Chapter 12 - Simple Machines
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.
Ans:
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
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.
Ans: fulcrum, load, effort
(b) The ….. in the centre, the …….. on one side and the ……… on the other side make a lever of the second order.
Ans: load, fulcrum, effort
(c) The ………. in the centre, the ……. on one side and the…….. on the other side make a lever of the third order.
Ans: effort, fulcrum, load
3. Which machines will you use to do the following work? Write their types.
(a) To remove the lid of a tin.
Ans: Can Opener
Type of Machine – Lever
(b) To lift bricks to the top of a tall building.
Ans: Crane
Type of Machine – Pulley
(c) To cut vegetables.
Ans: Knife, cutter
Type of Machine – Wedge
(d) To draw water from a well.
Ans: Wheel, rope
Type of Machine – Lever
(e) To hold a papad for roasting it.
Ans: Pair of Tongs
Type of Machine – Pulley
4. Write the answers to the following questions in your own words.
(a) What is meant by simple machines ?
Ans: Simple Machines are those machines which have only one or two parts and a simple and a easy structure. Examples of simple machines are knife, nutcrackers etc.
(b) Mention the advantages of using a machine.
Ans: The advantages of using a machine are:
(i) More work can be done in lesser time as well as with great accuracy.
(ii) