francisco have set up a scope two miles away so you can see how the bridge is moving up or down depending on the weather. For more information on how the bridge moves due to temperature, see http://science.kqed.org/quest/video/quest-lab-bridge-thermometer/ . Heat is the transfer of thermal energy between objects that have different temperatures. Thermal energy always moves from an object with a higher temperature to an object with a lower temperature. Specific heat is the amount of energy (in joules) needed to raise the temperature of 1 gram of a substance by 1C. Substances differ in their specific heat. | text | null |
L_0740 | transfer of thermal energy | T_3698 | Conduction is the transfer of thermal energy between particles of matter that are touching. When energetic particles collide with nearby particles, they transfer some of their thermal energy. From particle to particle, like dominoes falling, thermal energy moves throughout a substance. In Figure 18.5, conduction occurs between particles of the metal in the pot and between particles of the pot and the water. Figure 18.6 shows additional examples of conduction. For a deeper understanding of this method of heat transfer, watch the animation "Conduction" at this URL: http://w | text | null |
L_0740 | transfer of thermal energy | T_3699 | Conduction is usually faster in liquids and certain solids than in gases. Materials that are good conductors of thermal energy are called thermal conductors. Metals are excellent thermal conductors. They have freely moving electrons that can transfer energy quickly and easily. Thats why the metal pot in Figure 18.5 soon gets hot all over, even though it gains thermal energy from the fire only at the bottom of the pot. In Figure 18.6, the metal heating element of the curling iron heats up almost instantly and quickly transfers energy to the strands of hair that it touches. | text | null |
L_0740 | transfer of thermal energy | T_3700 | Particles of gases are farther apart and have fewer collisions, so they are not good at transferring thermal energy. Materials that are poor thermal conductors are called thermal insulators. Figure 18.7 shows several examples. Fluffy yellow insulation inside the roof of a home is full of air. The air prevents the transfer of thermal energy into the house on hot days and out of the house on cold days. A puffy down jacket keeps you warm in the winter for the same reason. Its feather filling holds trapped air that prevents energy transfer from your warm body to the cold air outside. Solids like plastic and wood are also good thermal insulators. Thats why pot handles and cooking utensils are often made of these materials. | text | null |
L_0740 | transfer of thermal energy | T_3701 | Everyday, women living in the refugee camps of Darfur, Sudan must walk for up to seven hours outside the safety of the camps to collect firewood for cooking, putting them at risk for violent attacks. Now, researchers at Lawrence Berkeley National Laboratory have engineered a more efficient wood-burning stove, which is greatly reducing both the womens need for firewood and the threats against them. For more information on these stoves, see http://scien MEDIA Click image to the left or use the URL below. URL: | text | null |
L_0740 | transfer of thermal energy | T_3702 | Convection is the transfer of thermal energy by particles moving through a fluid. Particles transfer energy by moving from warmer to cooler areas. Thats how energy is transferred in the soup in Figure 18.7. Particles of soup near the bottom of the pot get hot first. They have more energy so they spread out and become less dense. With lower density, these particles rise to the top of the pot (see Figure 18.8). By the time they reach the top of the pot they have cooled off. They have less energy to move apart, so they become denser. With greater density, the particles sink to the bottom of the pot, and the cycle repeats. This loop of moving particles is called a convection current. Convection currents move thermal energy through many fluids, including molten rock inside Earth, water in the oceans, and air in the atmosphere. In the atmosphere, convection currents create wind. You can see one way this happens in Figure 18.9. Land heats up and cools off faster than water because it has lower specific heat. Therefore, land is warmer during the day and cooler at night than water. Air close to the surface gains or loses heat as well. Warm air rises because it is less dense, and when it does, cool air moves in to take its place. This creates a convection current that carries air from the warmer to the cooler area. You can learn more about convection currents by watching "Convection" at this URL: . | text | null |
L_0740 | transfer of thermal energy | T_3702 | Convection is the transfer of thermal energy by particles moving through a fluid. Particles transfer energy by moving from warmer to cooler areas. Thats how energy is transferred in the soup in Figure 18.7. Particles of soup near the bottom of the pot get hot first. They have more energy so they spread out and become less dense. With lower density, these particles rise to the top of the pot (see Figure 18.8). By the time they reach the top of the pot they have cooled off. They have less energy to move apart, so they become denser. With greater density, the particles sink to the bottom of the pot, and the cycle repeats. This loop of moving particles is called a convection current. Convection currents move thermal energy through many fluids, including molten rock inside Earth, water in the oceans, and air in the atmosphere. In the atmosphere, convection currents create wind. You can see one way this happens in Figure 18.9. Land heats up and cools off faster than water because it has lower specific heat. Therefore, land is warmer during the day and cooler at night than water. Air close to the surface gains or loses heat as well. Warm air rises because it is less dense, and when it does, cool air moves in to take its place. This creates a convection current that carries air from the warmer to the cooler area. You can learn more about convection currents by watching "Convection" at this URL: . | text | null |
L_0740 | transfer of thermal energy | T_3703 | Both conduction and convection transfer energy through matter. Radiation is the only way of transferring energy that doesnt require matter. Radiation is the transfer of energy by waves that can travel through empty space. When the waves reach objects, they transfer energy to the objects, causing them to warm up. This is how the suns energy reaches Earth and heats its surface (see Figure 18.10). Radiation is also how thermal energy from a campfire warms people nearby. You might be surprised to learn that all objects radiate thermal energy, including people. In fact, when a room is full of people, it may feel noticeably warmer because of all the thermal energy the people radiate! To learn more about thermal radiation, watch "Radiation" at the URL below. | text | null |
L_0741 | using thermal energy | T_3704 | Warming homes and other buildings is an obvious way that thermal energy can be used. Two common types of home heating systems are hot-water and warm-air heating systems. Both types are described below. You can watch an animation showing how a solar heating system works at this URL: | text | null |
L_0741 | using thermal energy | T_3705 | A hot-water heating system uses thermal energy to heat water and then pumps the hot water throughout the building in a system of pipes and radiators. You can see a diagram of this type of heating system in Figure 18.12. Typically, the water is heated in a boiler that burns natural gas or heating oil. There is usually a radiator in each room that gets warm when the hot water flows through it. The radiator transfers thermal energy to the air around it by conduction and radiation. The warm air then circulates throughout the room in convection currents. The hot water cools as it flows through the system and transfers its thermal energy. When it finally returns to the boiler, it is heated again and the cycle repeats. | text | null |
L_0741 | using thermal energy | T_3706 | A warm-air heating system uses thermal energy to heat air. It then forces the warm air through a system of ducts. You can see a diagram of this type of heating system in Figure 18.13. Typically, the air is heated in a furnace that burns natural gas or heating oil. When the air is warm, a fan blows it through the ducts and out through vents that are located in each room. Warm air blowing out of a vent moves across the room, pushing cold air out of the way. The cold air enters an intake vent on the opposite side of the room and returns to the furnace with the help of another fan. In the furnace, the cold air is heated, and the cycle repeats. | text | null |
L_0741 | using thermal energy | T_3707 | Its easy to see how thermal energy can be used to keep things warm. But did you know that thermal energy can also be used to keep things cool? Cooling systems such as air conditioners and refrigerators transfer thermal energy in order to keep homes and cars cool or to keep food cold. In a refrigerator, for example, thermal energy is transferred from the cool air inside the refrigerator to the warmer air in the kitchen. You read in this chapters "Transfer of Thermal Energy" lesson that thermal energy always moves from a warmer area to a cooler area, so how can it move from the cooler refrigerator to the warmer room? The answer is work. The refrigerator does work to transfer thermal energy in this way. Doing this work takes energy, which is usually provided by electricity. Figure 18.14 explains how a refrigerator does its work. For an animated demonstration of how a refrigerator works, go to this URL: The key to how a refrigerator or other cooling system works is the refrigerant. A refrigerant is a substance, such as FreonTM, that has a low boiling point and changes between liquid and gaseous states as it passes through the cooling system. As a liquid, the refrigerant absorbs thermal energy from the cool air inside the refrigerator and changes to a gas. As a gas, it releases thermal energy to the warm air outside the refrigerator and changes back to a liquid. | text | null |
