Chapter 5 Complex Machines PDF

FOR ONLINE USE ONLY DO NOT DUPLICATE Chapter Five Complex machines Introduction In Standard Six, you learnt about the meaning, types, and applic...

FOR ONLINE USE ONLY DO NOT DUPLICATE Chapter Five Complex machines Introduction In Standard Six, you learnt about the meaning, types, and applications LY of pulleys. You also learnt about the meaning and importance of complex machines. In addition, you learnt about work in science and its applications. In this chapter, you will learn about the structure of N complex machines such as mortise locks, sewing machines, bicycles, grain milling machines, and juice-making machines. You will also O learn about the uses and maintenance of complex machines. The competencies developed will help you to use complex machines to SE simplify work. In addition, you will be able to maintain them properly so that they last longer. U Structure of complex machines Think E Importance of complex machines in daily uses N LI Complex machines are made up of two or more simple machines. These machines simplify work by reducing the amount of force applied and by N changing the direction of the force applied. Therefore, two or more simple machines which form a complex machine are designed to work together. O Examples of complex machines are mortise locks, sewing machines, bicycles, grain milling machines, and juice making machines. R Mortise lock FO The mortise lock is an example of a complex machine, with a key to lock and unlock the door. The mortise lock is a complex machine because it is made up of two or more simple machines. There are different types of mortise locks depending on the need. All mortise locks function similarly. 50 SCIENCE AND TECHNOLOGY STD 7.indd 50 26/07/2021 12:00  FOR ONLINE USE ONLY DO NOT DUPLICATE The structure of the mortise lock The mortise lock is made up of two main parts: the outer part and the inner part. The outer part is made up of a lock handle and a box that covers the lock. The inner part, shown in Figure 1, is made up of simple machines. Hub Latch spring Levers LY Latch bolt Key Deadbolt N O SE Figure 1: Structure of a mortise lock U Those machines are levers, the latch spring, latch bolt and deadbolt. These machines work together during locking and unlocking the door using the key. E N How the mortise lock works The mortise lock has two parts to lock and unlock the door. The first part LI is the one with the handle to hold when closing and opening the door. This part is made up of the latch spring and latch bolt. As you turn the handle N down, the latch spring pulls the latch bolt into the lock and lets the door open. The second part is the one that locks and unlocks the door using O the key. This part works using a lever system and deadbolt. Each mortise lock is unlocked using a specific key. The key has teeth that correspond R to a specific lock. The levers prevent the deadbolt from moving. When you insert the key and rotate it, the lever moves and releases space. The FO space allows the deadbolt to enter or exit the socket on the door casing. The number of levers in a mortise lock is commonly two, three, or five. However, there are mortise locks having one lever. The security of the 51 SCIENCE AND TECHNOLOGY STD 7.indd 51 26/07/2021 12:00  FOR ONLINE USE ONLY DO NOT DUPLICATE mortise lock depends on the number of levers consisting the lock. For example, a mortise lock made of five levers provides more security than the one made of two or three levers. It is easier to duplicate keys for a mortise lock made of one lever or two levers than for a lock made of three or five levers. Activity 1: To examine the structure of the mortise lock and how it works LY Materials: mortise lock, key, and screwdriver Procedure N 1. Unscrew the screws that hold the mortise lock using a screwdriver. 2. Remove the screws slowly and place them in a special place. O 3. Make sure the simple machines inside the mortise lock do not disperse. 4. Observe the parts of the mortise lock that you see. How many simple machines do you see? SE 5. Draw a picture to show the parts of the mortise lock you saw. 6. Insert the key, lock and unlock the mortise lock. Describe what you U saw when locking and unlocking the mortise lock. 7. Assemble the mortise lock as it was before opening it. E Handling the mortise lock The lock needs special care to last longer. Its handling depends on the type N of the mortise lock. Most of the mortise locks are made of iron or copper. LI The outer parts of the mortise lock are cared by wiping them using a clean and dry piece of cloth. Additionally, special oils are used to lubricate the N moving parts of the mortise lock. You must be careful not to bang the door frequently. Banging the door can cause the lock to break after a short O period of use. Exercise 1 R Answer the following questions: FO 1. List simple machines found in a mortise lock. 2. Explain the functions of the simple machines in the mortise lock. 3. Why is the mortise lock grouped as a complex machine? 