Simple Machines PDF

What are some examples of simple machines? Mechanical Systems 3.1 Simple & Compound Machines Machines Machines help people use energy more efﬁciently. A machine helps us do work. The earliest machines were simple devices to make work easier; like moving a large rock or moving a load up an incline, splitting wood or lifting materials up to a working area above the ground. These simple machines depended on people or animals as their source of energy. Simple Machines A simple machine is a tool or device made up of one basic machine. There are six types of basic machines. Inclined Plane (Ramp) an angled surface used to help move a load up or down over a horizontal distance Wedge two inclined planes joined back to back used to separate objects or hold an object in place Screw a cylindrical wedge with an inclined plane wrapped around it used to move objects or material also used to fasten materials together Wheel and Axle a larger-diameter wheel attached to a smaller-diameter cylinder the rotation of one is transferred to the other Pulley a wheel and axle that supports a rope, cable or chain used to help move loads vertically or change the direction of a force Class One Lever a beam that pivots around a fulcrum to help move a load the fulcrum sits between the force and the load used for changing the direction of a force (e.g., push down and the load moves up) Class Two Lever a beam that pivots around a fulcrum to help move a load the load sits between the force and the fulcrum used for lifting heavy loads or generating a lot of output force Class Three Lever a beam that pivots around a fulcrum to help move a load the effort force is applied between the load and the fulcrum used for moving loads fast, far and with precision Types of Levers Every lever has 3 components: the load (what is being lifted), the effort (the force applied) and the fulcrum (the pivot point). https://www.youtube.com/watch?v=fzljPiPy9n w The class of lever is determined based off of what component is in the middle. 123 FLE Examples Class 1: Fulcrum in middle Scissors - Seesaw Class 2: Load in middle Wheelbarrow - stapler Class 3: Effort in middle Hockey stick - hammer Compound Machines Compound Machines combine multiple simple machines together. Scissors are a compound machine. class one lever wedge graphic by Clker-Free-Vector-Images, Pixabay Which simple machines do you see? graphic by OpenClipart-Vectors, Pixabay Which simple machines do you see? class two wheel and axle lever graphic by OpenClipart-Vectors, Pixabay Identify the simple machines that make up this compound machine Energy Mechanical systems, or machines, are made up of multiple parts that work together to perform a function. They require energy input to perform tasks, but the energy input varies depending upon the design of the system. Energy input is what type of energy we have to use to make the machine work. Kinetic Energy Kinetic energy is the energy of movement. Anything that moves has kinetic energy. Many machines require us to move in order to work. Chemical Energy Many modern machines run on some kind of fuel. They get energy from breaking apart the chemical bonds in the fuel that they burn. These machines run on chemical energy. Electrical Energy Most of our household machines run on electricity. Anything that plugs into the wall, or has solar panels would run on electric energy. What type of input energy does this vacuum use? What type of input energy does a hammer require? What type of input energy does a human require? Analyzing Machines Each part of the mechanical system (machine or device) contributes to its overall functioning. When analyzing a mechanical system, there are various levels of speciﬁcity to consider. Systems A system is a complete device with an overall function. In this case, the can opener relies on the kinetic energy of someone squeezing the device closed around the rim of the can and then cranking the handle to perform its function: cutting open a can. Subsystems A subsystem is a collection of parts that serve a speciﬁc function in a device. One of the subsystems of a can opener is its cutting mechanism. The gear grips the can while the blade cuts into it, detaching the top of the can from the rest. The assembly is held together by a screw. Components Components are the individual parts that make up a system or subsystem. Many components operate as simple machines. In a can opener, the turning handle operates as a wheel and axle. This is one of many components in the system. Device Analysis Device Name: - Hand Drill Device Function: Input Energy: Device Analysis Identify the two subsystems that make up the drill. Device Analysis Label three components that act as simple machines ‭Mechanical Systems Topic 1 Vocabulary‬ ‭Term‬ ‭Definition‬ ‭Lever‬ ‭ simple machine made of a rigid beam and‬ A ‭a fulcrum‬ ‭Fulcrum‬ ‭The point on which the beam pivots‬ ‭Load‬ ‭Force extended on a surface or a body‬ ‭Effort Force‬ ‭An input force‬ ‭Effort Arm‬ ‭ istance from the effort force and load to the‬ D ‭fulcrum‬ Concept 2: Work and Mechanical Advantage What is the purpose of machines? Machines help us do work. Work is related to energy. Energy is the ability to do or change something. Work is done when a force is used to move an object a certain distance. Ex. Shovelling snow across your driveway is doing work. All machines make work easier by one of four ways: 1. Increasing force ○ Ex. Using a screwdriver 2. Increasing speed ○ Using a hockey stick to shoot a puck 3. Changing the direction of force ○ Using a pulley system, pulling down instead of up against gravity 4. Transferring energy ○ Bike chains, transferring energy from the pedals to the wheels. Work = Force x Distance Units: Work is measured in Joules (J) or Newton Meters (Nm) Force is measured in Newtons (N) Distance is measured in meters (m) When solving equations in science: Step 1: Identify what you are solving for (the unknown). Step 2: Write down given information. Step 3: Determine the formula. Plug the values into the formula. Use proper units of measure. Calculate your answer, include the proper unit. Practice calculating work in notebook Which of these is more work? 1. a. A force of 12 N is applied to move an object 5m. b. A force of 40 N is applied to push a load 1 m. Which of these is more work? 2. a. It takes 36 N to hold a box in the air for 2 minutes. b. It takes 1 N to move a box 1 m. Mechanical Advantage REMEMBER: machines help us make work easier by increasing force, changing direction, increasing speed, or transferring energy. Machines take the energy we put in and change it. How much easier a machine makes work is called it’s Mechanical Advantage. Mechanical Advantage is the ratio of force produced by a machine (the load or output force) compared to the force applied to the machine (the effort or load force). The general MA of a machine can be calculated using this formula: There are 3 different outcomes related to mechanical advantage: Ratio Force Results MA > 1 Force in < Force out Mechanical advantage present MA = 1 Force in = Force out No mechanical advantage but helps change direction MA < 1 Force in > Force out Negative mechanical Advantage, help do a job faster by covering more distance Mechanical Advantage Continued We don’t always know the effort and load forces on a machine to use the general mechanical advantage formulas. Luckily most simple machines also have speciﬁc formulas that can be used just for that machine using measurements. The mechanical advantage The mechanical advantage of a of a lever is increased when wheel is increased when the the effort arm is longer! wheel is larger and the axle is smaller. The mechanical advantage of an inclined plane is increased by having a lower height and a longer plane distance. Pulleys Calculating the MA for a pulley is a little different. In this machine, you count the number of supporting ropes in the pulley system. These are all the ropes that are sharing the weight of the load. U N I T Mechanical Systems How many mechanical systems have you used