L_0741 | using thermal energy | T_3708 | A combustion engine is a complex machine that burns fuel to produce thermal energy and then uses the energy to do work. Two basic types of combustion engines are external and internal combustion engines. | text | null |
L_0741 | using thermal energy | T_3709 | An external combustion engine burns fuel externally, or outside the engine. The burning fuel releases thermal energy that is used to turn water to steam. The pressure of the steam is then used to move a piston back and forth in a cylinder. The kinetic energy of the moving piston can be used to turn a turbine or other device. Figure 18.15 explains in greater detail how this type of engine works. You can see an animated version of an external combustion engine at this URL: http://science.howstuffworks.com/transport/engines-equipment/steam1.htm . | text | null |
L_0741 | using thermal energy | T_3710 | An internal combustion engine (see Figure 18.16) burns fuel internally, or inside the engine. This type of engine is found in most cars and other motor vehicles. It works in these steps, which keep repeating: 1. A mixture of fuel and air is pulled into a cylinder through a valve, which then closes. 2. The piston is pushed upward, compressing the fuel-air mixture in the closed cylinder. The mixture is now under a lot of pressure and very warm. 3. A spark from a spark plug is used to ignite the fuel-air mixture, causing it to burn explosively within the confined space of the closed cylinder. 4. The pressure of the hot gases from combustion forces the piston downward. 5. When the piston moves up again, it forces the exhaust gases of combustion out of the cylinder though another valve. Then the process repeats. In a car, the piston is connected by the piston rod to the crankshaft. The crankshaft rotates when the piston moves up and down. The kinetic energy of the moving crankshaft is used to turn the driveshaft, which causes the wheels of the car to turn. Most cars have at least four cylinders connected to the crankshaft. Their pistons move up and down in sequence, one after the other. You can watch animations of internal combustion engines in action at these URLs: http://auto.howstuffworks.com/engine1.htm | text | null |
L_0742 | characteristics of waves | T_3711 | A mechanical wave is a disturbance in matter that transfers energy from place to place. A mechanical wave starts when matter is disturbed. An example of a mechanical wave is pictured in Figure 19.1. A drop of water falls into a pond. This disturbs the water in the pond. What happens next? The disturbance travels outward from the drop in all directions. This is the wave. A source of energy is needed to start a mechanical wave. In this case, the energy comes from the falling drop of water. | text | null |
L_0742 | characteristics of waves | T_3712 | The energy of a mechanical wave can travel only through matter. This matter is called the medium (plural, media). The medium in Figure 19.1 is a liquid the water in the pond. But the medium of a mechanical wave can be any state of matter, including a solid or a gas. Its important to note that particles of matter in the medium dont actually travel along with the wave. Only the energy travels. The particles of the medium just vibrate, or move back-and- forth or up-and-down in one spot, always returning to their original positions. As the particles vibrate, they pass the energy of the disturbance to the particles next to them, which pass the energy to the particles next to them, and so on. | text | null |
L_0742 | characteristics of waves | T_3713 | There are three types of mechanical waves. They differ in how they travel through a medium. The three types are transverse, longitudinal, and surface waves. All three types are described in detail below. | text | null |
L_0742 | characteristics of waves | T_3714 | A transverse wave is a wave in which the medium vibrates at right angles to the direction that the wave travels. An example of a transverse wave is a wave in a rope, like the one pictured in Figure 19.2. In this wave, energy is provided by a persons hand moving one end of the rope up and down. The direction of the wave is down the length of the rope away from the persons hand. The rope itself moves up and down as the wave passes through it. You can see a brief video of a transverse wave in a rope at this URL: . To see a transverse wave in slow motion, go to this URL: (0:22). MEDIA Click image to the left or use the URL below. URL: | text | null |