52 SCIENCE AND TECHNOLOGY STD 7.indd 52 26/07/2021 12:00  FOR ONLINE USE ONLY DO NOT DUPLICATE Sewing machine A sewing machine is used to sew various items such as clothes, shoes, handbags, canvas, and belts. The sewing machine is a complex machine because it is made up of two or more simple machines. There are different types of sewing machines depending on their uses and the sources of energy used by the machine. Some sewing machines are run by feet and others by hand. Other sewing machines use electric energy. Despite their differences, these machines have almost similar structures. In this subsection, you will learn about the treadle sewing machine, which is run by feet. LY The structure of a treadle sewing machine A treadle sewing machine is made up of three main parts, namely the N treadle, pulley, and wheel and axle as shown in Figure 2. The treadle is the O lower part of the sewing Hand wheel machine that receives mechanical force by being Axle pressed by feet. This part is the lever. The pulley is SE Belt the part where there is a U large wheel, called band Band wheel wheel, connected by a belt to a small wheel called E hand wheel. The third part Treadle N is made up of the axle that is attached to the hand LI Figure 2: The structure of a treadle sewing wheel. machine N How the treadle sewing machine works O When the feet work the treadle, a mechanical force that rotates the pulley system is produced. The pulley system consists of two wheels, which are a band wheel and a hand wheel. Both wheels are rotated using a belt. R When the hand wheel rotates, it rotates the axle, causing the needle to drop and rise repeatedly. The sewing machine uses two separate threads: FO one fed from above by the needle and the other fed from below by the bobbin mounted on a shuttle. The needle pushes the thread down through the material, catches the bobbin thread, and pulls it back up through the material. 53 SCIENCE AND TECHNOLOGY STD 7.indd 53 26/07/2021 12:00  FOR ONLINE USE ONLY DO NOT DUPLICATE During sewing, the cloth is moved forward so that the thread on the needle connects the two pieces of the cloth. Activity 2: Study the structure of the sewing machine and how it works Materials: sewing machine, thread, needle and a piece of cloth Procedure LY 1. Look at the parts of the sewing machine. Then, list the types of simple machines that make up the sewing machine. 2. Make sure all the parts are connected properly. N 3. Remove the thread from the needle; push the pedal with your feet; and observe what is happening in the treadle, the band wheel, the O hand wheel, and the needle. Write what you observed. 4. Return the thread to the needle and place the cloth under the needle. SE Then, work the treadle by your feet. Observe whether the piece of cloth is sewn. U Handling a treadle sewing machine For a sewing machine to work properly and last longer, it is important to E keep it free from dust and rust. Thus, it should be covered with a clean cloth when not in use. The threads in use must be carefully stored to N prevent them from letting dust into the sewing machine. The sewing machine has moving parts that need to be lubricated by a special oil. The LI oil lubricates the machine for it to run smoothly. The oil also prevents the sewing machine from getting rusty. It is not advised to use oils other than N the special oil for sewing machines. O Exercise 2 R Answer the following questions: 1. List the types of simple machines that make up a sewing machine. FO 2. Explain what will happen if the sewing machine belt breaks. 3. Why is the sewing machine grouped as a complex machine? 4. Explain what will happen if the sewing machine is not lubricated. 54 SCIENCE AND TECHNOLOGY STD 7.indd 54 26/07/2021 12:00  FOR ONLINE USE ONLY DO NOT DUPLICATE Bicycle A bicycle is a means of transport or exercise. Bicycles can also be used to carry luggage. The bicycle is a complex machine because it is made up of two or more simple machines. These machines work together to enable the bicycle move. There are different types of bicycles. Some bicycles are operated by feet, and others are operated by fuel or electric motor. In this section, you will learn about a bicycle that is operated by feet. LY The structure of a bicycle A bicycle is made up of three types of simple machines. These machines are levers, pulleys, and the wheel and axle. The wheel and axle are at N the front and back wheels. The second machine is the pulley. The pulley O consists of a chain that connects a large gear wheel with pedals and a small gear wheel mounted at the back wheel. The third type is a lever that is made up of two pedals as well as the bicycle brake as shown in Figure 3. SE U Brake Brake E N Front Stand wheel LI Back wheel Pedal Large gear wheel N Small gear wheel Axle Chain O Figure 3: Structure of a bicycle How the bicycle works R When the pedal is rotated, it sends a force to the pulley. The pedal rotates the large gear wheel. This wheel is connected to the small gear wheel FO by a chain. As the chain moves, it drives the small gear wheel. When the small gear wheel rotates, it rotates the back wheel of the bicycle. This condition, in turn, moves the bicycle forward. 