4 Pulleys and Gears I Plant Growth Magnetism Forces and Movement Stability Soil 4.. Habitats Light Sound Pulleys and Gears Rocks and Minerals The Human Body Changes in Matter Conservation of Energy Forces on Structures Weather Diversity of Living Things Air and Flight Electricity Motion Space ISBN 0-13-504550-9 Addison Wesley
Coordinating & Developmental Editors Jenny Armstrong Lee Geller Lynne Gulliver U n i t 4 Editors Susan Berg Jackie Dulson Christy Hayhoe Sarah Mawson Mary Reeve Keltie Thomas Researchers Paulee Kestin Louise MacKenzie Karen Taylor Wendy Yano, Colbome Communications Centre Reviewers Anita Hayhoe, Brampton Christian School, ACSI Lynn Lemieux, Sir Alexander MacKenzie Sr. P.S., Toronto District School Board Sidney McKay, Brookbanks Education Centre, Toronto District School Board Klaus Richter, formerly Edgewood P.S., Toronto District School Board In this unit, you will learn about two special kinds of wheels: pulleys and gears. Pulleys and gears play an important part in our lives. Even when we can't see them, they are in machines all around us. They help us to get where we're going (in bus and car engines, and bicycles). They keep us on time (in watches and clocks). They make tasks easier (in eggbeaters and cranes). They even allow us to skip the stairs once in a while (in escalators and elevators). Pearson Education Canada would like to thank the teachers and consultants who reviewed and field-tested this material. Design Pronk&Associates Copyright 2008 Pearson Education Canada Inc., Toronto, Ontario All rights reserved. This publication is protected by copyright, and permission should be obtained from the publisher prior to any prohibited reproduction, storage in a retrieval system, or transmission in any form or by any means, electronic, mechanical, photocopying, recording, or likewise. For information regarding permission, write to the Permissions Department. The information and activities presented in this book have been carefully edited and reviewed. However, the publisher shall not be liable for any damages resulting, in whole or part, from the reader's use of this material. Brand names that appear in photographs of products in this textbook are intended to provide students with a sense of the real-world applications of science and technology and are in no way intended to endorse specific products. ISBN 0-13-504550-9 Printed and bound in Canada. 1 2 3 - TCP - 10 09 08 Launch: Finding Pulleys and Gears..................... 2 1: Pulley Power 4 2: Using One Pulley 7 3: Using More Than One Pulley 10 4: How Pulleys Work 13 5: Gearing Up 16 6: Gearing Up Again 20 7: How Gears Work 23 8: Gears on the Bike Go Round and Round 27 9: The History of Bicycles 31 Design Project: Design a Crane 36 Unit Review 39 Glossary 43 Addison Wesley
1. In a small group, list all the examples of pulleys and gears that you see in the illustration. How are structures used to support the pulleys? 2. Look at the examples of pulleys you recorded. In what ways are they similar? For what types of tasks are pulleys often used? IEI SCIENCE & TECHNOLOGY 4 3. Now look at the examples of gears you recorded. How are they similar? How are they different? 4. What can pulleys do that gears can't do? Communicate \i ~ Discuss Write ~ 1. List and share any questions you have about pulleys and gears. 2. After school, go on a pulley and gear hunt in your own home or with a partner around. your neighbourhood. Describe all the examples of pulleys and gears you find. In some cases you might not be able to see the gear or pulley because it is inside a machine. As long as you know the machine contains a pulley or gear, you can include it in your list. Combine your list of examples with other students in your group. Share your combined list with the class. 1!!11!1 On What You Know Start a scrapbook. Begin by collecting pictures of pulleys and gears or machines that contain pulleys and gears from magazines, brochures, and on the Internet. Gradually, you will be adding more pictures and your own drawings to the scrapbook. At the end of the unit, take your scrapbook home to share with family members. PULLEYS AND GEARS Ill
1 Pulley Power " Work On It In this activity, you will learn about how pulleys work by designing and making a system that will lift an object off the floor. Safety Caution Be careful when handling sharp tools such as scissors and skewers. Materials for each group: string tape scissors paper clips medium-sized rock wooden dowel empty thread spools spring scale bamboo skewers ruler straws Procedure D Cut a piece of string about 1 m long. Make a loop on one end. Tie the other end of the string around the rock. fj Use the spring scale to lift the rock straight up. Record the number on the spring scale. This gives a measure of the force you had to use to lift the rock with your arm. You have seen some of the many ways that pulleys and gears are used in our lives. There are uses of pulleys you might not have discovered that may surprise you. The photograph shows how a pulley system in Niger, Africa is used to get water from a well. A wooden structure was built to support a pulley. One end of a rope is passed over the pulley and attached to an animal-hide bucket. By attaching the other end of the rope to a donkey, the bucket can be raised and lowered. This piece of equipment doesn't work by itself. Someone or something has to pull the rope to start the motion of raising or lowering the bucket. All motion is caused by a force. A force is a push or pum The effort needed to pull on a rope or lift an object is an example of a force. Ill SCIENCE & TECHNOLOGY 4 I., T I.I I I..A.. PULLEYS AND GEARS D
IJ Look at the materials that you have. With your group, brainstorm ways you could use the materials to build a mechanical system that will lift the rock off the floor. Include a pulley in your design. I] Select the best idea from the ideas your group brainstormed. Write a brief description of the system. Explain how you think it will work m Build your system and use it to lift the rock Using a spring scale, measure and record the force needed to lift the rock Notice the direction of the force. m Change your system or select another idea to test. Record your new idea and build the new system. Using a spring scale, measure and record the force needed to lift the rock Did it take less force to lift the rock than it did with the first system? Was the force in the same direction? Communicate Write Discuss Present 1. What mechanical systems did you create to lift the rock? 2. Which system required the least effort to lift the rock? Draw a picture of it. Why did this system work best? How did the structure help with the task? 3. Did your system allow you to change the direction of the force by pulling down on the pulley rope? Explain how this is helpful in lifting a load. 4. Present and compare the results of your investigation with those of other groups. How were the systems you developed different from theirs? How were they the same? 5. If you were to try this activity again, what changes would you make to your mechanical system to improve the way it lifted a load? Explain. 