today? You may not realize it, but you use mechanical systems all the time to do simple tasks. When you ride a bicycle, open a can, or sharpen a pencil, you have used a mechanical system to help you complete a task. All mechanical systems have an energy source. The energy could come from electricity, gasoline, or solar energy, but often the energy comes from humans. (Remember that huge structures such as the pyramids were built solely using human power!) The energy needed to move this bicycle and this plane, for example, comes from a pedalling human. Can you see how machines help us perform tasks we might ﬁnd difﬁcult to do otherwise? Imagine opening a can without a can opener. Could you ﬂy without a plane or other type of aircraft? In this unit, you will learn how some small, human-powered mechanical devices work. You will see that tools as simple as a pair of scissors function on the same principles as massive equipment powered by ﬂuid pressure and heat engines. You will discover the main factors in the efﬁcient operation of mechanical systems. You will also design and build your own mechanical devices — including some powered by hydraulics and pneumatics — and investigate their efﬁciency. Finally, this unit examines how machines have changed as science and technology have changed. 266 Unit Contents TOPIC 1 Levers and Inclined Planes 270 TOPIC 2 The Wheel and Axle,Gears, and Pulleys 285 TOPIC 3 Energy, Friction, and Efficiency 296 TOPIC 4 Force, Pressure, and Area 304 TOPIC 5 Hydraulics and Pneumatics 313 TOPIC 6 Combining Systems 326 TOPIC 7 Machines Throughout History 332 TOPIC 8 People and Machines 342 U N I T 4 How do we use How many machines have you used today? machines to do work and How do we use mechanical devices such as to transfer energy? levers and pulleys to help us perform tasks? In Topics 1–3, you will learn about lots of How can we design and mechanical devices. use machines efficiently and responsibly? How have machines changed over time? How can the pressure of fluids be used to operate a machine such as this amusement park ride? In Topics 4–6, you will learn how fluids are used in mechanical systems, and how many systems — even your body — are a combination of several smaller systems working together. 268 MHR Mechanical Systems How have mechanical devices changed over time? How do changes in society and the environment affect the mechanical devices we design? In Topics 7–8, you will explore how and why mechanical devices change over time. roject, d p ag es 3 5 4 –355, Unit 4 P Rea ct this tin g To o ls.” You will condu “Ad ap –8. yo u h av e co m pleted Topics 1 project after e ad th e C h alle n ge posed on pag Carefully re that you 5 4. Sta rt th in king about items a 3 ad ap t fo r an older person or might like to. a p h ys ic al injury or disability person with or es, newspapers, Look in magazin u gu es fo r ex am ples of things yo catalo s in a t w an t to ad ap t. Save your idea migh g File.” “Project Plannin t p le sk et ch es of how you migh Make sim file. ite m , an d ke ep them in your adapt an Unit 4 Preview MHR 269 T O P I C 1 Levers and Inclined Planes A B In a dictionary, find the origin of the word “lever.” Then look up the meaning of the word “leverage” and use it in a sentence. Figure 4.1A and B How are the screwdriver and the teeter-totter alike? If you were to exert a force on a screwdriver, the screwdriver would exert a force on something else, as shown in Figure 4.1A. Both the What is the largest screwdriver and the teeter-totter (shown in Figure 4.1B) act as levers. object you have ever As you learned in previous studies, a lever is a simple machine that tried to lift? At the changes the amount of force you must exert in order to move an time, did you think that object. It consists of a bar that is free to rotate around a ﬁxed point. there must be an easier This ﬁxed point, the fulcrum, supports the lever (see Figure 4.2). The way to do this? Write fulcrum is the lever’s point of rotation. The force that you exert on a your responses to lever to make it move is called the effort force. This term is used to these questions in your describe the force supplied to any machine in order to produce an Science Log. As you action. The load is the mass of an object that is moved or lifted by a study this unit, you will machine such as a lever. In other words, the load is the resistance to discover some “better movement that a machine must overcome. The distance between the ways” to lift large objects and move fulcrum and the effort force is called the effort arm. The distance mechanical devices. between the fulcrum and the load is called the load arm. load effort force load arm effort arm For tips on making a great Science Log, turn fulcrum to Skill Focus 3. Figure 4.2 A lever is a simple machine consisting of a bar that rotates around a fixed point, the fulcrum. 270 MHR Mechanical Systems You can discover levers in many different situations. Levers are sorted into three classes. The class a lever belongs to depends on the Have you ever rowed or position of the effort force, the load, and the fulcrum, as shown in sailed a boat? The oars in Figures 4.3A, B, and C. As the photographs show, different classes of a rowboat and the rudder levers are used for different purposes. of a sailboat are both Class 1 levers. What class In a Class 1 lever, the fulcrum is between the effort and the load. A of lever do you think a pair of scissors is an example of a Class 1 lever. This class of lever can canoe paddle is? be used either for power or for precision. A Class 2 lever, such as a wheelbarrow, always exerts a greater force on the load than the effort force you exert on the lever. In this type of lever, the load is between the effort and the fulcrum. In a Class 3 lever — a hockey stick, for example — the effort is exerted between the fulcrum and the load. When using a Class 3 lever, you must exert a greater force on the lever than the lever exerts on the load. However, the load can be moved very quickly. Figure 4.3A An example of a Class 1 lever Figure 4.3B An example of a Class 2 lever Figure 4.3C An example of a Class 3 lever Levers and Inclined Planes MHR 271 S K I L L C H E C K Initiating and Planning Performing and Recording 4-A Analyzing and Interpreting Communication and Teamwork Levers in Action How does the position of the fulcrum affect the effort force you must exert to lift a load? Do you have to exert a greater effort force on a Class 2 or a Class 3 lever to lift the same load? In this investigation you will contrast different types of levers. Hypothesis Form a hypothesis about how the position of the fulcrum and the location of the load affect the amount of effort force you must exert to lift the load. Apparatus sturdy board brick (or similar heavy mass) strong string Procedure Place the board on a desk Place the brick on the desk Try to lift the brick by push- or work surface, with half on top of the end of the ing down on the free end of its length extending over board. This makes a Class 1 the board. the edge. lever, with the edge of the desk acting as the fulcrum. CAUTION Handle the brick carefully so it does not fall on your foot. 272 MHR Mechanical Systems Repeat step 3 with most of Now tie the brick to the Finally, tie the brick to the board’s length on the board so that the brick the far end of the board. desk surface. hangs underneath it. Put one This makes a Class 3 lever. end of the board on the desk Try lifting it while holding and hold the other end. This the board in two or three makes a Class 2 lever. Try different places. You will to lift the brick while it is need to make sure the end hanging at two or three of the board stays in place different places along the on the desk. board. Analyze 1. (a) Which class or classes of lever exert(s) a load force greater than your effort force? Repeat step 3 with most of (b) Which class or classes of lever exert(s) a load force less the board extending over than your effort force? the edge of the desk. 2. Does a Class 1 lever always exert a load force that is greater Compare the amount of than your effort force? effort force you must exert 3. Which variable(s) was (were) the responding variable(s) in in each position in steps this investigation? Which variable was manipulated? 