Simple Machines Chapter - Science and Technology STD V PDF

FOR ONLINE USE ONLY DO NOT DUPLICATE Chapter Eleven Simple machines Introduction In Standard Three, you learnt about devices that are used t...

FOR ONLINE USE ONLY DO NOT DUPLICATE Chapter Eleven Simple machines Introduction In Standard Three, you learnt about devices that are used to simplify work. These devices are called simple machines. In this chapter, you LY will learn about some simple machines, for example a lever, an inclined plane and a wedge. You will also learn about three classes of levers and their uses. N O The concept of simple machine Activity 1: Examining the importance of simple machines at work SE Materials: A bottle of soda and a bottle opener Procedure 1. Take the bottle of soda and remove its cap using your hand. What U do you see? 2. Take the bottle opener and remove the cap of the bottle of soda. What do you see? E 3. What will happen to the pupils as they open the bottles of soda in N Figure 1? LI N O R FO Figure 1: Using a bottle opener as a simple machine 171 SCIENCE AND TECHNOLOGY STD V.indd 171 7/30/21 11:04 AM  FOR ONLINE USE ONLY DO NOT DUPLICATE The bottle opener is used to simplify work. In simplifying work, you need special devices. These devices are called machines. Thus, a machine is any device which is used to simplify work. Types of machines There are two types of machines: simple and complex machines. Examples of simple machines are spades, hummers, wheelbarrows, openers, a pair of scissors, seesaws, pulleys, a beam balance, crowbars and spanners. A complex machine is made up of two or more simple machines. Examples LY of complex machines are sewing machines and bicycles. Types of simple machines N There are six types of simple machines: levers, inclined planes, wedges, O wheels and axles, pulleys and screws. Lever SE The lever turns or rotates about a fixed point called a fulcrum or pivot. Its three main parts are the fulcrum or pivot, effort and load. Examples of levers are crowbars, spades, claw hammers, wheelbarrows, U bottle openers, pairs of scissors, spanners and shovels. Classes of lever E There are three classes of lever. N (a) First class lever LI In the first class lever, the fulcrum is between the load and the effort (see Figure 2). Examples include crowbars, pairs of scissors, claw hammers N and the beam balance. Load O Effort R Fulcrum FO 172 SCIENCE AND TECHNOLOGY STD V.indd 172 7/30/21 11:04 AM  FOR ONLINE USE ONLY DO NOT DUPLICATE Effort Load Fulcrum LY N Figure 2: An example of a first class lever O (b) Second class lever In the second class lever, the load is between the effort and the fulcrum, SE as shown in Figure 3. Examples of second class levers are wheelbarrows and bottle openers. Load U Effort Fulcrum E N Effort LI Load N O Fulcrum R FO Figure 3: An example of a second class lever 173 SCIENCE AND TECHNOLOGY STD V.indd 173 7/30/21 11:04 AM  FOR ONLINE USE ONLY DO NOT DUPLICATE Activity 2: Making a second class lever Materials: Nails, wood, a hard box, a saw, a hammer, wire and a wheel Procedure Make a wheelbarrow using the materials listed above. Is the wheelbarrow that you have made a simple machine? Where is the location of the load? LY The wheelbarrow is a second class lever because the load is between the effort and the fulcrum. N (c) Third class lever O In the third class lever, the effort is between the load and the fulcrum, as shown in Figure 4. Examples of third class levers are tongs, brooms, fishing rods, tweezers and shovels. SE Load U Fulcrum Effort E N LI Fulcrum N Effort O Load R FO Figure 4: An example of a third class lever 174 SCIENCE AND TECHNOLOGY STD V.indd 174 7/30/21 11:04 AM  FOR ONLINE USE ONLY DO NOT DUPLICATE Activity 3: Making a third class lever Materials: A catapult rubber, coconut leaf veins or dry grass, a stick of 1.5 m length, two pieces of wood and wire Procedure 1. Tie the coconut leaf veins or dry grass using two pieces of wood and wire. 2. Insert the stick into the coconut leaf veins tied by the pieces of LY wood and wire. 3. Use the catapult rubber to fix the stick into the coconut leaf veins N or dry grass to form a broom (see Figure 5). 4. Clean the environment using the broom you have made. Where O were the load, effort and fulcrum during the cleaning exercise? Fulcrum SE U Effort E N LI Load N O Figure 5: Using a third class lever The cleaning process shown in Figure 5 shows that the upright broom R is a third class lever because the effort is between the fulcrum and the load. FO 175 SCIENCE AND TECHNOLOGY STD V.indd 175 7/30/21 11:04 AM  FOR ONLINE USE ONLY DO NOT DUPLICATE Uses of levers Levers are used to simplify work. For example, when carrying a load from one place to another, you may use a wheelbarrow. When you want to pull out nails from a piece of wood, you use a claw hammer. When cutting hair or clothes, you use a pair of scissors. These are some of the uses of levers in daily life. Exercise 1 Answer the following questions. LY 1. Match each activity in Section A with its corresponding type of lever in Section B N Section A Section B O i. Opening a bottle of soda a. A screwdriver ii. Fishing b. A hoe iii. iv. Screwing a screw Stirring ugali SE c. A spoon d. A knife v. Eating food e. A wooden spoon U vi. Digging the land f. A fishing hook vii. Slicing meat g. A bottle opener E viii. Scooping sand h. A machete N ix. Tightening bolt nuts i. A shovel x. Cutting firewood j. A spanner LI 2. Mention three classes of levers and explain their differences. N 3. Mention three examples of third class levers that are used at home. O 4. List four examples of first class levers. R 5. List three examples of second class levers you have ever used. 6. Draw a diagram of a crowbar and indicate the load, fulcrum and FO effort. 