2 Using One Pulley You have investigated. what a pulley is, how it works within a structure, and the different ways that spools and string can be put together to form a pulley system. You may have discovered. that some pulley systems can reduce the force needed to lift an object. Others can only change the direction of the force. They let you pull down on the pulley rope rather than lifting up. In this activity, you will compare the ways that a single pulley can be used to lift a load.,... On v,,j. In Pulley Power, you used thread spools, string, and bamboo skewers to build a pulley system. These materials were not made for this use. Because of this, there is a lot of friction between the spool and the skewer, and between the spool and the string. Friction is a force that slows down motion. It occurs when two objects rub together. Because friction works against movement, it increases the amount of force you have to use to get the pulley to work In this activity, you will use commercial pulleys, which create less friction than the pulleys you have created. Fixed Pulley System In this activity, you'll be using a fixed pulley system to lift a load. In a fixed pulley system, the pulley is attached to a structure and does not move. Materials for each group: pulley string spring scale ruler metre stick 2 chairs load - a 200 g mass, or a book SCIENCE & TECHNOLOGY 4 ------ PULLEYS AND GEARS
Procedure O Cut a piece of string and tie it to the load. Attach the spring scale and pull up to measure the force needed to lift the load straight up with your arm. Record the force. fj Use another piece of string to tie the pulley to the metre stick Make sure the pulley can turn easily. Balance the metre stick over the backs of two chairs to keep the pulley firmly in place. fj Attach the load to the pulley. 2. With a fixed pulley, how is the direction of the force needed to lift the load different than without the pulley? 3. With a movable pulley, does it take less force to lift the load than with the fixed pulley? 4. With a movable pulley, how is the direction of the force needed to lift the load different than without the pulley? 5. When would you use a fixed pulley to lift a heavy object? When would you use a movable pulley to lift a heavy object? m Remove the load and untie the pulley from the metre stick Keep your materials for use in the next part of this activity. Movable Pulley System In this activity, you'll be lifting a load using a movable pulley system. In a movable pulley system, the pulley supports the load and is not fixed in place. II With a smooth motion, lift the load by pulling up on the spring scale. 6. Compare the commercial pulleys you used in this activity with the "homemade" pulleys used in Pulley Power. Which materials would you rather work with? Why? 7. Look back at the list of pulleys you observed in Finding Pulleys and Gears on pages 2 and 3. Which pulley systems do you think are fixed and which are movable? Which type of pulley is more common? Did you find any pulley system that was different from the two you investigated in this activity? II Place a 1 m piece of string in the pulley groove. Tie a loop at one end of the string. I) Tie one end of the string around the load and connect the looped end to the spring scale. Lift the load by pulling down on the spring scale with a smooth motion. m How much force do you need to lift the load? Were you pulling in the same direction as when you lifted the load in step l? Materials for each group: Use the materials from the Fixed Pulley System activity Procedure Tie one end of the string that passes through the pulley groove to the metre stick Balance the metre stick over the backs of two chairs. Connect the other end of the string to the spring scale. I) How much force do you need to lift the load this time? Were you pulling in the same direction as when you lifted the load without a pulley? Communicate Write 1. With a fixed pulley, does it take less force to lift the load with the pulley or without a pulley? 8. Look at the structures that hold the pulleys in the illustration on pages 2 and 3. What role does the structure play in these pulley systems? Try to find a picture of a machine with a single fixed pulley and one with a single movable pulley. Or, draw a picture of each type of pulley. Add these pictures to your scrapbook, and for each picture, write a brief description of how the pulley works. SCIENCE & TECHNOLOGY 4 PULLEYS AND GEARS D
3 Using More Than One Pulley Can you imagine a pulley system that involves both a fixed pulley and a movable pulley? What about a system that has two fixed pulleys and one movable pulley, or one fixed pulley and two movable pulleys? How would these systems work? In this activity, you'll get a chance to find out. Materials for each group: single pulleys double pulleys triple pulleys string spring scale ruler metre stick 2 chairs load - 200 g mass, or a book Procedure D With your group, plan an investigation to determine how well different pulley systems work to raise a load. Make sure your investigation is a fair test. To ensure it is a fair test, you must keep all the conditions of the investigation the same except for the variable you are testing. Variables include the size of the load and the number of pulleys. How will you make sure your test is fair? fj Look at the materials you have. With your group, brainstorm ways to use these materials to lift the load off the floor using the least force. As you brainstorm, think about the differences between fixed and movable pulleys. IJ Design several systems that combine both types of pulleys in different ways. Then choose one system that you think will lift the load with the least force. Why do you think it will lift the load using the least force? I) Write a detailed description of what your system looks like and how it works. How will you attach the pulleys to a structure so they are stable? ~tarted You now know what a pulley is and how it works. You have used both fixed and movable pulleys. You compared the pulley systems you have built to those you have seen around you. Did you notice that machines often link several pulleys together? In this activity I you'll investigate combined pulley systems (sometimes called block and tackle). Commercial pulleys are available that have two or three wheels joined together. Some are joined with one pulley in front of the other, while others are joined with one pulley above the other. If they are available, you will use double and triple pulleys in this activity. You can use as many or as few of the wheels on each pulley as you wish.