3 to 5. Record your observations. Conclude and Apply 4. Write a statement comparing the advantages of Class 1, Class 2, and Class 3 levers. Levers and Inclined Planes MHR 273 Bones and Muscles: Built-in Levers Every time you move a ﬁnger, arm, or toe, you are using a lever. Your bones act as levers and each of your joints acts as a fulcrum. Tendons attach muscles to your bones. When a muscle contracts, the tendon exerts an effort force on the bone. The load might be something that you are lifting or pulling. The load could also be your own body; for example, when you do a knee bend. Most of the levers in your body are Class 3, but you can ﬁnd Class 1 and Class 2 levers as well (see Figure 4.4). A B C Figure 4.4 Your body’s system of muscles and bones contains natural examples of levers, including Class 1 (A), Class 2 (B), and Class 3 (C). Look at the body levers shown in Figures 4.5A, B, and C. Decide the class of each lever. before after before before calf biceps triceps muscle elbow elbow contact contact point point after ankle after contact point A B C Figure 4.5A The calf muscle provides Figure 4.5B The biceps muscle provides Figure 4.5C The triceps muscle provides the effort force. Assume that a body the effort force. The hand is lifting a 15 the effort force. The hand is pulling the weight of 600 N is the load. N object. rope down with a force of 30 N. 274 MHR Mechanical Systems An Arm in Space One of the most exciting technological applications of levers is the Space Shuttle Remote Manipulator System, shown in Figure 4.6A. This system is usually called the Canadarm. It functions much like a human arm, and it was designed and built in Canada. The “joints” are moved by gears. As the gears turn, they move the “arms,” which resemble levers. Figure 4.6A The Canadarm is an amazing application of gears Figure 4.6B The Space Station Mobile Servicing System will be and levers in outer space. equipped with a smaller two-armed robot – the SPDM – to do complex repair jobs in space. The Canadarm is a valuable addition to the space shuttle program because it helps launch and recover satellites from the shuttle’s cargo bay. One of the Canadarm’s most important missions was the repair of the Hubble Space Telescope. This orbiting telescope can see farther and more clearly than any ground-based optical telescope. (You may have learned about the Hubble Space Telescope in Unit 3.) A more complex version of the Canadarm — the Space Station Mobile Servicing System — is shown in Figure 4.6B. This system will assist in assembling and maintaining the International Space Station. Do you remember the The base of the system will move along rails spanning the entire length difference between mass of the space station. When stretched out straight, the arm will be more and weight? Weight is a force, and it is measured than 17 m long. It will be equipped with a smaller two-armed robot in units called newtons that can do delicate repair jobs that astronauts themselves have done on (N). The mass of an space walks until now. object is the measure of Sixteen countries, includ- the amount of material in Internet: ing Canada, Russia, www.school.mcgrawhill.ca/resources/ it. Mass is measured in Japan, and the United grams or kilograms. You Learn more about the Canadarm and the International measure weight with a States, are co-operat- Space Station by going to the above web site. Go to spring scale, or a force ing in the planning Science Resources, then to SCIENCEFOCUS 8 to meter. You measure mass and assembling of the find out where to go next. with a balance. International Space Station. Levers and Inclined Planes MHR 275 What Is Work? Does the title to this section sound like a silly question? Everyone knows what work is! When you study for two hours, you have done a As you continue your lot of work. Cleaning your room always seems like a lot of work. studies in science, look Carrying your backpack full of books is work. Or is it? for more words that have scientific meanings that In everyday language, work can mean many different things. are different from their However, in science, work has a special meaning. When you exert a everyday meanings. Can force on an object and move that object some distance in the direction you think of any of these of the force, you do work on the object. For example, in Investigation words that you have 4-A, you exerted an effort force on the lever and moved it. You did already learned in addition work on the lever. In turn, the lever exerted a force on the load (the to work? brick). The lever did work on the brick. In science, work is deﬁned as the product of the force exerted times the distance moved. Work = Force Distance Work is energy in action. Like energy, work is measured in units called joules (J). The joule is named after English scientist James Prescott Joule (1818–1889). In Unit 2, you learned that 1 N is approxi- mately the weight of a 100 g mass. When you lift a 1 N weight a distance of 1 m, you do 1 J of work. To practise using the formula, assume that you exerted a force of 2.0 N on the lever and moved it a distance of 0.6 m. Calculate the work. W=F d W = 2.0 N 0.6 m W = 1.2 J You did 1.2 J of work on the lever. If the lever exerted a force of 6.0 N on the brick and moved it a distance of 0.20 m, how much work did the lever do on the brick? Figure 4.7A Somehow Think once more about carrying your backpack full of books down Olivia has to get a box the hall at school. Assume that your full backpack weighs 40 N. If you into the back of this truck. Is lifting the box straight walk down the hall a distance of 16 m, how much work did you do on up and carrying it to the your books? According to the scientiﬁc deﬁnition, you did no work! back of the truck the Why? You were exerting a force upward on the backpack so it would best option? not fall on the ﬂoor. However, you did not move upward. You moved it in a horizontal direction. The Inclined Plane Figure 4.7B Olivia used an An inclined plane is a ramp or a slope that reduces the force you inclined plane to help her need to exert to lift something. Inclined planes are also machines. load the box of camping Look at the illustrations on the left. Olivia has the task of lifting a gear into the truck. The inclined plane decreased 50 kg box of camping gear into the back of the truck. The distance the effort force Olivia from the ground to the back of the truck is 1 m (see Figure 4.7A). needed by increasing the Lifting the box straight up and carrying it to the truck would be distance through which her difﬁcult. However, if Olivia used a board to make a ramp, as she does effort force was applied. in Figure 4.7B, she could probably push the box up. 276 MHR Mechanical Systems Find Out Easy Does It! Why is it easier to climb a gentle hill than a 7. Repeat this procedure for ramp heights of steep mountain trail or a cliff face? How does 0.10 m, 0.15 m, 0.20 m, and 0.25 m. Use a the work you put into a machine (the work stack of books to create the ramps. input) affect the work that the machine does (work output)? Try this activity to answer these questions. Materials spring scale toy car or dynamics cart string tape (optional) flat board at least 0.5 m long metre stick stack of books Procedure Performing and Recording 1. Copy the data table shown here into your notebook. Work Work Height of Weight output (J) Effort Length of input (J) ramp (m) (N) W = N × m force (N) ramp (m) W = N × m 2. Attach the spring scale to your car using 0.05 the string. You may want to attach the 0.10 string to the car with the tape. 0.15 3. Measure the weight of your car. Record 0.20 this information in your data table. 