L_0742 | characteristics of waves | T_3715 | A transverse wave can be characterized by the high and low points reached by particles of the medium as the wave passes through. This is illustrated in Figure 19.3. The high points are called crests, and the low points are called troughs. | text | null |
L_0742 | characteristics of waves | T_3716 | Another example of transverse waves occurs with earthquakes. The disturbance that causes an earthquake sends transverse waves through underground rocks in all directions from the disturbance. Earthquake waves that travel this way are called secondary, or S, waves. An S wave is illustrated in Figure 19.4. | text | null |
L_0742 | characteristics of waves | T_3716 | Another example of transverse waves occurs with earthquakes. The disturbance that causes an earthquake sends transverse waves through underground rocks in all directions from the disturbance. Earthquake waves that travel this way are called secondary, or S, waves. An S wave is illustrated in Figure 19.4. | text | null |
L_0742 | characteristics of waves | T_3716 | Another example of transverse waves occurs with earthquakes. The disturbance that causes an earthquake sends transverse waves through underground rocks in all directions from the disturbance. Earthquake waves that travel this way are called secondary, or S, waves. An S wave is illustrated in Figure 19.4. | text | null |
L_0742 | characteristics of waves | T_3717 | A longitudinal wave is a wave in which the medium vibrates in the same direction that the wave travels. An example of a longitudinal wave is a wave in a spring, like the one in Figure 19.5. In this wave, the energy is provided by a persons hand pushing and pulling the spring. The coils of the spring first crowd closer together and then spread farther apart as the disturbance passes through them. The direction of the wave is down the length of the spring, or the same direction in which the coils move. You can see a video of a longitudinal wave in a spring at this URL: http | text | null |
L_0742 | characteristics of waves | T_3718 | A longitudinal wave can be characterized by the compressions and rarefactions of the medium. This is illustrated in Figure 19.6. Compressions are the places where the coils are crowded together, and rarefactions are the places where the coils are spread apart. | text | null |
L_0742 | characteristics of waves | T_3719 | Earthquakes cause longitudinal waves as well as transverse waves. The disturbance that causes an earthquake sends longitudinal waves through underground rocks in all directions from the disturbance. Earthquake waves that travel this way are called primary, or P, waves. They are illustrated in Figure 19.7. | text | null |
L_0742 | characteristics of waves | T_3719 | Earthquakes cause longitudinal waves as well as transverse waves. The disturbance that causes an earthquake sends longitudinal waves through underground rocks in all directions from the disturbance. Earthquake waves that travel this way are called primary, or P, waves. They are illustrated in Figure 19.7. | text | null |
L_0742 | characteristics of waves | T_3720 | A surface wave is a wave that travels along the surface of a medium. It combines a transverse wave and a longitudinal wave. Ocean waves are surface waves. They travel on the surface of the water between the ocean and the air. In a surface wave, particles of the medium move up and down as well as back and forth. This gives them an overall circular motion. This is illustrated in Figure 19.8 and at the URL below. MEDIA Click image to the left or use the URL below. URL: In deep water, particles of water just move in circles. They dont actually move closer to shore with the energy of the waves. However, near the shore where the water is shallow, the waves behave differently. They start to drag on the bottom, creating friction (see Figure 19.9). The friction slows down the bottoms of the waves, while the tops of the waves keep moving at the same speed. This causes the waves to get steeper until they topple over and crash on the shore. The crashing waves carry water onto the shore as surf. | text | null |
L_0743 | measuring waves | T_3721 | The height of a wave is its amplitude. Another measure of wave size is wavelength. Both wave amplitude and wave- length are described in detail below. Figure 19.11 shows these wave measures for both transverse and longitudinal waves. You can also simulate waves with different amplitudes and wavelengths by doing the interactive animation at this URL: http://sci-culture.com/advancedpoll/GCSE/sine%20wave%20simulator.html . | text | null |
