Simple machines OBJECTIVES When you have completed this lesson you will be able to: identify some common simple machines explain how simple machines make work easier A machine is an invention that makes work easier. A simple machine increases the strength of a push or a pull (a force), or the distance of a movement, to complete a task easily. With a nutcracker you increase the force from your hand to crack a hard nut. A long fishing rod increases the distance moved by your arm to cast a line. Can you name these everyday machines? Write a sentence to say what each does. The first two have been done for you. Nutcracker: Increases the force from your hand to crack a hard nut. Pulley: Changes the direction of a force to lift something up as you pull down. Make a display of machines in the classroom. Test each to see how it works. 54
Inclined plane An inclined plane or ramp is one of the simplest machines. It is easier to push something up a gentle ramp than up a steep one. Investigating inclined planes You will need: a smooth plank, a pile of bricks, a heavy weight. Make an inclined plane by resting one end of the plank on a brick. Push the weight (your ) up the slope. Now add another brick to make the slope steeper. Push the weight up the new slope. Does this need more or less effort? The ancient Egyptians built the great pyramids as tombs for their kings. They had to move giant blocks of stone without modern cranes and trucks. They might have used logs as rollers. FASCINATING No one knows who invented the first wheel. Models of carts and chariots with wheels have been found in ancient Egyptian tombs. They are more than 4000 years old. roller inclined plane Perhaps rollers gave an inventor the idea for the wheel! The wheel is one of the most useful inventions. 55
Using rollers You will need: a heavy book, round pencils. 1 Lay five pencils on a table about 5 cm apart. 2 Lay the book on the pencils. 3 Slide the book over the pencils. How easily does it move? 4 When the book has passed over the last pencil, pick up the pencil and move it to the front so that the book can carry on moving. Carry on moving the book by taking the rollers from the back to the front, one at a time. This is how Egyptians could have moved their stone blocks. What you have learnt Copy and complete these sentences using the key words. A machine is an that makes work easier. It may increase the strength of a or the distance of a. The idea for inventing the wheel may have come from using to move s. Another word for a ramp is an. KEY WORDS force inclined plane invention movement rollers Check your progress 1. What is a machine? 2. Name three everyday machines and explain what they do. 56
Levers OBJECTIVES When you have completed this lesson you will be able to: explain how tools such as scissors, crowbars and fishing rods work as levers investigate the action of a lever A lever is a simple machine made with a rod or a bar. A see-saw is a lever. It has a in the middle where it turns. If you push down on one end of a see-saw, the other end goes up. A light person can balance a heavier person on a see-saw. The lighter person must sit further from the. Effort and You will need: a long plank (the lever), a heavy bag of sand (the ). 1 Lay the plank on the floor. 2 Feel how heavy the is by lifting it using your arms. 3 Place the on the plank near one end. Use one hand to raise the by lifting the far end of the plank. Is it easier than lifting the directly? 4 Try placing the in different positions along the plank. 5 Which position makes it easiest to lift? How high does the rise? Does it rise as far as your hand? effort In this activity the plank is a lever. The end that stays on the floor is the. The force you use to move the lever is called the effort. Because the effort is further from the than the is, you can lift a large with a small effort. FASCINATING You never get something for nothing! If you use a lever to increase a force, the distance moved is less. If you use a lever to increase the distance moved, the force needed is more. 57
effort effort U N I T 2 M A C H I N E S Scissors Can opener Pliers Bottle opener Oar Levers in action These effort machines work as levers. Copy the diagrams. Use the words effort, or to fill in the boxes. effort effort Barrow Tongs effort Can opener Scissors Pliers effort effort Crow bar Tongs Barrow effort Can opener effort Crow bar What you have learnt Copy and complete these sentences using the key words. A lever is a rod that turns on a. You can use a lever to raise a large with a small. To do this the must be close to the. Check your progress 1. Make a drawing to show how you can raise a heavy sack off the ground by using a plank as a lever. Label the, effort and. 2. Describe an everyday machine that works as a lever to increase a force. effort Tongs FASCINATING effort Your jaws (like pliers) are a pair of levers. Your back teeth are closer to the hinge of your jaws than your front teeth so you can bite harder with your back teeth. KEY WORDS effort 58
