9 A world of machines
Contents
1. Driven gear Driven gear Driving gear INVESTIGATION 9 10 Looking at gears GAD To investigate how a machine with gears makes a task easier Materials hand operated eggbeater or hand drill METHOD AND RESULTS Identify the driving gear and the driven gear or gears Rotate the driving gear and observe the motion of each driven gear Count and record the number of teeth on the driving gear and the number of teeth on each driven gear 2 Use the handle to rotate the driving gear slowly through one complete turn while your partner counts and records the number of turns completed by each driven gear DISCUSS AND EXPLAIN Which is larger the driving gear or each driven gear 0 Which moves faster the driving gear or the driven gears QO Is this system of gears working as a force multiplier or as a speed multiplier QO How many times does each driven gear turn for each rotation of the driving gear 2 Does the number of teeth on each gear seem to affect the way the gear system works In what way 9 A world of machines 289 Big wheels small wheels Different sizes and arrangements of gears are used to make wheels turn faster slower or in different directions A large driving gear makes a small driven gear move faster but in the opposite direction Hand operated eggbeaters and drills use this combination of gears to make them spin quickly A small driving gear makes a2. a Lean a ramp against the pile of books Measure and record the distance from the bottom of the ramp through a larger distance Escalators are moving ramps The winding mountain road in the photograph on the next page is also a ramp Imagine how much shorter the trip would be if the road went straight up the mountain but no vehicle would be powerful enough to use the road When an object is pushed up an inclined plane energy is transformed from the energy of movement kinetic energy into stored energy potential energy If an object at the top of an inclined plane is allowed to slide or roll down some of its potential energy is transformed back into kinetic energy Inclined planes at work Wedges are inclined planes They can be used to penetrate or split objects or to stop them from moving Axes knives and your front teeth are examples of wedges They reduce the force needed to cut through objects If you have ever tried to cut through a hard to where it meets the top edge of the pile of books Place the 500 gram mass at the bottom of the ramp and use the spring balance to slowly pull it until its far end reaches the top of the pile Record the force measured by the spring balance DISCUSS AND EXPLAIN O Does it take more force to lift the mass straight up or along the ramp O In which case does the mass have to move further straight up or along the ramp QO Which method of raising t
3. a Draw an arrow to show where the effort is applied when turning right b Label the wheel and the location of the axle c What is the load being moved by the steering wheel d Is the steering wheel a force multiplier or a speed multiplier e If you wanted to change your steering wheel to one that was easier to turn should you get a larger one or a smaller one A car steering wheel is a wheel and axle machine TT ou is 8 Draw up a two column table with the headings Force multipliers and Speed multipliers List as many wheel and axle machines as you can think of in the appropriate column J It has been said by many people You don t get anything for nothing How does this statement apply to multiple pulley systems that make it easier to lift a load 10 Complete the equation load x load distance effort x 288 Science Quest 7 11 In the diagram below which of the systems P Q and R would you need to a apply the least effort b apply the most effort c pull the string through the greatest distance d apply an effort equal to the load e apply an effort equal to half of the load i System R Ue oa Load N Effort 12 Make a model wheel and axle Use cotton thread and two sets of slotted weights to show how your model can be used as a force multiplier a Calculate the mechanical advantage of your wheel and axle b Does your model change energy from one fo
4. Load Load The pulley systems to be tested in the experiment a single pulley b two single pulleys c two double pulleys QO How does the effort needed to lift the load with two double pulleys compare with that needed to lift it with one single pulley Would it be true to say that the system with two double pulleys has the same advantage as one with four single pulleys Why Looking at your tabulated results how would you say the effort needed changes as the number of pulleys increases Oo How does the effort distance change as the effort itself decreases Predict how much effort would be needed to lift the same load by 5 cm if you used two triple pulleys instead of two double pulleys How far would you need to pull on a string to lift the load 5 cm Effort N Two single pulleys f OP Two doubte pulleys 9 A world of machines 287 UNDERSTANDING AND INQUIRING REMEMBER 1 Which part of a circular doorknob is the wheel Which part is the axle 2 Explain why a circular doorknob is called a force multiplier 3 Explain why a ceiling fan is called a speed multiplier 4 How is a single fixed pulley useful even though it does not decrease the size of the force needed to lift a load 9 Why Is a system of two single pulleys better than one single pulley for lifting very heavy loads 6 What is a block and tackle What is it used for Draw a diagram of the car steering wheel shown below
5. MEAN The word robot comes from the Czech word robota meaning forced labour 9 A world of machines 293 UNDERSTANDING AND INQUIRING 1 What is the difference between a simple machine and a compound machine 2 What are sprockets 3 Which type of simple machine do bicycle pedals act as 4 Which class of lever is a bicycle handbrake 3 Where do the following compound machines get the energy from to move and make things happen a Bicycle b Car c Train 6 Why Is it necessary to use more energy to operate a machine than you can get out of it 7 How do robots differ from other machines 8 Suggest two reasons why steam was replaced by petrol as a fuel for cars 9 Where is the load that a bicycle handbrake pushes against 10 Is a bicycle handbrake a speed multiplier or a force multiplier Explain your answer 11 Machines are used to replace various parts of the human body Artificial arms hands and legs are all machines More recently artificial hearts have been implanted What are the arguments for and against the use of a machine to replace a failing human heart What do you think 12 List some reasons robots would be very useful for packaging food products 13 Robots are clearly very useful devices They do however have some disadvantages Construct a table to list the advantages and disadvantages of robots 14 Should robots be used to replace humans wherever possible in jobs that are unplea