m Build your system and use it to lift the load 10 cm above the floor. Measure and record the force needed to lift the load. Communicate Write 1 Discuss ~ 1. Share your investigation and results with another group. Explain your experiment and answer any questions your classmates have. Look at your classmates' investigation. How did they make sure that their investigation was a fair test? 4 How Pulleys Work.. 2. How do the results of your investigation help you to understand how well different pulley systems move a load? Why did some systems work better than others? 3. What happens to the force needed to lift the load when you use more than one pulley? Explain. In your investigations so far, you have discovered that pulleys can be used to reduce the force needed to lift a load. Now it's time to learn more about how pulleys work. As you read through this information, 4. What happened to the direction of the pull when you used more than one pulley? keep a list of any words that are new to you. m Select another system to test. Record your idea and build your new system. Did it need more or less force than the first system to lift the load? 5. Which arrangement of pulleys used the least force to lift the load with your pulling down? 6. Which arrangement used the least force with your pulling up? 7. Describe any place or places where you have seen two pulley systems used together. I;$ n I On What You Know You've learned that the effort needed to lift an object is an example of a force. Gravity is also a force. It acts on all objects on Earth-including you-attracting them toward the ground. Gravity keeps you from floating into space! >SSS-... I.. Find a picture of a machine that uses more than one pulley. Or, invent a machine of your own with several pulleys and draw a picture of it. Add the picture to your scrapbook. Describe how the machine is used. The weight of an object is a measure of the force of gravity acting on it. This is called the load force. In order to lift an object, you must work against the force of gravity. This is called the effort force. The comparison of the load force to the effort force needed to lift the load is called the mechanical advantage. A fixed pulley can help you lift a load by allowing you to pull down on a rope. Pulling down is easier than lifting up a load by yourself. Imagine you had to move a refrigerator to the third floor of a building. Using a pulley to lift the refrigerator is much easier than carrying it up three flights of stairs! '
FIXED PULLEY With a fixed pulley, when you pull down on the pulley rope, the load moves up. A fixed pulley changes the direction of the effort force. This means that you can use your whole body to pull down to lift the load. With only one pulley, however, the effort force is equal to the weight or load force of the object. Effort Force l Load Motion Poree A single fixed pulley changes the direction of the effort force. But you must use the same amount of effort force to pull as you would if you were lifting the load without a pulley. COMBINED PULLEY A combined pulley system uses both a fixed pulley and a movable pulley. The fixed pulley in this system changes the direction of the effort force. This allows you to pull down to lift the load. The movable pulley in the system lets you pull using only half the effort force. This is because the pulley rope takes half the weight of the load. l Load Force Motion A combined pulley system has the benefits of both a fixed and a movable pulley-you pull down and use only half the effort force you would need to lift the load without a pulley. Effort Force Motion A single movable pulley does not change the direction of the effort force. But you need to pull with only half the effort force you would use with a fixed pulley or with no pulley at all. i Load Force,I L. With a single movable pulley, the pulley is attached to the load and the rope is attached to the ceiling. To lift the load, you pull up on the other end of the rope. So, the effort force is in the opposite direction to the load force. The benefit of a movable pulley is that you only have to pull with half the effort force to lift the load. This is because the rope attached to the ceiling takes half the weight of the load. A pulley system makes it easier to lift a load because it can a. change the direction of the force needed to pull (fixed pulley) b. reduce the force needed to pull (movable pulley) c. change the direction of the force needed to pull and reduce the force needed to pull ( combined pulley) Communicate Write 1. What is the advantage of a single fixed pulley system? 2. What is the advantage of a movable pulley system? 3. What is the disadvantage of a movable pulley system? 4. Look at the picture of the combined pulley system. What type of pulley is the upper pulley? The lower pulley? 5. What are the two advantages of a combined pulley system?