Pulleys OBJECTIVES When you have completed this lesson you will be able to: explain how a pulley transfers force and motion investigate the use of pulley systems to increase forces A pulley is a special kind of wheel. It has a groove on the outside for a string or rope. You can raise a flag up a pole with a simple pulley. When you pull down on the rope, the pulley turns and the flag goes up. The pulley changes the direction of the force from down to up. Builders use pulleys to raise s, as shown below. pull down pulley flag goes up You can make your own pulley with a cotton reel. Making work easier With two pulleys you can lift twice as much weight with the same effort. With more pulleys you can lift even heavier s. pull same pull single double 59
Pulleys working together Jo can lift one sack with a single pulley. With two pulleys he can lift two sacks. Look at these pulley systems. Count the pulleys lifting the. Copy the table and write down the number of sacks that Jo lifts with each system. Number of pulleys 1 1 Number of sacks Block and tackle A block and tackle is two sets of pulleys linked by a rope. A pull on the free end of rope draws the block and tackle together with a much bigger force. With a block and tackle one person can raise the sail on a ship. 60
Investigating pulleys You will need: two broom handles, a length of strong rope. 1 Tie one end of the rope near the middle of one broom handle as shown. 2 Two people should now hold the handles. Loop the rope around the second handle. A third person pulls the free end of the rope to draw the handles towards each other. Can the two people holding the handles keep them apart? 3 Now take a second loop around the handles and repeat the experiment. Is it harder or easier to hold the handles apart? 4 Repeat with a third loop and further loops. In this activity two broom handles work as a block and tackle. The more loops of rope between the handles, the greater the force pulling them together. What you have learnt Copy and complete these sentences using the key words. A is a wheel with a groove for a string or rope. It can change the direction of a force. Two sets of pulleys linked together as a increase the force with which a rope is pulled. KEY WORDS block and tackle pulley Check your progress 1. Draw a diagram to show how a flag can be raised up a pole by pulling down on a rope. 2. A man can lift a 50 kg. The mass of a car engine is 200 kg. Describe a simple machine that the man could use to raise the engine. 61
Screws OBJECTIVES When you have completed this lesson you will be able to: explain how devices such as wood screws, bottle tops and car jacks use screw threads to increase forces make a model of a screw thread A screw has a groove which winds round and round a spiral shape. The spiral groove is called a thread. When you turn a wood screw the thread cuts into the wood. With each turn the screw is pulled into the wood by one thickness of the thread. You can t push a screw into wood with your bare hands. The screw thread multiplies your strength by winding the screw in, a little at a time. Using screws These items use a screw to multiply a force. Write a sentence to say what each one does. The first two have been done for you. drill Nut and bolt: Tightens and grips to hold something in place. vice Screw top: Seals a jar tightly to keep the flavour in and germs out. corkscrew Make a classroom display of items with screw threads. Try each one out to see how it works. 62
How a screw works Screws multiply effort. All the effort to turn them is concentrated into a small movement inwards. This produces a very large force. one turn spiral thread forward movement Making a thread You will need: paper, pencils, scissors. Have you ever walked up a spiral staircase? The stairs take you up a slope like straight stairs, but you go round and round at the same time. This diagram shows how you can make a spiral thread by wrapping a paper triangle around a pencil. The pitch of the thread is the distance between loops. Investigate how the pitch of the thread depends on the angle of the triangle. pitch angle What you have learnt Copy and complete these sentences using the key words. A multiplies the effort you use to turn it. A spiral makes it move a small distance forwards with a very large force. The distance between loops of the threads is called the of the screw. FASCINATING By using a car jack you can lift a whole car with one hand! The screw in this jack magnifies the effort on the handle 200 times! Check your progress 1. Draw a diagram of a wood screw. Label the thread and pitch. 2. Explain how a screw multiplies the effort used to turn it. 3. Name three items that have a screw thread and explain their purpose. KEY WORDS pitch screw thread 63