6. a load of 6 coins with an effort of only 3 coins the mechanical advantage is given by mechanical advantage load effort 6 3 2 In other words the lever lifts a load that is two times greater than the effort The mechanical advantage of this lever is 2 Load 6 coins Effort 3 coins Ruler Levers with the effort between the fulcrum and the load are called third class levers Third class levers are not force multipliers They move a load through a larger distance than the effort moves in the same time and are therefore speed multipliers The softball bat shown above right is a third class lever Golf clubs tennis racquets and brooms are also third class levers designed to move a small load quickly with a large effort HOW ABOUT THAT Tooth decay was common on the goldfields of Australia in the nineteenth century because of poor diet and dental hygiene a i Rotting teeth were mre l A usually pulled out by e M a local doctor But if e a doctor wasn t around ae l the blacksmith did the job F ee Meee with the same pliers used sei abt E to pull the nails out of horseshoes Ouch oak 3 N i i a 7 1 How does the position of the effort affect its ability How does the position of the load affect the l el i i A softball bat is a third class lever designed to move a small load quickly INVESTIGATION 9 3 Pushi
7. direction Why do you think that it is called an idler gear Rack and pinion gears consist of a flat row of teeth called a Idler gear amp Driven gear Driving gear Circular rack and a circular gear wheel gear wheel Rack y A corkscrew uses rack and pinion gears to change the circular movement of the driving gears into the upward straight line movement that pulls the cork out This corkscrew uses rack and pinion gears c How could you change the design of the eggbeater so that it is easier to turn the handle What would be the disadvantage of doing this 7 Learn how gears are used to make a wheel turn faster by completing the Gears interactivity in your eBookPLUS int 0025 8 Investigate the effect of different sized gears by completing the Gear ratios interactivity in your eBookPLUS int 0746 9 Use Legotechnic or a similar kit to build a machine with at least two gears that can be used with a handle to a lift a heavy load b make a wheel turn in the same direction as the handle c make a wheel turn in the opposite direction from the handle e plus Which way Compound machines A bicycle is a compound machine made up of many simple machines The obvious ones are the front and rear wheels handbrake and pedals But if you look carefully you can find many others All compound machines are made up of two or more simple machines including levers whe
8. insert the screw halfway into one of the blocks of wood Look closely at the thread of the screw as It moves into the wood Does the wedge make it easier to separate the two blocks DISCUSS AND EXPLAIN amp Would you have been able to get the screw halfway into the wood by pushing straight down on it UNDERSTANDING AND INQUIRING CD 1 What is a ramp 2 Ramps are inclined planes List two other types of inclined planes 3 What energy transformation takes place when an object is pushed up an inclined plane 4 What is the difference between the thread of a screw and the pitch of a screw 284 Science Quest 7 This winding mountain road is a ramp Handle Rubber bands 39 A ramp makes it easier to push or pull objects upwards What is the penalty for making the task easier 6 Explain why inclined planes are classified as force multipliers 7 Construct a table with three columns headed Ramps Wedges and Screws Brainstorm with a partner or small group to list as many examples of each type of inclined plane as you can 8 Explain how a ramp is able to produce a mechanical advantage systems Wheels and axles ea E A circular doorknob is a simple machine called a wheel and axle It is actually a lever that can rotate The inner smaller wheel of the doorknob is the axle When you open a door you apply an effort to the wheel and the axle pulls on the load to open the door T
9. is the frame around the pulleys The tackle is the string or cable joining the load to the effort With a block and tackle it is possible to lift many times your own weight Of course you have to pay for it by pulling over a long distance The woman in the photo above is using the pulley to transfer energy from herself to the weight to make it move In order to move the load her muscles need to transform the chemical energy that she has stored by eating food into movement energy of her arms A block and tackle system is used in garages to lift engines out of cars It is also used on cranes wharves and ships HOW ABOUT THAT Archimedes 287 212 BC a Greek mathematician invented the multiple pulley system It is believed that he boasted to King Hiero II of Syracuse Give me a place to stand on and shall move the whole Earth The king challenged Archimedes to prove it Archimedes responded by using a system of pulleys to single handedly drag a ship fully loaded with cargo and passengers out of the water and onto land INVESTIGATION 9 9 Lifting that load AIM To compare the mechanical advantage of three pulley arrangements Materials 2 single pulleys 2 double pulleys 1 metre length of string set of slotted 50 gram masses 5 0 newton spring balance metre ruler hook from which to suspend pulleys METHOD AND RESULTS Draw up a table for your results like the one below a Ji Loa
10. the load effort and fulcrum on a copy of each of the levers shown below a Which of the levers are speed multipliers b Which of the levers are second class levers 11 Explain why third class levers are called speed multipliers 12 a What is the mechanical advantage of the lever in Investigation 9 4 when one coin Is used to lift a load of three coins b To increase the mechanical advantage of the ruler and pencil in Investigation 9 4 to lift a slightly larger load which way would you need to move the three coins 13 Explain why door handles are placed as far away from the hinges as possible 14 Create a poster or short series of PowerPoint slides that could be used to encourage people to warm up before going for their daily run around the block 15 Find out what the scientists in the Movement Science Department of the Australian Institute of Sport are researching to improve the performance of Australian athletes 16 Serious athletes don t just warm up They also go through cooling down exercises after strenuous activity Find out why they do this 17 Learn how a spanner multiplies force by completing the Spanner interactivity in your eBookPLUS int 0023 S OQ Loaded levers Pushing uphill Imagine how difficult it must have been for the ancient Egyptians to build the pyramids at Giza The Great Pyramid was built from over 200 million blocks of limestone most with masses over 2 tonnes It is bel