~ 5 J Gearing Up Up to now, you have used pulleys to transfer movement. Another way to transfer movement is to use gears. Gears have interlocking teeth that connect with and move each other. How does the number of teeth on a gear system affect the speed and direction of its motion? Investigate gears in this activity to find out. Safety Caution Materials for each group: 2 corrugated cardboard sheets scissors finishing nails safety goggles Always wear your safety goggles when working with sharp objects such as nails. Trace theses gears to make your own... PULLEYS AND GEARS ID
Procedure D Trace each of the gears shown onto separate pieces of paper. Cut out each gear and trace around or glue them onto one of the cardboard sheets. Mark the centres, then carefully cut out the gears to make two small gears, one medium gear, and one large gear. Colour one tooth on each gear to help you count the number of times the gear turns. lr:i Wearing your safety goggles, push a nail U through the centre of each gear. Use the nail to attach one small gear to one of the cardboard sheets. Pin the second small gear next to it so that the teeth interlock. IJ Turn the first gear. What happens to the second gear? What direction does it turn? If you turn the first gear one full turn, how far does the second gear turn? How can you tell? Use a chart like the one shown to help organize your observations. 1st Gear Drscnon I Number I :2nd 1t turns of turns gear m Drecnon I Number 1t turns of turns Replace the medium gear with the large gear. Pin the large gear in place so that the teeth interlock with the small gear. a. Turn the small gear. What happens to the large gear? What direction does it turn? b. If you turn the small gear six full turns, how many times does the large gear turn? How can you tell? Communicate. i... Discuss Write small small 1. What do you notice about the direction of small medium movement of each pair of gears? small large I) Replace the second small gear with the medium gear. Pin the medium gear in place so that the teeth interlock with the small gear. Turn the small gear. a. What happens to the medium gear? What direction does it turn? b. If you turn the small gear six full turns, how many times does the medium gear turn? How can you tell? fj Suppose you were to turn the large gear. For each full turn, predict if the small gear will turn more than one, less than one, or exactly one full turn. Use the materials to check your prediction. Tum the large gear twice. How many times does the small gear turn? m Experiment with other gear combinations and with three gears connected together. What conclusion can you make? Save your gears for use in the next activity. 2. Count the number of teeth on each gear. How does the number of teeth on each gear affect the number of turns you get with different pairs of gears? 3. Suppose the first gear in a system has ten teeth. How many teeth should the second gear have if you want to get one turn from it for every three turns of the first gear? Explain. 4. Where might gears be used? I :mj n I On What You Know I Find photographs of real-life machines that use gears. Or, design your own imaginary machine with gears and draw a picture of it. Add the photographs or drawing to your pulleys and gears scrapbook. Include as much information as you can about what the machine is used for and how it works. m Suppose you were to turn the medium gear. For each full turn, predict if the small gear will turn more than one, less than one, or exactly one full turn. Use the materials to check your prediction. Turn the medium gear four times. How many times does the small gear tum?
6 Gearing Up Again In this activity, you'll investigate whether the cardboard gears you created in the last activity will work if they meet at an angle. How will motion be transferred? Will the same relationships hold between the number of teeth on each gear and the number of turns? Materials for each group: cardboard gears from Gearing Up corrugated cardboard sheet finishing nails safety goggles Optional Materials: thin cardboard sheet Safety Caution Be very careful when handling sharp objects. Remember to protect your eyes! Procedure D Wearing your safety goggles, push one nail through the centre of each gear. fj Fold the corrugated cardboard sheet in the middle and hold it as shown below. Pin one small gear onto the vertical part of the cardboard near the bottom. Pin the other small gear onto the horizontal part of the cardboard. The teeth of both gears should interlock. Water wheel Started The gears you have investigated work on a flat or horizontal surface. They are called spur gears. Sometimes, machines contain gears that meet at an angle. If the first gear is vertical (upright) and the second is horizontal, we say the gears meet at a right angle. The vertical motion of the first gear is changed to the horizontal motion of the second. Gears that meet on an angle are called bevel gears. In old-fashioned mills, systems of gears were used to change the vertical motion of a waterwheel to the horizontal motion of millstones for grinding grain. Falling water was used to turn a large wheel. As this wheel's axle (a bar or rod connected to the wheel) turned, it set in motion a series of gears and pulleys. In some mills, these included bevel gears as shown above.
7 I How Gears Work IJ Tum the vertical gear. a. What happens to the horizontal gear? b. If the vertical gear is turning clockwise, in which direction does the horizontal gear turn? c. For each full turn of the vertical gear, how many turns does the horizontal gear make? If Time Allows Replace the corrugated cardboard gears with similar gears made of thin cardboard. Predict how this gear system will work compared to the previous system. Will thinner, more flexible gears work as well as sturdy, thick gears? Check your prediction. Communicate '"' "' Write Discuss Discuss these questions with a partner. 1. What is special about this type of gear system? When might it be used? 2. Draw a picture of a gear system that would change the direction of motion from vertical to horizontal, and for which every turn of the vertical gear would result in two turns of the horizontal gear. 3. What effect do different materials have on gear operation? Why do you think gears are usually made of metal? What would happen if gears had to be made of other materials, such as wood? Remember, you can recycle your card.board when you are finished with it. Research to find examples of real-life machines that use pulley and gear systems together. Draw the machines. Or, design and draw your own imaginary machine that uses pulleys and gears. Describe how the turning motion of one system is transferred to a turning motion in the other system. Add the drawing and description to your scrapbook. J I _) ] l J [- ~ $tarted You have already learned a lot about gears. Like pulleys, gears can be used to transfer forces and motion from one object to another. Some gear systems, like the ones you've worked with, can also be used to change the direction of the motion. As you read, create a mind map of terms related to gears. Most gears are flat wheels with teeth around their edges or grooves along their sides. Some gears have other shapes, like cylinders and cones, with teeth or grooves cut into them. Gears are usually attached to axles or shafts and are used to transfer circular motion from one shaft to another within a machine. In doing this, gears can change the direction of the force. They may also change the strength of the force.