Gears OBJECTIVES When you have completed this lesson you will be able to: describe how gears change the speed, force and direction of rotation identify the driving gear describe some machines that use gears A gear is a special wheel with teeth around its edge. One gear wheel turns another. Its teeth mesh with (fit between) the teeth on the second gear. When the first gear turns, its teeth push the teeth on the second wheel, making it turn as well. meshed teeth Two gear wheels with meshed teeth go around in the opposite direction. Gears transfer turning motion and forces from one place to another, for A-W 099 example from a car engine to the car wheels. Primary Science: Bright Ideas PB4 Using gears These things use gears to transfer turning motion and force. Write a sentence to say what each does. The first two have been done for you. gears gears gears spring minute hand Primary Hand drill: Science: Gears Bright Ideas Primary Clock: PB4 Science: Gears Bright transfer Ideas the PB4 A-W transfer 100a the turning A-W turning 100b force from the force from the handle spring to the hands. to the drill bit. hour hand Make a classroom display of devices with gears. Try each one to see how it works. 64
Gear speeds If two gears have the same number of teeth, they turn at the same speed and with the same force. 12 teeth 12 teeth drive gear same speed, same force Primary Science: Bright Ideas PB4 If one gear A-W 102 has 12 teeth but the other has only six, then the smaller gear turns twice for every turn of the bigger gear. So the smaller gear turns twice as fast, but with only half the force. FASCINATING Some bikes have six or more gear wheels called sprockets. They are linked by a chain so they turn in the same direction. The sprockets on the wheel are smaller than the drive sprocket on the pedals. So the wheel turns faster than the pedals. small sprockets large sprockets 12 teeth 6 teeth drive gear double the speed, half the force Primary Science: Bright Ideas PB4 A-W 105 Primary Science: Bright Ideas PB4 A-W 103 Look at these gears. In each case a drive gear turns a second gear. Can you predict how many turns the second gear will make when the drive gear turns once? (Hint: count the numbers of teeth on each gear. What is their ratio?) drive gear drive gear drive gear Primary Science: Bright Ideas PB4 A-W 104 You could use plastic gears from a construction kit to test your ideas. 65
What you have learnt Copy and complete these sentences using the key words. Gears are special wheels with. When the teeth on two gears, one turns the other. Gears transfer and forces from place to place. KEY WORDS mesh teeth turning motion Check your progress 1. Draw two meshed gears with the same numbers of teeth. Label this to show what happens when one gear turns clockwise. 2. Name three machines with gears. Explain what the gears do. 66
Using machines OBJECTIVES When you have completed this lesson you will be able to: describe how technology has changed over the years at a building site explain that a complex machine is a combination of simple machines This picture shows how a building site may have looked 150 years ago before motor vehicles or power tools. Everything was done by muscle power. The workers used simple machines to move s, dig holes and cut materials. Compare the two pictures. Can you find examples of these simple machines on either site? a lever a wheel a pulley gears. a screw thread Explain how the workers do these tasks on the different sites: lifting s drilling holes cutting wood digging holes. mixing cement On which site is the work easier? Explain why. Complex machines A complex machine is built up from two or more simple machines such as levers, wheels and pulleys. The parts work together to perform a task. This shows a modern building site. Now the workers use more complicated machines to make the work easier. Many machines are powered by petrol engines or electric motors. The builders do far more work in less time with these modern inventions. This bike is a complex machine. The handlebars and brakes are levers. Gears carry the force from pedals to wheels. Nuts and bolts with screw threads hold the parts together. 67