11. the turning effect of a force The turning point of a lever is called its fulcrum The resistance to motion that a lever works against is called the load The force used to cause movement is called the effort WHAT DOES IT MEAN The word ever comes from the Latin word evare meaning to make lighter The lever shown in the illustration below is a first class lever The fulcrum lies between the effort and the load A seesaw is another example of a first class lever First class levers are force multipliers because they multiply your effort Effort Spoon being used as a first class lever 218 Science Quest 7 The wheelbarrow and nutcracker shown below are also force multiplying levers However the load is between the fulcrum and the effort Such levers are called second class levers A door not a sliding one is another example of a second class lever 7 aA eee Sn oie lie What s the advantage The advantage of force multiplying levers is that they allow you to move a heavy load with a small effort Effort AT N F Ta gt Fulcurm gt Load Effort The wheelbarrow and nutcracker are examples of second class levers They allow you to move large loads that you would not be able to move without help The mechanical advantage of a force multiplying lever is defined as mechanical advantage load effort For example when you use the lever below to raise
12. 9 A world of m lt Engineers use scientific knowledge to machines that make life easier bridg heavy loads and buildings that don Machines transfer energy to ort frg 1 object by the action of a or V use machines every day to life easier sometimes vith even noticing The uma body could not move without the many simple machines inside Think about machines e How does a bathroom tap make life easier Where can you find machines inside the human body Who s the boss you or your car How could you lift many times your own weight by yourself How did Archimedes try to prove that he could single handedly move the whole Earth Why do bicycles have gears Why do roads wind around mountains instead of going straight up In this chapter 9 1 Ahelping hand 278 9 2 Pushing uphill 283 9 3 Systems Wheels and axles in aspin 285 9 4 Getting into gear 289 9 5 SCIENCE AS A HUMAN ENDEAVOUR Compound machines 291 9 6 Thinking tools ed bubble maps and Venn diagrams Study checklist Digital re resources 295 Looking back 296 projectsp u Paper Scissors Robot 297 YOUR QUEST Exploring simple machines A machine is a device that makes a physical task easier That means that cars bikes cranes lifts and escalators are machines But machines like these are actually made up of many smaller machines called simple machines Simple machines transfer energy from one object to another to make it move or
13. ake pads that push against the wheel Handbrake Sprockets On four wheels The car is also a compound machine But it is made up of many more simple machines than the bicycle Most of the simple machines in a car are under the bonnet but the most obvious ones are the wheels and axles that roll along the road and the steering wheel HOW ABOUT THAT One of the first bicycles invented was Called the swiftwalker It didn t have pedals The rider had to push off the ground with one foot to make the bike go forwards The rider could then sit while the bike coasted forwards Going downhill was a breeze but imagine trying to go uphill To make matters worse the wheels were made of wood with iron rims covered with leather It was a very bumpy ride 9 Aworld of machines 291 292 The front wheel and axle of this vehicle act as a speed multiplier A very large force moves the axle in a small circle The outside edge of the wheel turns in a large i circle and much faster than the axle Fuelling compound machines Machines don t create energy They reduce the effort you need to apply or they reduce the distance over which you need to apply a force The Law of Conservation of Energy applies to all machines The total energy you can get out of a machine is equal to the amount of energy that you or a fuel puts in However the total amount of useful energy you get out of a machine is always less than th
14. change direction INVESTIGATION 9 1 As simple as a spoon AIM To explore how a lever can make a task easier Materials Milo can with lid or similar teaspoon METHOD AND RESULTS Place the lid firmly on the can Try to remove the lid without using the teaspoon If you succeed in removing the lid replace it Use the teaspoon to remove the lid Replace the lid again Use the teaspoon to remove the lid again but hold the spoon much closer to the end near the lid DISCUSS AND EXPLAIN How does the teaspoon make it easier to remove the lid 2 Where should you hold the spoon to lift the lid most easily x assess On INVESTIGATION 9 2 Hard as nails AIM To investigate the use of a lever to remove a nail from wood Materials claw hammer nail in a block of wood METHOD AND RESULTS Try to remove the nail from the block of wood without the hammer Take care that you don t hurt your hand gt Now use the hammer to remove the nail DISCUSS AND EXPLAIN D Would you have been able to get the nail into the block of wood without the hammer Does the hammer make it easier to remove the nail 3 Where should you hold the hammer to make it easier to remove the nail Hammer Nail 9 Aworld of machines 277 A helping hand Can openers scissors tongs spanners hammers brooms tennis racquets and staplers are levers A lever is a simple machine that uses