When two interlocking gears have the same number of teeth, they turn at the same speed, but in opposite directions. When two gears have different numbers of teeth, they turn at different speeds. If a small gear turns a large gear, the small gear must turn more than once to cause the large gear to complete one turn. So, the large gear turns more slowly than the small gear. In this way, gears can be used to change the speed of motion. What do you think would happen to the small gear if the large gear is turned? If the large gear is turned, the small gear turns in the opposite direction and at a faster speed! In Gearing Up, you created spur gears. In spur gears, the teeth meet on a flat surface and can change the speed and direction of motion. Spur gears are used in car transmissions. Two equal-sized gears In Gearing Up Again, you created a form of bevel gear. Your bevel gears were flat wheels, but bevel gears are often cone-shaped. In bevel gears, two gears connect at an angle. They can also change the speed and direction of the motion. To keep the direction of the motion the same, you need to use three gears. In a three-gear system, the second gear changes the direction of the motion. The third gear changes the direction of that motion again, and moves in the same direction as the first gear. When you put many gears together it is called a gear train. Two different-sized gears There are many types of gears designed for different purposes. They differ in the arrangement and type of teeth, the way the axles are put together, and the angle at which the teeth meet. In worm gears, an axle or shaft has a screw thread that connects with another gear. This system is often used to reduce the speed and change the direction of the motion. Bevel gears are used in egg beaters. Three equal-sized gears Worm gears are used in electric mixers.
In rack and pinion gears, a single gear, called the pinion, meets with a toothed rack. The rack may slide or stay in one place. The system changes circular motion into motion in a straight line. When railroads are built on very steep hills, they may use rack and pinion gears to help keep the train on the tracks. 8 Gears on the Bike Go Round and Round Rack and pinion gears are used in a cogwheel railway. Communicate Write 1. When two gears connect, in what direction does each gear turn compared to the other? 2. If three gears are connected in a gear train, in what direction does each gear turn compared to the others? 5. Imagine you want to turn a crank that is very difficult to turn. You can use a small and a large gear to connect the crank to the handle that you turn. Does the small gear go on the crank axle or on the handle you turn? Does the large gear go on the crank axle or the handle? 3. Describe how gears operate when they connect on a flat surface and when they connect on an angle. 4. Look around your school, home, and community for examples of each kind of gear system-spur gears, bevel gears, worm gears, and rack and pinion gears. a. Which gear system appears to be most common? Give a reason why. b. Were gear systems easy or difficult to find? Explain. In your scrapbook on pulleys and gears, try to describe a machine that uses each of the gear systems described. Make a sketch of each machine and note the type of gear it uses. L Started So far, you've investigated gears and how they work, and you have looked for machines that use gears. There is one machine with gears that you may know well-a bicycle. Bicycles have sprocket and chain gears that work like some pulley systems. A chain connects the sprocket gears on the pedals to the back wheel. The chain also allows the gears to turn in the same direction. The sprockets keep the chain from slipping as it turns. What do gears do for a bicycle and for a bicycle rider? To find out, you'll be looking more closely at the gears on a bicycle.
Number of Number of Number of Number of gear teeth on gear teeth on pedal turns back wheel front sprocket back sprocket turns Low gear 1 High gear 1 I I) When the chain passes around a large back sprocket, the bicycle is said to be in low gear. Put the bicycle in a low gear. Count the number of gear teeth on the front and back sprockets that you are using. Record your observations in a table like the one shown above. m When the chain passes around a small back sprocket, the bicycle is said to be in high gear. Put the bicycle in a high gear. Again, count the number of gear teeth on the front and back sprockets that you are using. Record your observations in a table like the one shown above.. ork On For this activity, you'll need to use a bicycle that has different gears. These are sometimes called 3-speed, 5-speed, and so on, depending on the number of gear combinations they have. Materials for each group: bicycle with gears tape paper scrap piece of wood Procedure D Turn the bicycle upside-down so that it rests on its handle bars and seat. Tape a small piece of white paper on the back tire as a marker. fj The gears on a bicycle are called sprockets. Look at the back sprockets. How many are there? How are these sprockets similar to each other? How are they different? Low gear II Use a scap piece of wood to apply friction to the back wheel. Turn the pedal one complete turn while you observe the back wheel. What happens? m Notice the force needed to turn the pedal in order to get the back wheel turning in low gear. Safety Caution Turn the pedal slowly and keep your fingers away from the wheel spokes. High gear IJ Repeat step 4. How many turns does the back wheel make in one complete pedal turn? Record your observations in the table. m Notice the force needed to turn the pedal to get the back wheel turning in high gear. How does this force compare to the force needed in low gear?