0.25 4. Calculate the amount of work needed to lift the car for each height in the table without What Did You Find Out? Analyzing and Interpreting using a ramp. Record this information 1. Which took more force, lifting the car under the column “Work output (J).” straight up or using the ramp? 5. Using a thin book to prop up the board, 2. Write a statement explaining how the force make a ramp that has one end raised 5 cm needed to pull the car up the ramp relates (0.05 m). Use the spring scale to pull the to the length of the ramp. car up the ramp. Pull at a slow, steady speed. Record the effort force needed to 3. Write a statement explaining how the force lift the car by pulling it up the ramp. needed to pull the car up the ramp relates to the angle of the ramp. 6. Measure the length of the ramp. Then calculate the amount of work required to 4. Did it require less work to pull the car up pull the book up the ramp. This is the the ramp than it did to lift the car to the work input. same height directly? Explain your answer. Levers and Inclined Planes MHR 277 Work Input and Work Output When you do work on a machine such as a lever, the machine does work on a load. The work you do on the machine is called input work. The work the machine does on the load is the output work. You may have noticed, when you did Investigation 4-A, that when your effort force was small, the distance you pushed on the lever was large. At the same time, the distance that the lever lifted the load was small. How do you think that the input work compares to the output work? You probably discovered, in the Find Out Activity, that your input work on the ramp was nearly the same or larger than the output work. As you continue to study mechanical systems, you will discover that this is always true. A machine never does more work on the load than you do on the machine. Why, then, do we often say that machines make work easier? Machines make work easier because they change the size or the direction of the force exerted on the machine. Think about this. Could you lift a small, compact car a distance of one metre off the ground? Could you lift yourself (climb) up ﬁve ﬂights of stairs? The two situations represent about the same amount of work. What Is Mechanical Advantage? Mechanical advantage is the comparison of the force produced by a machine to the force applied to the machine. In other words, mechani- cal advantage is the comparison of the size of the load to the size of the effort force. The smaller the effort force compared to the load, the greater the mechanical advantage. You can use the following formula to calculate mechanical advantage: Load force (FL) Mechanical Advantage (MA) = Effort force (FE) Suppose you are a passenger in a truck that gets stuck in mud. You and the driver use a tree branch as a lever to lift the truck out of the mud, as shown in Figure 4.8. If you apply an effort force of 500 N to the branch, and the back of the truck weighs 2500 N, then the mechanical advantage of the branch-lever is 5. Note that no units are used to express mechanical advantage because it is a ratio. Figure 4.8 The mechanical advantage of this branch- Load force (FL ) lever is 5. Mechanical Advantage (MA) = Effort force (FE) effort force = 2500 N 500 N 500 N =5 lever fulcrum load force 2500 N 278 MHR Mechanical Systems The branch-lever has exerted a force 5 times greater than the force you exerted on it. This means the branch-lever made the job of lifting the truck 5 times easier. Any machine with a mechanical advantage What’s the advantage of greater than 1 allows the user to move a large load with a relatively using a bicycle if it has a small effort force. mechanical advantage A machine can also have a mechanical advantage that is less than 1. that is less than 1? The Imagine you are riding your bicycle. You exert an effort force of, say, advantage is that it caus- 736 N downward as you push on the pedal. The resulting load force es the tire to turn faster that causes the bicycle to move forward is 81 N. The mechanical than the pedals and the advantage of the bicycle is calculated as follows: bicycle moves faster than your pedalling speed. You gain a speed advantage. Load force (FL ) Mechanical Advantage (MA) = What other devices have a Effort force (FE) mechanical advantage = 81 N less than 1? Write your 736 N ideas in your Science Log. = 0.11 Finally, a machine may have a mechanical advantage equal to 1. For example, suppose the effort force needed to raise a ﬂag up a ﬂagpole is 120 N. The load force — the ﬂag plus the rope — is also 120 N. Therefore, the mechanical advantage of the pulley on the ﬂagpole is 1: Load force (FL ) Mechanical Advantage (MA) = Effort force (FE) = 120 N 120 N =1 Some machines do not have any effect on the effort force that you exert. They simply change the direction of the effort force. For example, when you pull down on the cord of window blinds, the blinds go up. Only the direction of the force changes. The effort force and the load are equal, so the mechanical advantage is 1. Try to think of other mechanical devices that have a mechanical advantage of 1. Write your ideas in your Science Log. A crafty coyote is trying to use a catapult to launch a heavy rock. The rock, with a mass of 1000 kg, sits on one end of a plank. The coyote figures that if he jumps on the other end of the plank, his 25 kg mass will be enough to launch the rock into the air. Calculate the mechanical advantage the catapult must have for the coyote’s plan to work. Levers and Inclined Planes MHR 279 Find Out Sharpen Up with Scissors Is there a mechanical advantage to using CAUTION When using scissors, always scissors? Is one way of using scissors easier cut away from your body. than another? Make a prediction about whether it takes less effort force to cut 2. Open the scissors wide, put the cardboard cardboard with the tip of the blades or with close to the hinge of the scissors, and the base of the blades near the hinge. again make a cut. Safety Precautions What Did You Find Out? Analyzing and Interpreting 1. Does one method make cutting the card- board easier than the other method? Materials 2. Explain your observations based on what scissors you have learned about levers, effort force, piece of heavy cardboard or folded paper and mechanical advantage. Procedure Performing and Recording 3. Describe how the effort arm relates to 1. Test your prediction. Try to cut the the load arm in these two photographs. cardboard with the tip of the scissors. You have been learning about different types of levers and how they give us a mechanical advantage. Create a web tutori- al to teach other students about these machines and the ways they help us do work. In your tutorial, simulate the action of the three different types of levers. Your simulated levers can be simple machines, such as the ones shown here, or they can be parts of your body. Include a quiz and an answer key for self-checking. 280 MHR Mechanical Systems Another Way to Calculate Mechanical Advantage Levers can exert a force on a load that is either greater than or less than the effort force you exert. If the load is less than the effort force, the lever’s mechanical advantage is less than 1. For example, a mechani- Surgeons use special cal advantage of _21 shows that your effort goes only half as far compared tools in a type of to a lever with a mechanical advantage of 1. microsurgery some- The concepts of mechanical advantage and work can be linked. times called “keyhole Imagine that you are trying to lift a heavy boulder, as the coyote is on surgery” because only page 279. The closer you are to the fulcrum (the smaller rock), the a small incision is needed. A long tube is harder it is to lift the boulder. The longer the effort arm (the distance pushed through the between the fulcrum and the effort), the less effort it will take to lift the incision to the part of boulder. The longer effort arm gives you a mechanical advantage. the patient’s body Recall that Work = Force Distance. You trade distance for force — requiring surgery. Fine you move the board farther, but moving it is easier. However, the amount wires running through of work you do is the same. This suggests another way to calculate the the tube operate tiny