15. d the slotted masses Effort to a mass of 400 grams and attach them to one Load end of the string Use the spring balance to measure the weight in newtons N of the slotted masses This weight is the load that must be lifted Record the load in your table Thread the other end of the length of string over the wheel of a single pulley and attach it to the spring balance as shown in diagram a above gt Pull slowly on the spring balance so that the load is lifted slowly and steadily upwards through a distance of 5 cm amp Record the force in newtons N measured by the spring balance This force is the effort Also record the distance through which you had to pull the spring balance to lift the load 5 cm The distance moved by the effort your pull on the spring balance is called the effort distance Arrange the system with two single pulleys as shown in diagram b The pulleys should be about 10 cm apart Pull slowly on the spring balance to lift the load steadily Lifting a load with pulleys lent Load N Single pulley 5 0 In your table record the force and effort distance needed to lift the load through a distance of 5 cm Repeat the previous two steps using the system with the two double pulleys shown in diagram c DISCUSS AND EXPLAIN 5 How does the effort needed to lift the load using two single pulleys compare with that needed to lift it with one single pulley i
16. d with a large effort Raising a load with a first class lever Your elbow is the fulcrum It is the turning point of the lever The load is the weight that you are trying to lift upwards The effort is between the fulcrum and the load so your forearm is acting as a third class lever and a speed multiplier When you bend your arm to lift a load your forearm acts as a third class lever Biceps contracts and pulls Triceps relaxes When you straighten your amy arm to push downwards such as when you do push ups or push a weight down your forearm acts as a first class lever and force multiplier The fulcrum is your elbow The effort is provided by your triceps muscle which is joined to a bone in your forearm called the ulna The load is the resistance to your downward push In this case the fulcrum is between the effort i and the load Biceps relaxes Triceps W contracts and pulls s Ti When you straighten your arm to bn push downwards your forearm I acts as a first class lever Kicking a ball When a football is kicked bones in the lower leg act as a third class lever The knee is the fulcrum The effort needed to straighten the leg is provided by muscles attached to the top of the lower leg Fulcrum The lower part of the footballer s leg pivots around the knee The knee is the fulcrum in this lever Load The load moves a long distance Effort Most of the effort
17. e amount that goes into it That s because some energy is always lost to the machine or the surroundings as heat Many simple machines and some compound machines including bicycles scooters and skateboards are fuelled by the energy a person provides Most motor vehicles are fuelled by petrol gas diesel or ethanol Before 1920 many cars were fuelled by steam Science Quest 7 transferring the energy of the gas particles to drive a motor which turned the wheels The steam was obtained by burning coal or wood to boil water Steam engines were much more suitable for fuelling trains than cars because they could carry large amounts of coal or wood on board Even though steam fuelled trains have been largely replaced by diesel or electric trains there are still many in service throughout the world Steam fuelled trains are still in use throughout the world often as popular tourist attractions Well oiled machines Friction is an enemy of compound machines and some simple machines such as wheels and axles gears and pulleys When moving parts rub against each other they heat up and cannot move quickly To avoid problems caused by friction the moving parts of machines need to be e kept free from dirt and dust e lubricated with grease or oil As mechanical systems machines are designed to transfer energy by the action of a force Energy transferred within a machine as heat is energy wasted Compound machines are d
18. ee where various efforts need to be placed to raise loads of 5 4 or 2 weights O Record your observations in your table A word about energy Although levers can multiply a force or speed the Law of Conservation of Energy is never broken The Law of Conservation of Energy states that energy cannot be created or destroyed It can only be transferred to another object or transformed into a different form You can never get more energy out of a lever than you put in Body levers Many of the bones in your own body are levers The long bones in your arms and legs are the most obvious examples of levers Joints such as your elbow and knee act as fulcrums Your muscles pull on part of the bone to provide the effort The load is the resistance to motion that your bone works against The load could be the weight of a basketball a soccer ball a bucket of water or a heavy weight in the gym Levers in your arm When you bend your arm to lift a weight the effort is provided by your biceps muscle where it joins a bone called the radius in your forearm just below the elbow 280 Science Quest 7 Do some more testing including raising small loads with a small effort DISCUSS AND EXPLAIN QO Why is this type of lever called a force multiplier QO Examine the completed table to see whether any pattern is evident in your data What is your conclusion GD Is there any advantage in using a seesaw type lever to raise a light loa
19. els and axles pulleys and gears On your bike Front and rear wheels Each of the front and rear wheels is an example of a wheel and axle The rear wheel is made to turn by another wheel and axle the pedals The axle of the pedals is joined to the axle of the rear wheel by a chain The rear wheel and axle is a speed multiplier The rear wheel axle is much smaller than the back wheel When it turns the back wheel turns very quickly The front wheel is pushed along the road by the rest of the bicycle Gears The gears on a bicycle usually act as speed multipliers Bicycle gear wheels are called sprockets Although the front and rear sprockets are connected by a chain they work just like gears with teeth that fit together The front sprockets are larger and have more teeth than the rear sprockets The highest wheel speed can be reached with the least effort when the larger front sprocket is used with the smallest rear sprocket This combination is most suitable when riding quickly on a level road When riding up a steep slope speed is less important If the smaller front sprocket is used with the largest rear sprocket you can climb the slope with less effort You do however need to make more turns of the pedals Handbrake The handbrake is an example of a first class lever The fulcrum is between the effort and the load When the rider squeezes the handle of the handbrake the effort is transferred along a cable to the br
