12: Simple Machines

Q.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)

Q.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 fulcrum on one side and the load on the other side make a lever of the third order.

Q.3. Which machines will you use to do the following work? Write their types.

(a) To remove the lid of a tin.                                                   

Ans: Opener – Lever of the second order.

(b) To lift bricks to the top of a tall building.

Ans: Crane – Complex machine.

(c) To cut vegetable.

Ans: Knife Wedge – Simple machine.

(d) To draw water from a well.

Ans: Pulley – Simple machine

(e) To hold a papad for roasting it.

Ans: A pair of tongs – Lever of the third order.

Q.4. Write the answers to the following questions in your own words. 

(a) What is meant by a simple machine?
Ans: Machines which have only one or two parts and a simple and easy structure are simple machines.

(b)Mention the advantages of using a machine.
Ans: Advantages of using a mahine.

(1) Machines, simple or complex, are used to get more work done in        less time and with less effort.

     (2) Machines are used to do certain tasks more easily.

(c) What is meant by a complex machine?
Ans:

1. Complex machines have many parts which carry out many processes for completing a task.
2. For this purpose the parts are joined to one another.
3. Therefore, these machines are called complex machines.
4. Some of the parts of such complex machines are actually simple machines.
5. The structure of complex machine is complicated.

(d) What is a lever? How is the order of the lever determined?
Ans: Lever is a simple machine made up of 3 parts: Load, effort and fulcrum.

Q.5. Why is this so?

(a) Traveller’s bags have wheels.
Ans: Traveller’s bags have wheels because:-

1. Combination of wheel and axle is a simple machine.
2. When the axle starts rotating due to force applied then the wheel fitted in it also starts rotating.
3. This makes easier for travellers to carry a heavy load.
4. Instead of lifting heavy bag, to drawing it on wheels require less energy. Therefore, traveller’s bags have wheels.

(b) Machines have to be maintained.
Ans: Machines have to be maintained because:-

1. Parts of machines rub against one another when they are used.
2. Soiled, dusty parts create more friction. Some parts are affected by the weather, rust and corrosion.
3. Machines get damaged or become useless due to such wear and tear. Hence to avoid this, machines should be maintained properly to keep them in good working condition.

(c) A bicycle is said to be a complex machine.
Ans: A bicycle is said to be a complex machine because:-

     (1) A bicycle has a complicated structure.

(2) A bicycle has many parts which carry out many processes for completing a task.

     (3) Many parts of a bicycle such as pedals, wheels, axle, handle are

           actually simple machines.

     (4) The parts of a bicycle are joined to one another and make it a     

          Complex machine.

Q.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 and their types:-

1. See – saw: lever of the first order.
   Load – fulcrum – effort.
2. Wheelbarrow: lever of the second order.
   Fulcrum – load – effort.
3. Lemon squeezers: lever of the second order.
   Fulcrum – load – effort.
4. Tongs: lever of the third order.
   Fulcrum – effort – load.