levers to cut and mechanical advantage of levers: sew as needed. The Load force (FL ) Effort arm surgeon watches the Mechanical Advantage (MA) = = operation on a televi- Effort force (FE) Load arm sion screen connected to a tiny camera at the If the effort arm of the branch-lever mentioned on page 306 were end of the tube. 3 m, and the load arm were 0.3 m, then the mechanical advantage would be calculated as follows: Effort arm (MA) = Load arm = 3m 0.3 m = 10 Using the branch as a Class 1 lever allows the effort force to be multiplied by 10. Although it might seem strange, there are situations in which you might want to increase the force that you yourself exert. For example, you might need a machine to perform a delicate precision task. Think about how tweezers work as you study this photo- graph. Which class of lever do they use? Infer whether the mechanical advantage of tweezers will be greater than 1, equal to 1, or less than 1. Levers and Inclined Planes MHR 281 Speedy Levers When you calculated mechanical advantage, you learned that you can use Class 1 levers to increase your effort force. You can exert only a little force to achieve an incredible result. (This is why you can use a simple Class 1 lever to lift very heavy objects.) Class 3 levers exert a force on the load that is smaller than the effort force, so why would you ever use such as lever? The advantage of a Class 3 lever is that the force will move the load a greater distance and at a faster speed. That is why you hit a hockey puck with the end of a metre-long stick. Speed is the rate of motion, or the rate at which an object changes position. Look at the baseball pitcher and the pizza chef in Figures 4.9A and B. In both cases, the triceps muscle moves only a small amount to produce the effort force needed to make the hand move rapidly through a relatively large distance. The structure of the levers in the human body makes it possible to perform delicate tasks with precision, as well as major tasks requiring tremendous speed and ﬂexibility. If you need tips on how to design an experiment, turn to Skill Focus 6. A B Figure 4.9A How can a small contraction Figure 4.9B Why does the spinning pizza (shortening) of the triceps muscle produce the dough remain more or less in the same place? long, fast movement of the pitcher’s hand? Most of the levers inside your body have a mechanical advantage smaller than 1. Therefore, your muscles usually have to exert a greater force on the lever (bone) than the lever (bone) can exert on the load. With a partner, design an experiment that tests what you have learned about the speed advantage of Class 3 levers. Use simple materials, such as marbles and a ruler. Write a hypothesis, and the steps that would test your hypothesis. What variable would you manipulate? How would you measure the speed and distance? 282 MHR Mechanical Systems Machines Made to Measure Industrial designers study the dimensions of the human body in great detail to make sure that every part of a machine or a product — such as the ones shown in Figure 4.10 — will ﬁt the person using it. Body Imagine you are an ergonomist (an weight, height, size, age, and sometimes gender are factors taken into ergonomics designer) account when designing products. These products can range from cars working on the to ofﬁce furniture to light switches. The science of designing machines International Space to suit people is called ergonomics (from the Greek words ergon, Station program. What meaning “work,” and nomos, meaning “natural laws”). sorts of problems might you have to solve? Remember that the astronauts will be working in cramped positions as well as in weightlessness. Write your ideas in your Science Log. B A Another way to avoid C carpal tunnel syndrome Figure 4.10 This space suit, child’s car seat, and assembly line in a factory have is to get rid of the key- all been designed to ensure that they are easy, comfortable, and safe for people board altogether and to to use. operate the computer using a special pen-like Ergonomics is especially important in the design of work environments device, which keeps the where occupational safety is an issue. For example, a common work- wrist flat. “Palm pilots” place disorder known as carpal tunnel syndrome causes numbness (hand-held computers) are already pioneering and pain in the thumb and ﬁrst three ﬁngers. Carpal tunnel syndrome this approach. Perhaps results from repetitive movements of the ﬁngers, such as working at a one day home computers computer keyboard. If the tendons that attach muscles to bones in the will be able to “read” wrist become irritated, they swell and start to squeeze the nerve inside your handwriting — the carpal tunnel. If the condition is not treated soon after the symp- however messy it is! toms appear, severe pain as far up as the shoulder can result. The Voice-activated computer programs are also reduc- damage could become permanent. The most common treatment for ing the incidence of carpal tunnel syndrome is a brace that holds the wrist straight. This carpal tunnel syndrome. prevents irritation of the tissues near the carpal tunnel. Levers and Inclined Planes MHR 283 Looking Ahead Dr. Janet Ronsky knows the human knee joint. And that information helps doctors The simple machines like the back of her hand. She is a biome- decide how to treat the patient. you have learned about chanical engineer and an associate For Janet, working in bioengineering is the in this Topic are used professor at the University of Calgary. Her perfect career. “Once I discovered I could to make work easier. research on the knee joint helps doctors and apply engineering to medical problems,” she Turn to “Adapting other researchers understand how the shape explains, “and possibly make a difference in Tools” on page 354 to of a person’s bones may contribute to people’s everyday lives, I was hooked!” She preview the project you degenerative joint diseases such as takes her work very seriously, and she’s not will be undertaking at osteoarthritis. Many specialists believe that the only one who thinks it is important. In the end of this unit. the bones of some people's joints press 1999, Dr. Ronsky was presented with the Start thinking of a tool together in an unusual way as they walk. McCaig Program Development Award by the or utensil you might This may wear down the cartilage, the Calgary Regional Health Authority. She was want to adapt using the cushioning material between those bones, also awarded a Natural Science and knowledge you have and result in joint problems. Engineering Research Council of Canada gained so far. Dr. Ronsky and her research team have (NSERC) Women's Faculty Award in 1994. found a way to analyze the surface of the joint bones while a person is walking. This is important because the contact between the bones changes over the course of the walking motion. The research team uses medical imaging along with high-speed camera and video systems that track the movement of the body parts. Other special- ized equipment allows them to measure the force a person applies to different parts of the joint as they walk. By analyzing the three types of information, Dr. Ronsky can predict what is happening inside the patient's knee TOPIC 1 Review 1. Classify the levers in the illustrations as Class 1, Class 2, or Class 3. 2. How much work, in joules, must you do to lift an elephant weighing 60 000 N up 1.5 m onto the back of a truck? 3. You have found a ramp to lead up to the back of the truck. Will you and your team need to exert more, less, or the same forces as in question 2? 4. If you exert a force of 100 N on a hockey stick, and the stick exerts a force of 20 N on the puck, what is the mechanical advantage of the stick? 5. If the “effort arm” distance for the hockey stick in question 4 (between your “fulcrum” hand and your pushing hand) is 25 cm, how long is the stick? (Use your answer to question 4.) If your hand is pushing at a speed of 20 km/h, how fast will the puck move? 6. Thinking Critically Think of a practical use for a lever with a mechanical advantage of 1. Draw a sketch of this lever in action. 