Communicate Discuss Write... Discuss the following questions with your group. 1. Why do you think there are different sprockets attached to the pedals, and other sprockets attached to the back wheel? 2. Which gear is best for going up a steep hill? Why? 3. Which gear is best for travelling the fastest on flat ground? Why? 4. Why aren't the gears and chain painted? Explain. 5. What material is put on the gears and chain of a bicycle to make them work better? 6. Look at another mechanism on the bicycle-the brakes. Describe what happens when you squeeze the brakes. How do they work to slow down the bicycle? 7. Can you find any examples of pulleys on the bicycle? 8. How does the structure of a bicycle allow mechanical systems such as gears to work? Make a sketch to show how the gears and chain of a bicycle look in low and high gear. Explain how the number of teeth on the sprockets affects the turning of the wheels and the bicycle's motion. Add your sketch and information to your scrapbook. 9 The History of Bicycles Started ~~ In the last activity I you learned that the way a bicycle1s sprocket and chain gear system works depends on the size and number of teeth of the two sprockets in use. You know that in any pair of wheels joined by a belt or chcdn, the larger wheel will rotate more slowly than the smaller wheel. The bigger the difference in size between the two wheels, the bigger the difference in speed. The gear shifter of a bicycle allows the rider to change the sizes of the sprockets being used. In low gears, the back sprocket is large. This means that the back tire will rotate fewer times for one pedal turn when compared to higher gears. But, you need less force to make the pedal turn. This is useful for climbing hills. In high gears, the back sprocket is small. The back tire will rotate more times for one pedal turn when compared to lower gears. This means the bicycle travels farther with each pedal turn, which allows you to go faster on level ground. But, you must use more force to make the pedal turn. Today, we take it for granted that a bicycle has a chain, pedals, gears, brakes, and rubber tires. But the earliest bicycles lacked most of these items. When were bicycles first developed? How have they changed over the
years? What might the bicycles of the future look like? As you read through this information about bicycles of the past, present, and future, work with a partner to develop a timeline of the history of the bicycle. At each stage of the timeline, record what you think are the most important features of the bicycle. The first known bicycle, called the Draisienne, was built and used in Paris in 1817 by Baron von Drais. But it was very different than today's bicycle. It had two wheels of equal size that could turn but the bicycle always faced straight ahead. Between the wheels was a frame on which the rider sat. This bicycle was made entirely of wood. The rider made the bicycle move by pushing his feet along the ground. In the second version of this bicycle, von Drais changed the design so that the front wheel could be turned to the left or right to steer the bicycle. The next major innovation occurred in 1865 when a machine known as the Velocipede became popular. It was invented in 1861 by two Frenchmen named Pierre Michaux and his son Ernest. The rider used his feet to turn pedals attached to the machine's large front wheel. The first models of the Velocipede were made of wood, but later models had metal tires. They were heavy, difficult to steer, and could reach only limited speeds. Despite this, they became popular. In large cities, indoor riding rinks were set up. Models were even developed that could be used on ice! The name Velocipede means "fast foot". The machine was also known as the "bone shaker" because of the discomfort of riding it on bumpy cobblestone roads. By the 1870s, the first all metal machines with solid rubber tires were produced. Their design resembled the Velocipede. They were the first machines to be called bicycles. The word bicycle means "two wheels." Later models of the bicycle such as the "penny-farthing", created by James Starley in 1870, were made with a large front wheel and a small back wheel. The larger the front wheel, the farther the bicycle travelled with every turn of the pedal. This meant that the rider did not have to pedal so fast to keep moving. However, these bicycles could be dangerous as they tipped easily when riding over uneven road surfaces. For a time in the late 1800s, adult-sized tricycles were popular. These tricycles could also be used by women, whose long skirts made it difficult to ride the high wheelers. Many of the mechanical systems invented for these tricycles were later used by the automotive industry. Two examples are hand brakes and the rack and pinion steering systems. This tricycle from 1882 is called the Royal Salvo. Unlike the high wheelers, the tricycle's pedals were not attached directly to the wheel. The Draisienne, or "swift-walker" as it was also known, was practical only for use on well-maintained pathways. The penny-farthing was also known as the "high wheeler" because of its large front wheel. By the 1890s, air-filled tires and a sprocket and chain gear system were introduced. The air-filled tires made the ride comfortable. The gears allowed people to travel as far with each pedal turn as with the high-wheeled bicycles, but without the need for a giant wheel.
Bicycles looked much as they do today, with equal-sized wheels and a metal frame. They were more comfortable and safer than ever before. The bicycle was on its way to being used widely around the world. Canada's first "homegrown" wide-tire mountain bike was created by Vancouver's Rocky Mountain Bicycles Ltd. in 1982. The RM9, shown, is their latest downhill race weapon. This circa 1896 advertisement from Massey-Harris shows the variety of bicycle styles available. Bicycles are now one of the world's most popular forms of transportation. Today, there are about 800 million bicycles in the world. This is twice the number of cars. The number of bicycles made every year is about three times the number of cars made. Many specialty bicycles have been built, such as mountain bikes, BMX bikes, freestyle bikes, racing bikes, touring bikes, and tandem bikes (bicycles for two riders). Two unusual types of modern bicycles are recumbent bicycles, which allow the rider to sit back, and Para-cycles TM. To drive a recumbent bicycle, you sit lower down, in a more comfortable position, with a backrest behind you. The pedals are in front of the wheels rather than between them. The Para-cycle TM is modelled on a recumbent bicycle frame but it has three wheels. It can be driven on the road like a bicycle, but can also fly in the air like a powered parachute! For take-off, it can climb at a rate of 150 m each minute with an 80 kg pilot. Are these examples of the bicycles of the future? Communicate 1 ~}. Write Discuss Discuss the following questions with your partner. l. What were the results of having a limited choice of materials when building early bicycles, for example, using metal tires instead of rubber, and using wood or metal frames instead of the light steel frames used today? The Para-cylce has an engine, removable power pack, and lifting parachute. 2. Which of the developments on your timeline did the most to make bicycles a practical and popular form of transportation? Why? Were you able to convince your partner of your choice? 3. a. List some of the advantages of bicycles over cars. b, List some factors that limit the use of bicycles. Can you think of ways to overcome any of these factors? Recumbent bicycles hold many speed records, although they are usually banned from racing. 4. Study the way your city or town is laid out. What would you change if you wanted to encourage more people to use bicycles as their main type of transportation? Design a new bicycle. How would you modify current bicycles to make one that is better or more fun to ride? What new parts would you add? Create a poster to advertise your new bicycle and explain its special features. Add this poster to your scrapbook. Take your scrapbook home and share it with family members to demonstrate what you have learned about pulleys and gears. Try to make your lists as complete as possible.