L_0743 | measuring waves | T_3722 | Wave amplitude is the maximum distance the particles of a medium move from their resting position when a wave passes through. The resting position is where the particles would be in the absence of a wave. In a transverse wave, wave amplitude is the height of each crest above the resting position. The higher the crests are, the greater the amplitude. In a longitudinal wave, amplitude is a measure of how compressed particles of the medium become when the wave passes through. The closer together the particles are, the greater the amplitude. What determines a waves amplitude? It depends on the energy of the disturbance that causes the wave. 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, like those in Figure 19.1. The ripples are low-amplitude waves. Now imagine throwing a big boulder into the pond. Very large waves will be generated by the disturbance. These waves are high-amplitude waves. | text | null |
L_0743 | measuring waves | T_3723 | Another important measure of wave size is wavelength. Wavelength is the distance between two corresponding points on adjacent waves (see Figure 19.11). Wavelength can be measured as the distance between two adjacent crests of a transverse wave or two adjacent compressions of a longitudinal wave. It is usually measured in meters. Wavelength is related to the energy of a wave. Short-wavelength waves have more energy than long-wavelength waves of the same amplitude. You can see examples of waves with shorter and longer wavelengths in Figure 19.12. | text | null |
L_0743 | measuring waves | T_3724 | Imagine making transverse waves in a rope, like the waves in Figure 19.2. You tie one end of the rope to a doorknob or other fixed point and move the other end up and down with your hand. You can move the rope up and down slowly or quickly. How quickly you move the rope determines the frequency of the waves. | text | null |
L_0743 | measuring waves | T_3725 | 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 or compressions that pass the point in 1 second or other time period. The higher the number is, the greater is the frequency of the wave. The SI unit for wave frequency is the hertz (Hz), where 1 hertz equals 1 wave passing a fixed point in 1 second. Figure 19.13 shows high-frequency and low- frequency transverse waves. You can simulate transverse waves with different frequencies at this URL: http://zonal 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. | text | null |
L_0743 | measuring waves | T_3726 | Assume that you move one end of a rope up and down just once. How long will take the wave to travel down the rope to the other end? This depends on the speed of the wave. Wave speed is how far the wave travels in a given amount of time, such as how many meters it travels per second. Wave speed is not the same thing as wave frequency, but it is related to frequency and also to wavelength. This equation shows how the three factors are related: Speed = Wavelength Frequency In this equation, wavelength is measured in meters and frequency is measured in hertz, or number of waves per second. Therefore, wave speed is given in meters per second. 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 1 wave/s = 3 m/s You Try It! Problem: Jera made a wave in a spring by pushing and pulling on one end. The wavelength is 0.1 m, and the wave frequency is 0.2 m/s. What is the speed of the wave? If you want more practice calculating wave speed from wavelength and frequency, try the problems at this URL: http The equation for wave speed (above) can be rewritten as: Frequency = Speed Speed or Wavelength = Wavelength 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 = 2 m/s = 2 waves/s, or 2 Hz 1m You Try It! Problem: A wave is traveling at a speed of 2 m/s and has a frequency of 2 Hz. What is its wavelength? | text | null |
L_0743 | measuring waves | T_3727 | The speed of most waves depends on the medium through which they are traveling. Generally, waves travel fastest through solids and slowest through gases. Thats because particles are closest together in solids and farthest apart in gases. When particles are farther apart, it takes longer for the energy of the disturbance to pass from particle to particle. | text | null |
L_0743 | measuring waves | T_3728 | The organizers of the famous Maverick surf contest have voted that the conditions are right for hanging ten this weekend. The monster waves at Mavericks attract big wave surfers from around the world. But what exactly makes these Half Moon Bay waves so big? For more information on waves, see http://science.kqed.org/quest/video/scie MEDIA Click image to the left or use the URL below. URL: | text | null |
L_0744 | wave interactions and interference | T_3729 | Waves interact with matter in several ways. The interactions occur when waves pass from one medium to another. Besides bouncing back like an echo, waves may bend or spread out when they strike a new medium. These three ways that waves may interact with matter are called reflection, refraction, and diffraction. Each type of interaction is described in detail below. For animations of the three types of wave interactions, go to this URL: | text | null |
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