176 SCIENCE AND TECHNOLOGY STD V.indd 176 7/30/21 11:04 AM  FOR ONLINE USE ONLY DO NOT DUPLICATE Inclined plane An inclined plane is a wooden plank or iron bar that is tilted at an angle with one end higher than the other so as to make a slope. This type of simple machine is used to raise or lower objects from elevated places. Examples of inclined planes are a ladder, a ramp, sloping roads and hills, ploughs, chisels and a carpenter’s plane. Inclined planes are used in several places to load and unload cattle or heavy cargo from a truck. Examine Figure 6 and then answer the questions in Exercise 2. LY N O SE U E N LI N O R FO Figure 6: An example of an inclined plane 177 SCIENCE AND TECHNOLOGY STD V.indd 177 7/30/21 11:04 AM  FOR ONLINE USE ONLY DO NOT DUPLICATE Exercise 2 Answer the following questions. 1. Explain the uses of a ladder or an inclined plane. 2. Mention other places where inclined planes are used to simplify work. Wedges LY A wedge is a piece of wood or iron with one end thick and the other end tapering to a thin edge. Have you ever seen an axe? The iron part of the N axe is an example of a wedge, as shown in Figure 7. This simple machine is used to simplify the splitting of timber or firewood. Other examples of O wedges are the sharpened edge of a knife, chisel and the piece of wood or iron with a sharp edge. SE Axe U E Wooden wedge N LI N O R FO Figure 7: Examples of wedges 178 SCIENCE AND TECHNOLOGY STD V.indd 178 7/30/21 11:04 AM  FOR ONLINE USE ONLY DO NOT DUPLICATE Activity 4: Examining how a wedge simplifies work Materials: A wooden or iron wedge, an axe, a log and a mallet or hammer Procedure 1. Take the log and chop it with the axe. 2. Put the wedge into the chopped part of the log and hit it with the LY hammer or the mallet. 3. Continue forcing the wedge into the log by using the hammer. What N do you see? O SE U E N LI N O Figure 8: Uses of wedges R The wooden wedge is used to loosen the tool that gets stuck during the FO chopping of firewood and the splitting of timber or a log. 179 SCIENCE AND TECHNOLOGY STD V.indd 179 7/30/21 11:04 AM  FOR ONLINE USE ONLY DO NOT DUPLICATE Exercise 3 Answer the following questions. Section A: Choose the correct answer. 1. Which part is at the centre in the first class lever? (a) The load (b) The effort LY (c) The fulcrum N 2. Which part is at the centre in the third class lever? (a) The load O (b) The effort (c) The fulcrum SE 3. The following pair is an example of a second class lever: _____. U (a) A bottle opener and a wheelbarrow (b) A shovel and a wheelbarrow E (c) A beam balance and a door N 4. One of the following tools is an example of a wedge: _____. LI (a) A weighing scale beam N (b) A wheelbarrow O (c) A chisel R FO 180 SCIENCE AND TECHNOLOGY STD V.indd 180 7/30/21 11:04 AM  FOR ONLINE USE ONLY DO NOT DUPLICATE 5. Put a tick (√) beside the appropriate class of simple machines that are used to simplify work. No. Device for First Second Third simplifying work class class class i. A wheelbarrow ii. An axe LY iii. A beam balance iv. A shovel v. A crowbar N vi. A pair of scissors O vii. A machete viii. A hoe ix. A broom SE x. A weighing scale U beam 6. Write TRUE for a true statement and FALSE for a false E statement. N (a) A bottle opener is an example of a second class lever. _____________ LI (b) A claw hammer is an example of a third class lever. N _____________ O (c) A beam balance is an example of a first class lever. _____________ R (d) A machine is anything that simplifies work.____________ (e) In the third class lever, the fulcrum is between the load and FO the effort._____________ 181 SCIENCE AND TECHNOLOGY STD V.indd 181 7/30/21 11:04 AM  FOR ONLINE USE ONLY DO NOT DUPLICATE Section B: Answer the following questions. 7. Explain the meaning of a simple machine. 8. Mention six types of simple machines. 9. Mention the main parts of a lever. 10. Explain why an inclined plane is a simple machine. 11. Distinguish between a second class lever and a third class lever. LY 12. Identify and label the parts of a lever indicated by A, B and C, as shown in Figure 9. N O C SE B A U E Figure 9: Uses of charcoal tongs N Vocabulary LI Beam balance a simple machine in which the fulcrum is between N the load and the effort O Lever a simple machine that is divided into three major parts: the load, fulcrum and effort R Simple machine basic machines which are levers, inclined planes, wedges, wheels and axles, pulleys and screws FO Wedge a piece of wood or iron that tapers to a thin edge 182 SCIENCE AND TECHNOLOGY STD V.indd 182 7/30/21 11:04 AM