Design Project The pulley and gear systems you decide to build for your crane can be similar to the ones you have studied, or they can be new systems that you make just for this project. Look at the cranes shown, and at toy cranes if they are available, to get an idea of how cranes work As you work on your crane design, consider the following questions. What are the main parts of a crane? What types of movements do they make? How might you recreate these movements in a model crane? How do gears and pulleys help cranes work? Think about what materials you might use to build a working model. To help get you started, some possible materials are listed. You don't have to limit yourself to these suggestions! Materials for each group: pictures of cranes and toy cranes for reference pencils paper a variety of building materials such as plastic straws, boxes, craft sticks, paper fasteners, string, wire, cardboard, bamboo skewers, empty thread spools, wooden blocks, cardboard rolls from paper towels and toilet paper, glue, tape, scissors ~- it - -...-. - ~ ~-~.. -_. ~ ~ ~~- -~ ---~ s
Design Project Procedure D Brainstorm ideas with your group for the kind of crane you want to build. You could copy a crane you've seen, modify a crane you've seen so that it will work differently, or design a new one. Choose the best idea from your list. fj Once you have decided on an idea, make a detailed drawing of your crane. Describe what tasks your crane can be used for and how it works. Be sure to explain how the pulleys and gears help it to work Think about how you might create these parts and movements in a model. ij Decide what materials you will need. Work together to gather the materials and build your model crane. You may need to make changes to your design if you can't find some of the materials you need. I) Once you have finished your model, test it. Can it complete the tasks you intended? If not, try to think of ways to improve the crane. g Make a detailed drawing of your finished crane. Communicate Present Write Discuss 1. Present your group's crane to the class. Share your design sketches, demonstrate the tasks your crane can perform, and explain how the pulleys and gears help it to complete these tasks. 2. As you watched the presentations of other groups, you may have thought of ways to modify your own crane. What would you change about your crane if you were to build another model? Explain why you would make these changes. 3. Machines, such as cranes, that help people do work may damage the environment. In what ways might a crane change or harm the environment? 4. Discuss with your classmates the kinds of materials you would probably use if you were to make a real crane. How would the materials that were available affect the crane's use? For example, what would happen if you had to use wooden pulleys instead of metal ones? Demonstrate What You Know Get Started Now it's time to show how much you have learned about pulleys and gears. Read over what your tasks ere, and talk to your teacher if you are unclear about what to do. Work On It 1. Sarita and Catherine share a tree house in Sarita's backyard. To reach the tree house, they climb a rope ladder. They want to bring Catherine's pet dog into the tree house but the dog cannot climb the rope ladder. Neither girl can climb the ladder while carrying the dog. They decide to make a mechanical system that would use pulleys and/or gears to lift objects up to their tree house. 2. Sketch a design for the mechanical system, clearly label all the parts, and list the materials you would use to build it. 3. Write a description explaining how the system uses pulleys and/or gears to lift objects up into the tree house. 4. Now check your work My design uses a system of pulleys and/or gears to lift objects. My design has a labelled sketch, and a materials list. My description clearly explains how my design works. ~ My design and description show how pulleys and/or gears can be used to move objects.
~ -~ _i.t.. ~-... ;-:.-.. ~-. :;: l~review; _----------J------------------, Communicate Now it's time to think about how well you did. Use this chart to help you score your work Four stars is the highest score for each. 1 Star }r 2 Stars )< /( 3 Stars \ \ \ /( /( /( How much do you know about pulleys and gears? Look at your labelled sketch, list of materials, and description. Does your work show you know A little about Some A lot of pulleys and gears information information about pulleys and about pulleys and gears gears 4 Stars \ \ \ \,r( /(.:.: All about pulleys and gears? Look at the description of how your design works. Does your work show you have applied A few of the skills Some of the skills Most of the skills All of the skills to to use pulleys and/or gears to lift objects to use pulleys and/or gears to lift objects to use pulleys and/or gears to lift objects use pulleys and/or gears to lift objects? Now look again at your description. Will a reader find your description Not very clear Somewhat clear Mostly clear or precise and precise and precise Very clear and precise? How much understanding does your design show you have of how pulleys and gears can be used to move objects? Not much understanding Some understanding A good understanding A complete understanding Explain Your Stuff What did you learn about pulleys and gears? 1. a. Give two examples where a pulley system is used in everyday life. b. Give two examples where a gear system is used in everyday life. 2. Use a sketch to help describe an example of each of the following systems. Include an explanation of the forces and motion in the system. a. fixed pulley system b. movable pulley system c. combined pulley system (block and tackle) 3. Would you use a fixed pulley or a movable pulley to lift a heavy load of roofing materials to the roof of a building? Explain. 4. a. You have a system of two interlocking gears. If you turn one gear in a clockwise direction, what will happen to the other gear? b. You have five gears connected in a gear train. If you turn the first gear in a clockwise direction, in what direction will the last gear turn? 5. The first gear in a gear system has 12 teeth. a. Describe the gear you would use with it, if you wanted the second gear to turn three times as fast as the first gear. b. Describe the gear you would use with it, if you wanted the second gear to turn half as fast as the first gear. 6. Explain the difference between a high gear and a low gear on a bicycle. What is the advantage of each gear? 7. If you could investigate one question about pulleys and gears, what would it be? How would you investigate it? Write a short note explaining how well you think you did.
t How Did You Do? 1. List three things that you didn't know before completing this unit. 2. What activity did you like the best in this unit? Why? Which was your least favourite activity? Why? 3. Give yourself three compliments about the way you participated in this unit on pulleys and gears. What did you do well? 4. List three questions that you would like to answer the next time you study pulleys and gears. Now you know a lot about pulleys and gears! Here are some things you've learned: Pulleys and gears can be used alone or in combination in machines that make our lives easier. Pulley systems and gear systems can be modified to improve the way they move a load. A fixed pulley changes the direction of the effort force used to lift a load. A movable pulley reduces the amount of effort force needed to lift a load. But it does not change the direction of the effort force. When fixed and movable pulleys are used in combination, they change the direction of the effort force and reduce the amount of effort force needed to lift a load. When two interlocking gears have the same number of teeth, they turn at the same speed but in opposite directions. When two interlocking gears have different numbers of teeth, they turn at \ different speeds. The gear with more teeth turns slower. Multi-speed bicycles have sprocket and chain gears. In high gear, each turn of the pedals causes the bicycle to move farther than in low gear. However, it takes more effort to pedal in high gear. There are many mechanical systems on a bicycle that help it work. These have changed greatly since the first bicycles were produced to make today's bicycles more efficient. '1 Glossary I axle a bar or rod connected to the centre of a wheel bevel gears gears that meet at an angle; they can change the speed and direction of motion block and tackle a combined pulley system used to lift heavy objects; changes the direction of the effort force and reduces the amount of effort force needed to pull to lift a load cone an object shaped like a funnel without the tube; it has a circular base and curved surface that comes to a point cyllnder an object shaped like a can; two circular ends joined by a curved surface effort force the force required to work against the force of gravity to lift a load fixed pulley the pulley is attached to a structure and does not move; changes the direction of the effort force used to lift a load force a push or a pull friction a force, caused by objects rubbing together, that slows moving objects gear a wheel with teeth around its edge that interlocks with the teeth of other gears horizontal flat; parallel to the ground; straight across load force the weight of an object low gear when the chain on a bicycle passes around a large back sprocket movable pulley the pulley supports the load and is not fixed in place; reduces the amount of effort force needed to pull to lift a load mechanical advantage the comparison of the load force to the effort force needed to lift an object pulley wheel with a grooved rim and a rope, belt, or chain that passes around it rack and pinion gears a gear system in which a single gear (the pinion) meets with a toothed rack, which slides or stays in one place; changes circular motion into motion in a straight line sprockets the gears on a bicycle sprocket and chain a gear system in which a chain connects the gears to transfer motion (as on a bicycle) spur gears gears that meet on a flat or horizontal surface; can change the speed and direction of motion vertical upright gear train a group of two or more gears working together gravity the force attracting all objects on Earth toward the ground worm gears gears in which an axle or shaft has a screw thread that connects with another gear; the system changes the speed and direction of the motion high gear when the chain on a bicycle passes around a small back sprocket GLOSSARY m
Acknowledgments The publisher wishes to thank the following sources for photographs, illustrations, articles, and other materials used in this book Care has been taken to determine and locate ownership of copyrighted material used in this text. We will gladly receive information enabling us to rectify any errors or omissions in credits. Photography p. 1 (centre) Corbis/Richard Fukuhara, p. 1 (bottom) Chris Malazdrewicz/Valan Photos, p. 4 Corbis/Yann Arthus-Bertrand, p. 5 Ray Boudreau, p. 6 Ray Boudreau, p. 7 Ray Boudreau, p. 8 Ray Boudreau, p. 9 Ray Boudreau, p. 10 PhotoDisc, Inc., p. 11 Ray Boudreau, p. 12 Ray Boudreau, p. 16 Arthur Strange/Valan Photos, p. 18 Ray Boudreau, p. 19 Ray Boudreau, p. 20 (left) Jeff Greenberg/Visuals Unlimited, p. 20 (right) Deneve Feigh Bunde/Visuals Unlimited, p. 21 Ray Boudreau, p. 22 Ray Boudreau, p. 23 Alan Marsh/First Light, p. 25 (top) CP Picture Archive, p. 25 (centre) Ray Boudreau, p. 25 (bottom) Ray Boudreau, p. 26 R. D. Stevens/Valan Photos, p. 27 Corbis/Warren Morgan, p. 28 Ray Boudreau, p. 29 Ray Boudreau, p. 30 PhotoDisc, Inc., p. 32 Corbis/Gianni Dagli Orti, p. 33 (top and right) National Museum of Science' Technology, p. 33 (bottom) Corbis/Sean Sexton Collection, p. 34 (left) National Museum of Science & Technology, p. 34 (right) 1998 Hiroyuki Kaijo/Rocky Mountain Bicycles, p. 35 (top) Corbis/Phil Schermeister, p. 35 (bottom) Courtesy of Para-Cycle, Inc., P.O. Box 1906, Windermere, FL 34786-1906 (www.para-cycle.com), pp. 36-37 PhotoDisc, Inc., p. 37 (top) PhotoDisc, Inc., p. 38 Ray Boudreau Illustration Tina Holdcroft: pp. 2-3, p. 37 Dave McKay: pp. 14-15, p. 17, pp. 23-26, p. 41 Albert Molnar: p. 13, p. 31, p. 39 Cover Photograph PhotoDisc, Inc.