284 MHR Mechanical Systems T O P I C 2 The Wheel and Axle, Gears, and Pulleys Earlier, you discovered that you can lift a heavy load as long as you can ﬁnd a lever that is long enough and strong enough to do the job. Sometimes, however, levers are not practical, as shown in Figure 4.11. Fortunately, there are many other kinds of machines that can give you a mechanical advantage great enough to move a heavy load with a much smaller effort force. Think about this question: How could you modify a lever to make it shorter, but still Figure 4.11 No one would able to move a load over a longer distance? Look for clues in Figure ever try to lift an elephant like this! 4.12A, which shows a person loading a motor boat onto a boat-trailer. A Lever That Keeps on Lifting The device the person is using to move the boat is called a winch. The handle of a manual A winch consists of a small cylinder and a crank or handle. Study pencil sharpener and the Figure 4.12B to see how a winch works. Notice that the axle of the reel on a fishing rod are winch is held in place and acts like a fulcrum. The handle is like the examples of winches. effort arm of a lever. Exerting a force on the handle turns the wheel. This motion is much like the effort force on a lever. However, you do not reach “bottom” with the handle. You just keep turning. load arm (radius of cylinder) fulcrum d effort arm loa (length of handle) effort A B Figure 4.12 A winch makes loading a boat onto a trailer relatively easy. Notice that the radius of the wheel — the distance from the centre of the wheel to the circumference — is like the load arm of a lever. The force that the cable exerts on the wheel is like the load on a lever. Since the handle is much longer than the radius of the wheel, the effort force is smaller than the load. Using a winch is like using a short lever over and over again. The Wheel and Axle, Gears, and Pulleys MHR 285 The Wheel and Axle A winch is just one example of a wheel-and-axle device. As you can see in Figure 4.13, wheel-and-axle combinations come in a variety of shapes and sizes. The “wheel” does not even have to be round. As long as two turning objects are attached to each other at their centres, and one causes the other to turn, you can call the device a wheel and axle. You can hardly open your eyes without seeing a wheel-and-axle machine of some sort. Study Figure 4.13 and identify the wheel-and- axle devices. Remember that some instruments or machines have more than one wheel-and-axle combination. The wheel and axle is more convenient than a lever for some tasks, and, like a lever, it provides a mechanical advantage. A B C Figure 4.13 Each of these objects contains a wheel Speed and Action and axle. Gaining a mechanical advantage is one beneﬁt of using a wheel-and- axle device. Just like a lever, a wheel-and-axle device can also generate speed, as shown in Figures 4.14A and B. In return, however, these machines require a large effort force and produce a smaller force on the load. Figure 4.14A Look at the pedals and the Figure 4.14B What are the possible benefits of front wheel on this tricycle. Is the effort force the huge wheel on this old-fashioned bicycle? exerted on the wheel or the axle? What does the clown get in return for the effort put into the machine? 286 MHR Mechanical Systems Gearing Up A wheel-and-axle device provides speed for a race A car zooming around a track. However, the wheel and the axle are attached to each other, so each makes the same number of rotations every second. Suppose you wanted to make one wheel rotate faster than another wheel. For example, a clock has follower gear driver gear a second hand, a minute hand, and an hour hand, each rotating at different speeds from the same point. B A gear is a rotating wheel-like object with teeth around its rim. A group of two or more gears is called a gear train. Two different gear trains (A and B) are shown in Figure 4.15. The teeth of one gear ﬁt into the teeth of another. When the ﬁrst gear turns, its teeth push on the teeth of the second gear, causing the second gear to turn. The ﬁrst Figure 4.15 A gear train gear, or driving gear (often called the driver), may turn because consists of two or more someone is turning a handle or because it is attached to a motor. The gears in contact with second gear is called the driven gear (often called the follower). Can each other. you ﬁnd a gear train in Figure 4.16? Figures 4.17 and 4.18 on page 288 illustrate two other applications of gears. Find out what gears can help you do in the next activity. Figure 4.16 This combine features sprockets and belts, as well as a gear train. The Wheel and Axle, Gears, and Pulleys MHR 287 Figure 4.17 This diagram shows how the gears inside an old- Figure 4.18 The gears inside a large telescope are designed so fashioned clock ensure that the minute hand makes exactly that the telescope can track the constant slow motion of stars 60 full rotations when the hour hand makes one full rotation. across the sky with incredible precision. Find Out Turnaround Time How many times does the follower gear turn 4. Divide the diameter of the larger gear by when the driver gear makes one full turn? the diameter of the smaller gear. Record Does the number of rotations depend on how your answer. Compare this number with much larger the driver gear is? the number you recorded in step 2. Materials 5. Count the number of teeth on each gear. set of gears of different sizes — for example, Divide the number of teeth on the larger from a Spirograph™ or Lego Technik™ set gear by the number of teeth on the smaller gear. Record your answer. Compare this felt tip pen and ruler number with the numbers you calculated Procedure Performing and Recording in steps 2 and 4. 1. With a felt tip pen, make a mark on one What Did You Find Out? Analyzing and Interpret tooth of each of the two gears, at the spot 1. Why does the smaller gear complete one where they touch. full rotation before the larger gear does? 2. Turn one gear and count the number of (Look at the felt tip marks as the gears times the smaller gear turns when the go around.) larger gear makes one full turn. Record 2. If the larger gear had three times as many this number. teeth, how many rotations would the small- 3. Measure and record the diameters of each er gear make in one rotation of the larger of the gears. gear? How much bigger would the larger gear be in this case? 3. Explain two different measurements that you could use to predict the numbers of turns a small gear will make every time the large gear makes one full turn. What would you predict about the mechanical advantage of this gear combination? Write a statement that summarizes your conclusion about gears. 288 MHR Mechanical Systems Going the Distance Can one gear turn another gear without touching it? Does this sound impossible? Think about the gears on your bicycle. One set of gears is attached to the pedals and another to the rear wheel. A chain connect- ing the gears allows the front gear to turn the gear on the rear wheel, some distance away. A gear with teeth that ﬁt into the links of a chain is called a sprocket. Figure 4.19 compares gears in contact with each other and gears in a sprocket. A B wheel and pinion (gears in contact) chain and sprockets Figure 4.19 Take a look at this comparison of gears in contact (A) and gears, or sprockets, connected by a chain (B). While the gears in contact turn in opposite directions, the gears connected by a chain turn in the same direction. Each link of a bicycle chain moves the same distance in the same period of time. Thus, if the front sprocket moves the chain a distance equal to 45 teeth, the back sprocket will also move through a distance of 45 teeth. However, the back sprocket may have only 15 teeth and the front sprocket may have 45 teeth. As a result, the back sprocket would make three full turns for every one complete turn of the front sprocket. The relationship between the speed of rotations of a smaller gear and a larger gear is called the speed ratio. In this example, the bicycle has a speed ratio of 3. Here is the formula for calculating speed ratio: Number of driver gear teeth Speed ratio = Number of follower gear teeth In the next investigation, examine the speed ratio of gears in a bicycle. Figure 4.20 This enormous conveyor belt is used at Syncrude Oil Sands in Fort McMurray, Alberta. The belt acts like a chain. Can you see the sprockets? The Wheel and Axle, Gears, and Pulleys MHR 289 S K I L L C H E C K Initiating and Planning Performing and Recording 4-B Analyzing and Interpreting Communication and Teamwork Gear Up for Speed! How do bicycle gears help your bicycle go faster, or help you pedal up a hill? What is the difference between high gear and low gear? Why would you want more than one gear on your bicycle anyway? This investigation will demonstrate how gears on a bicycle can give you a mechanical advantage. Question How does the speed ratio change as you switch between different gears on a bicycle, and how does this affect the force you need to pedal the bicycle? Apparatus bicycle with double set of racing gears Procedure Make a data table like the Count the number of teeth Count the number of teeth one shown below. Give your on each of the front sprock- on each of the back sprock- table a suitable title. You ets. Record these numbers ets. Record these numbers may have to change the in the row of your table to in the column below the number of rows and the right of the heading, heading, “Number of teeth.” columns, depending on the “Number of teeth.” Make Again, make sprocket num- number of sprockets on the sprocket number 1 the ber 1 the largest sprocket. bicycle you are using. largest sprocket. Front sprockets 1 2 3 For tips on creating data tables, turn Back sprockets Number of teeth to Skill Focus 10. 1 2 3 4 5 6 290 MHR Mechanical Systems For each box in the rest of Analyze the table, divide the number 1. What do the data indicate about the number of times the of teeth in the front sprocket back sprocket and the wheels turn when the front sprocket (at the top of the column) by and the pedals make one full turn? the number of teeth in the 2. Explain what you think “high gear” and “low gear” mean. back sprocket (in the ﬁrst column of the table). This 3. If the speed ratio increases when you change gear, will the gives you the speed ratio of mechanical advantage of the bicycle increase or decrease? each gear combination. (Hint: Remember what you learned about trading force for distance or speed.) Conclude and Apply 4. Why do you need to pedal faster to go at the same speed when your bicycle is in a lower gear? 5. Which gear helps you go faster on level ground? Why? 6. Why do you use low gear when going up hills? The Wheel and Axle, Gears, and Pulleys MHR 291 Pulleys Figure 4.21 How does this weight machine allow the woman to lift weights safely and comfortably? You learned in previous studies that a pulley is a grooved wheel with a rope or a chain running along the groove. You can see an example of pulleys in action in Figure 4.21. A pulley is similar to a Class 1 lever. Instead of a bar, a pulley has a rope. The axle of the pulley acts like a fulcrum. The two sides of the pulley are the effort arm and the load arm. Pulleys can be ﬁxed or movable, as shown in Figure 4.22. A fixed pulley is attached to something that does not move, such as a ceiling, a wall, or a tree. A ﬁxed pulley, such as the one used at the top of a ﬂagpole, can change the direction of an effort force. When you pull down on the effort arm with the rope, the pulley raises the object attached to the load arm. Thus, a single ﬁxed pulley simply changes the direction of the motion and makes certain movements more convenient. Once the ﬂagpole pulley is attached, you can raise and lower the ﬂag without ever climbing to the top of the ﬂagpole! A movable pulley is attached to something else, often by a rope that goes around the pulley itself. If a rope is ﬁxed to the ceiling and then comes down around the pulley and back up, you can lift and lower the pulley MA = 1 MA = 2 single fixed pulley single movable pulley itself by pulling on the rope. The load may be attached to the centre of the pulley. Figure 4.22 Pulleys can be fixed or movable. 292 MHR Mechanical Systems Supercharging Pulleys You saw that a wheel-and-axle combination can be compared to a lever. It would seem logical to analyze a pulley in the same way. However, if you imagine a pulley as a lever, you will discover that the “effort” arm and the “load” arm are the same. So how do pulleys help you lift heavy loads? You have seen that a single pulley can make lifting a load more convenient. Combinations of pulleys are required to lift very heavy or awkward loads (see Figure 4.23). The very complex pulley system shown in Figure 4.24 is a combination of ﬁxed and movable pulleys, called a block and tackle. Depending on the number of Figure 4.23 This oil pump pulleys used, a block and tackle can have a large mechanical uses several pulleys and a advantage. You have probably noticed that pulley systems lever to raise and lower the designed to lift very heavy loads have long cables running pump valves to bring the around several pulleys. How can you determine the mechanical oil to the surface. advantage of a compound pulley — one made up of several pulleys working together? To ﬁnd out, perform the investiga- Figure 4.24 A block tion on the next page. As a warm-up, you can also do the MA = 4 and tackle activity below. Find Out Tug of War How can you increase the mechanical Experiment with different numbers of advantage of a pulley? rope windings. Safety Precaution Always wear gloves to protect your hands from rope burn. Materials 2 broom handles or similar smooth poles rope or twine (about 4 m) Procedure Communication and Teamwork 1. Two students hold the upright broom What Did You Find Out? Analyzing and Interpr handles between them, side by side. 1. Does increasing the number of rope wind- ings make it easier for the student pulling 2. Tie one end of the rope to one broom the rope to move the handles together? handle, and pass it once around the other handle. 2. What forces do the two students holding the handles experience? 3. A third student should try to pull the handles together using the rope, while Extension the other two try to hold them apart. 3. Is there any change in how far the student has to pull the rope as the number of 4. Now wind the rope a couple more times windings increases? around the handles, and try again. The Wheel and Axle, Gears, and Pulleys MHR 293 S K I L L C H E C K Initiating and Planning Performing and Recording 4-C Analyzing and Interpreting Communication and Teamwork Pick It Up Imagine you and your group are a team of Safety Precautions engineers working for the Ace Crane Company. You are in the process of developing a new crane Materials wood, cardboard, dowelling, Lego™ parts (or similar to be used in the construction industry. construction kit parts), string, glue gun, 12 N weight Challenge Design Specifications Use your knowledge of simple machines to design Build a model (a prototype) that can lift a load of and build a prototype of a crane. The crane must 12 N (to represent the 12 000 N weight) with an feature a wheel-and-axle system that can lift effort of 4 N (to represent the 4000 N force). weights of up to 12 000 N. The motor that must be used to turn the crane’s wheel-and-axle system Plan and Construct can generate a force of 4000 N on the rim of As a group, discuss potential designs. Make the axle. technical drawings and discuss possible prob- lems with each design until you have decided on a design that you think will work. Select the materials for the prototype. Show your plan to your teacher for approval. Collect your materials and draw a blueprint. Assign the tasks among your team members. Construct your prototype. You should have some members of your team working on the wheel-and-axle system and others working on the body of the crane. Test your crane using a 12 N load. Evaluate 1. Does your mechanical device satisfy all the conditions in the Challenge? If not, how could you modify the design to make it work? If you have the opportunity, make and test your modiﬁcations. 2. Write a report that describes your device. Include your blueprint and clearly label each part. Discuss any problems your team had with the device and present possible solutions. 294 MHR Mechanical Systems TOPIC 2 Review 1. Draw a sketch of a single pulley in an arrangement that gives a mechanical advantage of 1. Then draw a sketch of a single pulley in an arrangement that gives a mechanical advantage of 2. 2. If you wanted a winch to have a mechanical advantage of 4 and the radius of the axle was 5 cm, how long would the handle have to be? 3. Find the overall mechanical advantage of the pulley system shown in the diagram below. 4. Thinking Critically If a bicycle has two sprockets on the front and four sprockets on the back, how many different gear combinations should it have? 5. Design Your Own Design an experiment that would test the advantage of using a mechanical system to lift a bucket of cement to a height of 1 m. Use the mechanical system of your choice (e.g., inclined plane, pulley, etc.). Be sure to identify responding and manipulated variables, and to specify a control. After you have performed your investigation, list criteria for assessing your solution to the problem. The Wheel and Axle, Gears, and Pulleys MHR 295 T O P I C 3 Energy, Friction, and Efficiency A Work and Energy You have learned about many different kinds of simple machines in the last two Topics. In every case — levers, pulleys, gears, and sprockets — when someone did work on the machine, the machine did work on a load. You have learned that, in science, work has a speciﬁc meaning. Have you ﬁgured out just what work really is? Work is a transfer of energy. You use energy when you push on the pedals of a bicycle and make them move (see Figure 4.25A). Now the pedals have the energy of motion called kinetic energy. The pedals are attached to the B sprocket. This combination forms a wheel-and-axle machine. This machine does work on the sprocket and chain machine, transferring energy to it. Trace the energy transfers throughout the entire bicycle. What is the ﬁnal form of energy? You may already know that energy cannot be created or destroyed. It has to come from somewhere. When you do work on a machine, where did you get the energy? Your energy came from the chemical energy C stored in the food you eat. Most of today’s machines are not “people powered.” Two of the most common sources of energy for machines are illustrated in Figure 4.25 B and C. Most vehicles such as this large combine obtain energy from fuels such as gasoline. The refrigerator runs on electrical energy. Stored Energy Energy must be transferred to a machine to make the machine work. However, we want to control when the machines work and when they Figure 4.25 (A) The source do not. So, we need to store the energy in some way, then use it when of energy for this machine we need it. Stored energy is also called potential energy. Much of the is the person. (B) This energy for machines, including your body, is stored as chemical energy. combine gets its energy You could call this chemical potential energy. from fuel. (C) Electricity is the source of energy In the next activity, you are going to transfer energy to a machine for the compressor on made of a tube and small ball. This activity will help you to understand this refrigerator. another form of potential energy, gravitational potential energy. You will do work on the ball by lifting it to a high level. When you lift it to a higher level, what is the form of the energy that you have transferred to the ball? It is not moving so it has no kinetic energy. However, if you released it, the force of gravity would make it fall and give it kinetic energy. This type of stored energy is called gravitational potential energy. What practical systems store energy in the form of gravitational potential energy? Hint: Look at Figure 4.26. 296 MHR Mechanical Systems The ultimate source of energy for Earth is the Sun. The Sun causes winds to blow, drives the water cycle, and can be captured as solar energy. As well, some fuels, such as oil and gas, are made of the remains of plants that grew million of years ago using the Sun’s ener- gy. Can you think of other Figure 4.26 How is gravitational potential energy being stored here? Into forms of energy and how what form of energy will this stored energy be converted? the Sun affects them? Find Out A Rubber Roller Coaster What is the best design for a roller coaster? Performing and Recording Your challenge is to work in a team to design a Procedure Communication and Teamwork roller coaster with two hills. A small ball must 1. Tape one end of the tube to the wall. Have be able to travel the entire length of the tube. one person in your team hold the other Materials end of the tube at chest height. 4 m of 5 mm diameter vinyl or rubber tubing 2. Use the rest of the tubing to make two tape hills. Determine the maximum height that small ball that will fit inside tubing the hills can be so that the ball still makes (for example, ball bearing) it to the end of the tube. metre stick 3. Examine the photograph. Will the students’ design work? Explain. Experiment with other designs. How do different designs affect the movement of the ball? Sketch some of your designs and describe how well they worked. What Did You Find Out? Analyzing and Interpre Sketch your roller coaster and show where the ball has potential energy and where it has kinetic energy. Energy, Friction, and Efﬁciency MHR 297 Energy Transmitters Earlier you learned how energy can be converted from one form into another. Energy, or power, can also be transmitted. In energy transmission, the energy is transferred from one place to another, and no energy is changed or converted. For example, the chain on your bicycle links the two sprockets. Electrical wires transmit the power from the generating station to your home. The chain and the electrical wires are both energy transmitters. Figure 4.27 The fan belt transmits power from a car’s crankshaft to a fan that cools the radiator and to a pulley that turns an alternator. The alternator produces electricity for use in the car or storage in the battery. No Machine Is 100 Percent Efficient An ideal machine would transfer all of the energy it received to a load or to another machine. However, real machines do not work this efﬁciently. Some of the energy is always lost. The work output of a machine is always less than the work input. No machine is perfect, but some machines come closer than others. The efficiency of a machine tells you how much of the energy you gave to the machine was transferred to the load by the machine. Efﬁciency is a comparison of the useful work provided by a machine or a system with the work supplied to the machine or system. Efﬁciency is usually stated as a percentage. If we use a lever as an example, you can calculate the efﬁciency of the lever by using this formula: Work done by lever on load Efficiency = × 100% Work done on lever by effort force The higher the efﬁciency, the better the lever is at transferring energy. A “perfect” machine would transfer all the work done by the effort and would be 100 percent efﬁcient. However, the efﬁciency of real machines is always less than 100 percent. Why? Every time a machine does work, some energy is lost because of friction. Think about a pair of hedge trimmers. As you close the handles, the blades rub against each other. If the blades are rusty, they will tend to stick even more. Many car engines are You could summarize this situation by means of the following only about 20 percent word equation: efficient. Where does all the “lost” energy go? Work done on a machine = Work done by the machine + energy lost as heat due to friction 298 MHR Mechanical Systems Many machines can be made more efﬁcient by reducing friction. You can usually do th

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