20. esigned by mechanical engineers and kept safe and in working order by mechanics The challenge for engineers is to design machines that are safe energy efficient and suitable for the conditions in which they are used Mechanics are to compound machines what medical practitioners are to people They are problem solvers keeping the machines they work on in good working order and finding ways to fix problems and in some cases detecting problems that have not been noticed before Untouched by human hands Robots are compound machines that perform physical tasks without direct human assistance They can be used to do jobs that are unpleasant dangerous or boring Robots can work in hot weather cold weather under water under the ground in outer space and in noisy places They don t spread germs and they don t get tired Most robots are controlled by computers Some are guided by remote control units similar to those used to operate DVD players and TV sets Some robots can see and hear using video cameras and microphones aum A N imma u PE y mpe Eel Rel os Lm E Most robots are used to perform simple tasks that humans would find unpleasant boring or dangerous These robots are used to put the parts of a car body together Robot vacuum cleaners No time to clean the house Maybe a robotic vacuum cleaner can do the work for you These robotic vacuums are really compound machines that contain a va
21. gation looking at the effect of different sized gears Searchlight ID int 0746 9 Aworld of machines 295 D A Pim A 1 Copy the following diagrams and label the fulcrum load and effort on each of the levers The first diagram is labelled for you 2 A student uses a pencil and ruler to model a first class lever It is tested by lifting 20 cent coins placed at one end of the ruler a Draw a diagram to show how a pencil and ruler can be set up to model a first class lever Label the fulcrum effort and load b Calculate the mechanical advantage of the lever when it uses four coins to lift 12 coins c If the 12 coins are placed six centimetres from the fulcrum how far should the four coins be from the fulcrum to lift the larger pile of coins D 3 A flight of stairs is an example of a simple machine a Which simple machine is a flight of stairs most similar to b Are stairs force multipliers or speed multipliers Explain your answer oo 4 Which of the following is a speed multiplier and which is a force multiplier Driving gear Morven Driven gear gear Driving gear 9 The plank below is 3 6 metres long It is being used as a g lever to lift a 40 kilogram box This represents a load of 400 newtons be a a 5 m i Ta z J E ihe p ede 296 Science Quest 7 Link to assessON for questions to assess J test your readiness FOR learni
22. he fulcrum or turning point is at the very centre of the doorknob The doorknob in the photo is a force multiplier You apply a small effort to the wheel to move a large load with the axle There is however a penalty you pay for the extra force with extra distance The wheel handle moves further than the axle Imagine however how difficult it would be to turn the axle without a handle Bathroom taps and car steering wheels are also force multiplying wheels and axles Can you think of any others This doorknob is a wheel and axle machine The handle is the wheel which turns in a circle The spindle inside is the axle and it turns ina smaller circle Speed it up Wheel and axle machines can be used to make things move faster The ceiling fan in the photograph below is a wheel and axle machine A large force is applied to the axle Each time the axle turns the fan blades move a much greater distance in the same amount of time It is a speed multiplier The ceiling fan transfers kinetic energy from the motor that makes the axle turn to the fan blades A car wheel is another example of a speed multiplier The axle This ceiling fan is a speed multiplying wheel and axle machine The fan blades trace out a complete circle Electricity is used to make the axle turn and the fan blades move faster than the axle INVESTIGATION 9 7 Getting a handle on wheels and axles AIM To investigate how wheels and a
23. he mass is better Why The mechanical advantage of a simple machine Is a measure of the number of times greater a load is than the effort see section 9 1 What is the mechanical advantage of your ramp 9 A world of machines 283 piece of food like an apple with a blunt knife you will know the value of a wedge Screws are inclined planes A screw is a curved ramp However instead of an object being pushed up the ramp the ramp is pushed down into the object The ramp cut into a screw is called the thread the distance between two turns of the thread is called the pitch Because the total length of the thread is so great its force multiplying effect is very large Most car jacks use a large screw to lift a huge load with little effort Similarly a corkscrew is used to penetrate the tightly fitted cork of a wine bottle with little effort The cork is then removed by pulling the corkscrew out directly INVESTIGATION 9 6 Inclined planes on the move AIM To investigate how a wedge makes a task easier Materials wooden door wedge 2 rubber bands 2 blocks of wood soft pine METHOD AND RESULTS Use two rubber bands to hold the two blocks of wood together Try to pull the two blocks of wood apart with your fingers Take care not to break the rubber bands self tapping screw screwdriver Place the sharp edge of the door wedge between the two blocks and push it down Use the screwdriver to
24. ieved that the blocks were dragged from nearby quarries by gangs of men The task of lifting the blocks to heights of over 140 metres was made possible by building long ramps of brick and sand As each layer of limestone blocks was completed the ramps were extended so that the next layer could be commenced WHAT DOES IT MEAN The word ramp comes from the Old French word ramper meaning to climb Inclined planes A ramp is a machine because it makes the physical task of raising an object easier A ramp is simply an inclined plane a surface that is set at an angle to the horizontal It allows objects to be raised with less effort than would be needed to lift them straight up Ramps are used in shopping centres and other buildings to allow wheelchairs prams and strollers to be raised with less effort Although a smaller effort is needed when using a ramp the load must be moved INVESTIGATION 9 5 Inclined to make it easier AIM To investigate how an inclined plane makes a task easier Materials 3 textbooks 500 gram mass with hook METHOD AND RESULTS Place three textbooks on top of each other Measure and record the height of the textbooks Place the 500 gram mass next to the pile of books and use the spring balance to slowly lift the mass so that its base is level with the top of the pile ramp thin piece of wood spring balance D Record the force measured by the spring balance
