1. Classify the following as a lever, a pulley and an inclined plane :
A wedge, a needle, a staircase, a slide, the wheel of a flagpole, nutcrackers, scissors, an opener, an axe, a crane, a knife.
A wedge: An
A needle: An inclined plane
A staircase: An inclined plane
A slide: An inclined plane
The wheel of a flagpole: A pulley
Nutcrackers: A lever
Scissors: A lever
An opener: A lever
An axe: An inclined plane
A crane: A pulley
A knife: An inclined plane
2. Fill in the blanks using the proper word and complete the statements.
(a) The fulcrum in the centre, the load on one side and the effort on the other side make a lever of the first order.
(b) The load in the centre, the fulcrum on one side and the effort on the other side make a lever of the second order.
(c) The effort in the centre, the load on one side and the fulcrum on the other side make a lever of the third order.
3. Which machines will you use to do the following work? Write their types.
(a) To remove the lid of a tin.
Ans. To remove the lid of a tin, we will use an opener which is a lever of the second order.
(b) To lift bricks to the top of a tall building.
Ans. To lift bricks to the top of a tall building, we will use a crane which is a pulley.
(c) To cut vegetables.
Ans. To cut vegetables, we will use a knife which is a wedge.
(d) To draw water from a well.
Ans. To draw water from a well, we will use a pulley or wheel-axle.
(e) To hold a papad for roasting it.
Ans. To hold a papad for roasting it, we will use a tong which is a lever of the third order.
4. Write the answers to the following questions in your own words.
(a) What is meant by simple machines?
Ans. Machines that have only one or two parts and a simple and easy structure are called simple machines.
(b) Mention the advantages of using a machine.
Ans. Machines help us to get more work done in less time and less effort.
(c) What is meant by complex machines?
Ans. Machines that have many parts joined to one another and carry out many processes for completing a task are called complex machines.
(d) What is a lever? How are the orders of the lever determined?
Ans. A lever is a simple machine which consists of a straight rod that turns at a point called the fulcrum. There are three types of levers depending upon the positions of the effort, the fulcrum and the load.
5. Why is this so?
(a) Traveller’s bags have wheels.
Ans. Traveller’s bag has wheels so that it can be pulled easily because of reduced friction between the ground and the wheel. Thus, the wheel, a simple machine, helps to decrease the effort to be applied on the load which is a bag here.
(b) Machines have to be maintained.
Ans. Parts of machines rub against one another when they are used. Soiled, dusty parts create more friction. Some parts, affected by the weather, rust and erode. Machines get damaged, or become useless due to such wear and tear. To avoid this, it is very important to take care of machines.
(c) A bicycle is said to be a complex machine.
Ans. Complex machines have many parts which carry out many processes for completing a task. A bicycle also has many parts which help the bicycle to move. Therefore a bicycle is said to be a complex machine.
6. Name the levers mentioned in the following passage. Identify the fulcrum, load and effort of each and say which type of lever it is.
Ravi and Savita sit on a sea-saw in a garden. In the mean time, a gardener is trimming trees in the garden. He puts the leaves and other garbage in the wheelbarrow. Later, Ravi gets thirsty and he buys lemon sherbet. The sherbet seller cuts the lemon and squeezes it using a lemon squeezer. He puts small pieces of ice in the glass with the help of the tongs
Ans. Levers mentioned in the passage are:
(a) Sea-saw: It is a first order lever.
(b) Scissors to trim the trees: It is a first order lever
(c) Wheel barrow: It is a second order lever.
(d) Lemon squeezer: It is a second order lever.
(e) Tongs: It is lever of the third order
Fill in the blanks:
1. Devices which are used to get more work done in less time and less effort are called machines.
2. Machines that have only one or two parts and a simple and easy structure are called simple machines.
3. Machines that have many parts which carry out many processes for completing a task are called complex machines.
4. A slanting plank that is used to lift a weight is called an inclined plane.
5. The more gradual the slope of the inclined plane, the lesser is the weight we bear.
6. The steeper the slope of the inclined plane, the greater is the weight we bear.
7. A screw is like a rolled up inclined plane made of an iron strip.
8. The Greek scientist Archimedes invented the Archimedes’ Screw.
9. A sharp tool formed on joining two inclined planes is called a wedge.
10. A wedge in used for breaking an object into two pieces or to seperate objects stuck together.
11. An axe, a knife or a chisel are some examples of a wedge.
12. A needle and a nail are kinds of wedges.
13. A farmer is using a strong crow-bar to remove the big stone bogged down in the farm. Such a machine is called a lever.
14. A lever has three parts, namely, effort, load and fulcrum.
15. The support at which the rod of a lever is rested is called the fulcrum of a lever.
16. The lever rotates about the fulcrum.
17. The weight lifted by a lever or the force against which the lever acts is called the load.
18. The arm of the lever from the fulcrum to the load is called the load arm.
19. The force applied on the other end of the rod to lift the load is called the effort.
20. The part of the lever from the fulcrum to the effort is called the effort arm.
21. As the effort arm becomes longer and longer compared to the load arm, less and less force is required to lift the weight.
22. In the lever of the first order, the fulcrum is in the centre, the load is at one end while the effort is at the other end.
23. In the lever of the second order, the load is in the centre, the fulcrum on one side, and the effort, on the other side.
24. In the lever of the third order, the effort is in the centre, the fulcrum on one side, and the load on the other side.
25. A device with a grooved wheel and thread designed to lift weights is called a pulley.
26. The combination of an axle and a wheel is a simple machine.
27. Some machines are simple while others are complex.
28. The wedge, the lever, the inclined plane, the pulley and the wheel and axle are simple machines.