55 SCIENCE AND TECHNOLOGY STD 7.indd 55 26/07/2021 12:00  FOR ONLINE USE ONLY DO NOT DUPLICATE Activity 3: Study the structure of the bicycle and how it works Materials: a bicycle Procedure 1. Set the bicycle stand at the back wheel. 2. Rotate the pedals by hand. 3. Observe the pulley system rotated by pedals. (a) What will happen if the chain breaks or falls off? LY (b) What will happen if the axle connecting the pedal breaks? (c) What is the function of the holes in the bicycle chain? N O Handling a bicycle The bicycle will last longer and work effectively if it is regularly inspected and repaired. In addition, cleanliness should be maintained. The bicycle SE must be washed with soap and water whenever it gets dirty. The bicycle has rotating parts that rub each other. Therefore, it is important to lubricate such parts. Lubricants reduce friction, rust and corrosion of the moving U parts. Lubricants are applied to the chain, wheel and axles, and pedals. Lubricants are also applied to the inside of the wheel and axles system since they contain ball bearings. Ball bearings need to be lubricated to E avoid eroding when the bicycle is moving. In addition, make sure that the brakes are working properly to reduce the risk of an accident. N LI Exercise 3 Answer the following questions: N 1. List the simple machines that make a bicycle. O 2. What will happen if the chain is too long? 3. What are the benefits of lubricating the bicycle chain? R Grain milling machine FO Various grains are ground to get flour. This work is done by a grain milling machine. This machine is one of the complex machines. The grain milling machine is made up of two or more simple machines. 56 SCIENCE AND TECHNOLOGY STD 7.indd 56 26/07/2021 12:00  FOR ONLINE USE ONLY DO NOT DUPLICATE The structure of a grain milling machine The grain milling machine is made of an inclined plane called hopper for putting grains, a mill, and a flour outlet. Three types of simple machines compose a grain milling machine. These simple machines are the inclined plane, where grains are poured; the wheel and axle; and the pulley. A mill is made of a wheel and an axle. The wheel and axle are rotated by a pulley. This pulley is made of a wide belt fastened in two wheels. The large wheel is connected to the motor or engine and the small wheel is connected to LY the mill as shown in Figure 4. The grain milling machine can use fuel or electricity. A fuel engine machine converts fuel energy into mechanical energy. Similarly, an electrical motor machine converts electrical energy N into mechanical energy. O Pipe Cloth SE Hopper U E Axle Small wheel N LI Large wheel Belt Axle N Figure 4: The structure of a fuel grain milling machine O How a grain milling machine works R When the machine is turned on, the motor or engine rotates the axle holding the large wheel. When the large wheel rotates, it causes the FO belt to rotate the small wheel, which is attached to the mill. This enables the roller inside the mill to rotate rapidly and grind the grains. The mill is connected to a pipe that draws the flour from the mill. A special cloth is attached to the end of the pipe to prevent the flour from spreading. 57 SCIENCE AND TECHNOLOGY STD 7.indd 57 26/07/2021 12:00  FOR ONLINE USE ONLY DO NOT DUPLICATE Activity 4: To examine the structure of a grain milling machine and how it works Requirement: grain milling machine and electricity Procedure 1. Visit a grain milling machine near the school. 2. Study parts of the machine before it is turned on. 3. Observe how the machine works when it is turned on. LY Handling a grain milling machine N The grain milling machine consists of rotating parts. These parts rub each other and cause a rise in temperature. It is important to check the O temperature of the machine so that it does not exceed the classified limit. If the temperature rises too much, turn off the machine. Check the belt if it is properly tightened. If it is loose, tighten it so that the machine can SE work efficiently. Apply lubricants to all parts that rub each other. Lubricants should be changed at the appropriate time. Make repairs as soon as you find a problem. This is a good strategy to make the machine last longer. U The machine should also be cleaned regularly. Exercise 4 E Answer the following questions: N 1. List the simple machines that make up the grain milling machine. LI 2. Identify the main parts of the grain milling machine. 3. Distinguish the functions of the pulley in the grain milling machine N and in the bicycle. O 4. Explain what will happen if the pulley belt of the grain milling machine breaks. R Juice making machine FO There are various juice processing machines. Example are machines that grind or squeeze fruits such as a blender and fruit squeezer. The blender is a small machine used to make juice. Juice is a beverage produced from fruits, vegetables, or roots. Fruits and vegetables are ground or squeezed, 58 SCIENCE AND TECHNOLOGY STD 7.indd 58 26/07/2021 12:00  FOR ONLINE USE ONLY DO NOT DUPLICATE crushed, and filtered to obtain juice. The blender is one of complex machines. This machine consists of more than one simple machine. The structure of the blender The blender is made of a wheel and axle mounted on the motor. The motor is in the base of the machine and is covered to make it safe for use. The motor converts electrical energy into mechanical energy. The axle is connected to blades. As the axle rotates, it rotates the blades like a fan. LY These parts of the blender are shown in Figure 5 (b). Jug lid N O Jug Blades Axle SE Base, with a motor U Electric plug E (a) Juice machine (b) Parts of the juice machine N Figure 5: Structure of a juice making machine LI How a blender works When the blender is turned on, the motor rotates the axle. The rotating N axle rotates the blades at high speed. The blades grind fruits or vegetables and produce a thick liquid. Some water is added to the liquid. Then, the O mixture is stirred and filtered to obtain juice. R Activity 5: To examine the structure of a blender and how it works FO Requirement: blender and electricity Procedure 1. Take a blender available in your environment. 59 SCIENCE AND TECHNOLOGY STD 7.indd 59 26/07/2021 12:00  FOR ONLINE USE ONLY DO NOT DUPLICATE 2. Remove the jug with blades from the blender’s base. 3. Uncover the lid of the jug and study the blade system of the blender in the jug. 4. Return the jug to the motor and turn on the blender. 5. Observe how the machine rotates and turn it off. Write what you observed. LY Handling the blender Caring for the blender depends on its type and specific instructions. The blender should be cleaned and stored in a safe place after use. It is N cleaned by wiping the base where there is a motor using a piece of cloth and soap. This part should not be immersed in water because water can O damage the motor when it is turned on. Other parts should be opened and washed with soap and water. The jug should be carefully cleaned since its blades are sharp. This part can be cleaned with a soft cloth and rinsed SE with running water. Make sure the blades are dry before putting them back in place. U Exercise 5 Answer all questions in Sections A, B, C and D. E Section A N Choose the most correct answer and write its letter in the box provided. LI 1. Blades are part of the __________. (a) sewing machine N (b) bicycle (c) blender O (d) car wheel 2. The motor in the blender converts electrical energy into__________. R (a) heat energy (b) mechanical energy FO (c) light energy (d) heat and light energy 60 SCIENCE AND TECHNOLOGY STD 7.indd 60 26/07/2021 12:00  FOR ONLINE USE ONLY DO NOT DUPLICATE 3. The force in the grain milling machine is transported from the motor to the mill using the __________. (a) belt (b) wheel and axle (c) levers (d) inclined plane 4. A part that locks or unlocks the door in the mortise lock is made of LY a simple machine called __________. (a) levers (b) spring N (c) screw O (d) wheel and axle 5. The sewing machine is lubricated using __________. (a) grease (b) cooking oil SE (c) special sunflower oil U (d) special oil E Section B Fill in the blanks N 6. To make the sewing machine last longer, it is important to do the LI following: (a) ______________________ N (b) ______________________ O (c) ______________________ (d) ______________________ R 7. Parts of the bicycle that should be lubricated include the following: (a) __________________________ FO (b) __________________________ (c) __________________________ 61 SCIENCE AND TECHNOLOGY STD 7.indd 61 26/07/2021 12:00  FOR ONLINE USE ONLY DO NOT DUPLICATE Section C Write TRUE for a correct statement and FALSE for an incorrect statement in the space provided. 8. Complex machines are made up of more than one simple machine. __________ 9. The mortise lock is a simple machine. __________ 10. Machines often make work very difficult. __________ LY 11. The sewing machine is lubricated with grease. __________ 12. A hopper is a simple machine in a grain milling machine. __________ N Section D O 13. List other complex machines available in your environment. 14. Give the differences between complex machines and simple machines. 15. Describe how the lever, pulley, and wheel and axle work in a bicycle. SE 16. Describe how to care for the mortise lock. U Vocabulary Blades sharp knives mounted on a motor axle in a juice- E making machine Bobbin a metal wheel wrapped with a sewing thread in a N sewing machine LI Treadle a lever worked by the foot and imparting motion to a machine N O R FO 62 SCIENCE AND TECHNOLOGY STD 7.indd 62 26/07/2021 12:00