25. large driven gear move slower but in the opposite direction This arrangement acts as a force multiplier It is used to move large loads with a small effort This arrangement is used in cars to allow them to climb hills or gather speed quickly It is also used in rotating shopwindow displays to make them turn slowly Pairs of gears the same size change the direction of turning without changing the speed UNDERSTANDING AND INQUIRING REMEMBER 1 What are gears 2 What is the difference between a driving gear and a driven gear 3 Which gear turns faster if a the driving gear is larger than the driven gear b the driving gear is smaller than the driven gear c the driving gear is the same size as the driven gear 4 What can gears do other than make another wheel turn faster 9 List as many devices that use gears as you can 6 The driving gear on a hand operated eggbeater has 40 teeth while each driven gear has 10 teeth a How many times will the blades of the eggbeater turn for each turn of the handle b How could you change the design of the eggbeater so that you could move the blades faster without moving the handle faster 290 Science Quest 7 Gear wheels at right angles to each other can change vertical motion into horizontal motion Hand operated eggbeaters and drills use this arrangement An idler gear can be used between the driving and driven gears to make them turn in the same
26. lly better 20 Cars are compound machines that people rely on to get around Think of the advantages of having one but think also of all of the problems that cars cause air pollution is just one of them a Construct a table like the one below In a small group brainstorm the advantages and disadvantages of cars completing the table as you go b After you have completed your table discuss the questions with your group i Are cars our essential servants Could we live without them ii Do cars control our lives so much that they are our masters Are we slaves to our cars c Finally write one or two paragraphs to state your own opinion on whether the car is our servant or our master Include reasons for your opinion The car servant or master Advantages of cars 21 In a small team brainstorm a list of the simple machines that you might find inside a typical family car 22 List as many situations as you can in which robots could be used to rescue people where humans could not Disadvantages of cars LUDY CHECKLIST _ explain how a mechanical advantage can be obtained from simple machines such as levers inclined planes pulley systems and gears distinguish between speed or distance multiplying machines and force multiplying machines _ describe the effects of forces that can cause objects to change the motion of an object _ recall that you cannot get any more energy ou
27. m of a wedge while the movement of your forearm is possible because itis a lever with your elbow acting as the fulcrum The robotic hands that prosthetic engineers design are the result of combining processed materials such as metal alloys and polymers to create systems of simple machines that imitate the motion of a real hand as closely as possible Your task e You are going to design and build a robot hand that is capable of performing all of the hand motions used in the game of Paper Scissors Rock You will then use your robot hand to compete with those created by other student groups in your class to find the Paper Scissors Robot champions This tournament will be done as a round robin competition with each group playing every other group once Your robot hand must be sturdy enough to keep functioning throughout the tournament e You will also create a user s manual that goes with your robot hand This will provide a detailed diagram plan of your robot hand including an explanation of how itis constructed and how the user makes it move into the three different positions required In the back of the manual there should also be a Troubleshooter table that will tell the user what the most common problems are that they may experience when using the hand and provide solutions to fix those problems 9 Aworld of machines 297
28. ming up they can easily tear Even with warming up if muscles have not been prepared for sport by proper training they can easily be torn when sudden movements are made 9 Aworld of machines 281 UNDERSTANDING AND INQUIRING REMEMBER 1 Which body parts provide the effort when bones act as levers 2 When you bend your forearm upwards to lift a bucket of water it acts as a lever a Where is the fulcrum b Which muscle provides the effort c What is the load d Which type of lever is your forearm acting as 3 When you straighten your arm to do push ups your forearm acts as a lever a Where is the fulcrum b Which muscle provides the effort c What is the load d Which type of lever is your forearm acting as 4 Why is it important to warm up before playing sport 39 What is a lever 6 Explain why first class and second class levers are called force multipliers 1 Why can t you get more energy out of a lever than you put in 8 In cricket the arm acts as a lever when the ball is bowled a Which class of lever is the arm acting as a b Is the arm acting as a speed multiplier or a force multiplier Explain your answer Which part of the body acts as the fulcrum In cricket the bowling arm is used as a lever c 282 Science Quest 7 Shovel 9 Is height an advantage to tennis players and cricket bowlers Explain your answer 10 Label
29. needed to straighten your leg when kicking a ball comes from the muscles in your legs The effort to kick a ball is applied by muscles that attach to the top of your lower leg The load is the resistance to motion of the football Although there is little movement where the effort is applied the foot where the load is moves a large distance Anyone for tennis In ball games such as tennis cricket baseball golf and hockey racquets bats clubs and sticks are used as third class levers The end of the lever that strikes the load the ball moves much faster than the end of the lever where the effort is applied When a tennis ball is served the lever consists of your whole arm and the tennis racquet The fulcrum is your shoulder the effort is applied by the muscles attached to the bones of your upper arm and the load is at the centre When a tennis ball is served the arm and tennis racquet work together of the racquet as a third class The larger the lever and speed distance between multiplier the load and the effort the faster the serve Professional tennis players can serve tennis balls at speeds of up to 240 km h This is many times the speed of the upper arm where the effort is applied Why warm up The muscles that pull on your bones to make them move are made up of tough and elastic fibres When they are cold the muscles are less elastic If you overload muscles without war
30. ng your l progress AS you learn and your levels OF achievement www assesson com au a If the fulcrum were placed in the centre of the plank what downward effort would the man on the right of the diagram need to apply to raise the box b If the man wants to push down on the end of the plank with an effort of only 200 newtons i how far along the plank should the fulcrum be ii what would the mechanical advantage of the lever be c How could the mechanical advantage of the lever be increased d Is the plank being used as a speed multiplier or a force multiplier Explain your answer e Suggest a different way of using the plank as a simple machine to get the box into the truck Imagine that you wanted to drive a screw into a length of wood If you had a choice of using one of the screwdrivers illustrated on the right which one would you use State a reason for your choice A softball bat is an example of a speed multiplying lever a Explain why the softball bat is not a force multiplying lever b Where is the fulcrum of the softball bat c Which class first second or third of lever is the softball bat d Which other lever is used to help the softball on its way at high speed The bicycle shown below is made up of many simple machines Identify as many as you can Classify the simple machines that you identify as levers inclined planes wheels and axles pulleys and gears If you l
31. ng your barrow AIM To investigate how a wheelbarrow makes lifting a load easier Materials wheelbarrow or plank if a wheelbarrow is not available a few bricks METHOD AND RESULTS Place a few bricks in the wheelbarrow and lift it by the ends of the handles Without changing the load lift the wheelbarrow with your hands as far down the handle as possible While holding the wheelbarrow up have your partner move the load so that it is closer to the handle to raise the load amount of effort needed to raise it 9 A world of machines Get a load of this GUD To investigate the relationship between effort and its distance from the fulcrum Materials ruler at least 30 cm long pencil 6 identical coins or 50 gram weights plasticine to hold pencil in place if it rolls METHOD AND RESULTS Draw up a table like the one on the right Use the pencil and ruler to set up a seesaw so that it balances without any weights on it Place a load of three weights 4 cm to the left of the fulcrum Place the other three weights the effort to the right of the fulcrum so that the effort balances the load B Record the distance from the effort to the fulcrum in your table Remove two of the weights from the effort and raise the load of three weights with an effort of only one weight amp Record the new distance from the effort to the fulcrum in your table Experiment with your seesaw to s
32. ook thoroughly you might be surprised at how many you find Create a poster or a series of PowerPoint slides to explain how one of the following machines works Ensure that you Indicate whether the machine is a speed multiplier or a force multiplier a Water tap b Eggbeater c Corkscrew d Bicycle gears Thinking tools Single bubble maps and Venn diagrams Summing up Looking back crossword e Book projectsplus Process oe Open the ProjectsPLUS application for this chapter Pm_ _ MA oOo located in your eBookPLUS Watch the introductory ICISSOrTS ROQOL video lesson and then click the Start Project button to set up your project group You can complete this project i SEARCHLIGHT ID PRO 0089 individually or invite other members of your class to Chanarin form a group Save your settings and the project will scenarid be launched Robots are highly advanced electrical machines that can be programmed to perform specific tasks Like all compound machines they are made up of many smaller interacting devices that are referred to by engineers as simple machines In general there are considered to be seven types of simple machine lever screw inclined plane gear pulley wheel and axle and wedge Our bodies are able to move around because the muscles bones tendons and ligaments also act like simple machines For example an incisor is really an organic for
33. riety of sensors motors and computer circuits They are able to sense how large a room is whether there is something blocking their path and how long it will take to get the vacuuming done They even find their way back to a charging station when they are low on battery capacity Most robot vacuums have five motors in total and are driven by two wheels controlled by two motors The robot can turn depending on how fast each wheel turns A third wheel can freely rotate and balances the robot The other three motors control the vacuum suction the side sweeping brush and an agitating brush What happens when the robot is brought into a new space to clean It uses an infra red beam to measure the approximate distance across a room The computer then calculates approximately how long it should take for the robot vacuum to clean that room It starts vacuuming at the centre of the room and spirals out until it reaches the perimeter or an obstacle When either of these things happens the robot avoids bumping into the walls or obstacle using a short range infra red sensor Another infra red sensor is directed at the area in front of the robot Usually the return signal occurs very quickly from the ground which is not very far away However if stairs or a void are encountered the return signal takes longer this is called the cliff effect this is detected by the robot and it turns around or backs up to avoid disaster WHAT DOES IT