Copy these pictures which show two complex machines. Which simple machines are they made from? Decide if each part is a lever, a wheel, a crank, a screw or a gear then label it.????? fishing line?? Primary Science: Bright Ideas PB4 A-W 109b Primary Science: Bright Ideas PB4 A-W 109a Can you design a new machine? It could crack a nut, butter bread, open a door, wash a dog, or do some other task. Draw your machine and, if possible, make a working model. What you have learnt Copy and complete these sentences using the key words. A is built from simple machines that work together. Many modern machines are powered by a petrol or electric. KEY WORDS complex machine engines motors Check your progress 1. Name three machines on a modern building site that had not been invented 150 years ago. 2. What is a complex machine? Give an example. 68
The body as a machine OBJECTIVES When you have completed this lesson you will be able to: explain how parts of the body work as simple machines describe how the arm works as a combination of levers Through muscle power alone the human body can run at 40 km per hour, lift 400 kg, or turn a triple somersault. All these feats are possible because the body is a complex machine made from levers linked together. Your limbs are levers upper arm forearm Your joints are s shoulder elbow biceps muscle wrist thigh hip lower leg knee forearm elbow ankle The diagram above shows how your biceps muscle bends your arm at the elbow to lift a book. thigh muscle The forearm is the lever. The elbow is the. The biceps muscle supplies the effort to lift the. calf muscle Your muscles are the motors that power your movement 69
Kicking a ball Bend your leg at the knee, then straighten it as if to kick a ball. 1 Draw a diagram of your leg, similar to the diagram of the arm, to show how it works as a lever. 2 Label your diagram to show which parts are the lever and the. What is the? What supplies the effort? FASCINATING When you walk you use 200 different muscles and almost every joint in your body! Body maintenance Like all machines, you should maintain and use your body correctly to keep it working well. Regular exercise keeps your muscles and bones strong. Take care when lifting heavy s or you might damage your muscles or joints. Looking after your back You will need: sheets of paper. Roll a sheet of paper into a straight tube. Stand it straight up on the table. Feel how much weight it can support. Put a bend in the tube. How much weight will it hold now? Can you say why it is better to keep your back straight? You should always lift weights by bending your knees and keeping your back straight. Your back is not as strong when it is bent. 70
What you have learnt Copy and complete these sentences using the key words. The human body is a complex machine. Its are levers, its are s, its supply the effort to make its parts move. Regular helps to keep muscles and bones strong. KEY WORDS exercise joints limbs muscles Check your progress 1. Name two parts of the body that act as levers. Name the muscles powering these levers. 2. Explain why you must not lift a heavy with a bent back. How should you lift a? 71
End-of-Unit Test Select the one correct answer for each question. 1. The diagram shows a simple machine. What type of machine is it? (a) pulley (b) gear (c) lever (d) wedge 2. Name the part labelled X on the above diagram. (a) (b) (c) effort (d) pulley 3. The two masses on the pulleys are just balanced. What is mass M? (a) 5 kg (b) 10 kg (c) 15 kg (d) 20 kg 10 kg M 4. A screw is a simple machine. When you turn the screw it moves forwards: (a) with a smaller force (b) with the same force (c) by a greater distance (d) with a greater force 72
5. The diagram shows two gears. When gear 1 turns once clockwise, gear 2 turns: (a) once anticlockwise 1 2 (b) once clockwise (c) twice anticlockwise (d) twice clockwise Primary Science: Bright Ideas PB4 A-W 119 6. A complex machine is: (a) a machine made from two or more simple machines (b) a machine that increases a force (c) a machine that increases a distance (d) a machine that is difficult to operate 7. Which of the following is a complex machine? (a) axe (b) nutcrackers (c) rowing boat (d) bicycle 8. Your arm works as a lever. Your biceps muscle supplies the: (a) (b) effort (c) (d) joint 9. Which lever could you use to lift the biggest? (a) (b) (c) (d) effort effort effort effort 10. Which machine can be used to hold on a bottle top, lift a car from the ground and drill a hole? (a) pulley (b) lever (c) screw (d) gear 73