Std 6 th Science- 12. Simple Machines

Question 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.

Answer 1:

A wedge: An inclined plane

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

Question 2:

Fill in the blanks using the proper word and complete the statements.

(a) The ....... in the centre, the .......... on one side and the ...... on the other side make a lever of the first order.

(b) The ..... in the centre, the ........ on one side and the ......... on the other side make a lever of the second order.

(c) The .......... in the centre, the ....... on one side and the........on the other side make a lever of the third order.

Answer 2:

(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.

Question 3:

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

(a) To remove the lid of a tin.

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

(c) To cut vegetables.

(d) To draw water from a well.

(e) To hold a papad for roasting it.

Answer 3:

(a) To remove the lid of a tin, we should use an opener which is a second order lever.

(b) To lift bricks to the top of a tall building, we should use a crane which is a pulley.

(c) To cut vegetables, we should use a knife which is a wedge.

(d) To draw water from a well, we should use a pulley system or wheel-axle.

(e) To hold a papad for roasting it, we should use a tong which is a third order lever.

Question 4:

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

(a) What is meant by simple machines?

(b) Mention the advantages of using a machine.

(c) What is meant by complex machines?

(d) What is a lever ? How are the orders of the lever determined?

Answer 4:

(a) Simple machines are the tools that help people work faster and better. These help us lift heavy loads, change the speed of the motion or the direction of force. Examples are simple machines are knife, nutcrackers etc.

(b) The advantages of using a machine are:

• More work can be done in lesser time as well as with great accuracy
• Less effort has to be applied to accomplish the task

(c) A machine made up of two or more simple machines is called a complex machine. It consists of different parts that carry out different task and together contribute to the working of the machine. The most common example is that of a bicycle.

(d) A lever is a simple machine consisting of a rigid rod which is capable of turning around a pivot called a fulcrum. It has three parts, namely, effort, load and fulcrum.

• Fulcrum: The rod of the lever rests on it and the lever rotates about it.
• Load: The weight lifted by the liver is called the load.
• Effort: The force applied on the other end of the rod to lift the load is called the effort.

The orders of the lever are determined depending on the position of the effort, the fulcrum and the load.

Lever of first order: When the fulcrum is situated between load and effort, we call it a lever of first order. For example, beam balance, a crowbar, a see-saw.

Lever of second order: When the fulcrum and effort are situated at the two opposite ends of the lever and a load is placed in between them, we call it a lever of second order. For example, a nutcracker, a wheel-barrow, etc.

Lever of third order: When the fulcrum and load is situated at the opposite ends of the lever and an effort is applied somewhere between them, we call it a lever of third order. For example, a pair of tongs, a fishing rod, etc.

Question 5:

Why is this so?

(a) Traveller’s bags have wheels.

(b) Machines have to be maintained.

(c) A bicyle is said to be a complex machine.

Answer 5:

(a) Traveller's bag has wheels so that it can be dragged 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) A machine is composed of many parts. These parts rub against one another when in use. Due to this, these parts wear out with time. Also, soil and dust creates more friction between the parts which further deteriorates their condition. Even, some parts get affected by weather and thus rust and erode. Because of these factors, the machine can become useless if proper care is not given to it. So, it is very necessary that we have proper equipments and methods for the maintenance of machines. Thus, machines should be sent for maintenance check at fixed interval of time to ensure their proper working.

(c) A bicycle is composed of many simple machines, such as a screw, wheel and axle, lever, pulley, which carry out different task and together contribute to its working. Thus, the bicycle is said to be a complex machine.

Question 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

Answer 6:

Levers mentioned in the passage are:

(a) Sea-saw: It is a first order lever.

(b) Wheel barrow: It is a second order lever.

(c) Lemon squeezer: It is a second order lever.