34. rm to another If so describe the change in detail 13 Investigate the wheels and axles on a bicycle a How many are there b What is the purpose of each wheel and axle c What is the purpose of the chain 14 Find out more about Archimedes and the machines he invented He is probably more famous for Archimedes Principle than for any of his inventions What is Archimedes Principle e plus Q Measuring forces Getting into gear Most people associate gears with cars or bikes but you can also find gears in the kitchen A hand operated eggbeater has gears that are used to change both the direction and speed of motion Each of the gears in a clock is simply a wheel and axle with teeth The teeth of one gear fit between the teeth of another gear When one gear turns the other can be made to turn faster slower or in a different direction The gears in the clock allow the three hands to move around the face of the clock at different speeds The wheel that is moved first is called the driving gear Usually the driving gear is moved by a person or a motor On a bicycle it is moved by pedalling while in the eggbeater shown at left the driving wheel is moved by the handle The wheel that is moved by the driving gear is called the driven gear In a hand operated eggbeater there are two driven gears The gears in this clock allow its three hands to move around its face at different speeds
35. rs Materials selection of wheels and devices for example doorknob hand drill toy cars spinning toys wind up toys taps screwdrivers wing nut small wheels METHOD AND RESULTS Examine the wheel and axle machines provided Draw a diagram labelling the wheel and axle For each machine examined T Write down whether it is a force multiplier or a speed multiplier a Explain in your own words how it works Getting a lift A pulley is a special type of wheel and axle that makes it easier for you to lift a load The wheel has a groove around it so that a rope or cable can be passed over or under it A pulley does not decrease the size of the force or effort needed to lift the load It changes the direction of the effort It is easier to pull down on a rope to lift a load than it is to push the load Your own weight can be used to advantage When more than one pulley is used a large load can be lifted with a small effort A system of two or more pulleys therefore acts as a force multiplier It magnifies the size of the effort As with other force multipliers there is a cost The rope needs to be pulled through a large distance to move the load through a small distance 286 Science Quest 7 A single pulley simply changes the direction of the effort needed to lift a load O A bockand macke A multiple pulley system is is used to lift or usually called a block and tackle pull heavy loads The block
36. sant or boring Write your opinion and reasons for it 15 Find out how hydraulic machines such as hydraulic lifts cranes or brakes work 16 Find out what qualifications are needed to become a a mechanical engineer b motor mechanic 17 Use the internet or other resources to investigate one of the Australian inventions listed above right Each of them is a Compound machine Report on when and by whom it was invented how it works and how it makes life easier Identify at least three simple machines that make the invention work 294 Science Quest 7 a Rotary clothes hoist b Victa lawn mower c Stump jump plough 18 Microbots are robots that are small enough to be Injected into your veins Use the internet to answer the following questions about microbots a Which harmful things in your bloodstream could microbots be used to destroy b How does the size of a microbot compare with the size of i a bacterium ii a human red blood cell 19 It is the year 2050 Computer controlled robots are used to perform most jobs that humans did in the past Teachers have been replaced by robots that talk answer questions set homework mark tests and even punish misbehaving students Robots drive cars serve in shops babysit children and even read the news on television a Write a story about a day in the life of a student your own age in the year 2050 b What do you think about this imaginary year 2050 Is it rea
37. t of a machine than you put in _ describe the action of levers in the human body COMPOUND MACHINES _ distinguish between compound machines and simple machines L identify how simple machines work together in compound machines such as bicycles lifts cranes and hydraulic brakes C DIGITAL RESOURCES ANSWERS for this chapter can be found online in your eBookPLUS Online section Individual Pathways Activity 9 1 Activity 9 2 Activity 9 3 Investigating Analysing Investigating mechanical mechanical mechanical systems systems systems further doc 6060 doc 6061 doc 6062 FOCUS activity Access more details about focus activities for this chapter in your eBookPLUS doc XXXX _ explain how friction can be reduced in machines to reduce energy losses SCIENCE AS A HUMAN ENDEAVOUR _ explain how inclined planes made tasks easier in an ancient civilisation _ identify that mechanics and mechanical engineers need to know how simple and compound machines work to apply forces _ explain how sports scientists can use their knowledge of levers in the human body to improve the performance of athletes _ consider and discuss the advantages and disadvantages of a dependence on cars for transport _ identify some of the benefits of robots to humans Interactivities Searchlight ID int 0023 Gears Learn how gears are used to make a wheel turn faster Searchlight ID int 0025 Gear ratios An investi
38. xles make a task easier Materials screw firmly embedded in a block of wood screwdriver METHOD AND RESULTS Try to remove the screw from the block of wood with the screwdriver by turning the shaft instead of the handle Handle Remove the screw by Blade using the screwdriver as itis meant to be used by turning the handle A screwdriver is Use the a wheel and axle screwdriver to replace the screw firmly into the wood Can the screw be removed by turning the shaft DISCUSS AND EXPLAIN D What difference does using the handle make to the effort needed to remove the screw During one full turn of the screwdriver which moves further the outside edge of the handle or the outside edge of the shaft turns when a large force is applied to it The outside of the wheel moves faster covering a much greater distance in the same time Pairs of wheels and axles are sometimes joined together with a chain or belt This either reduces the effort needed to make one of the wheels turn or makes one of the wheels turn faster The fanbelt in a car is one example Wheels and axles joined by belts are also used to operate heavy machinery in factories 9 A world of machines 285 J i p a These wheels and axles are joined by a belt to operate heavy machinery INVESTIGATION 9 8 Wheels and axles at work AIM To investigate how wheels and axles can become force or speed multiplie
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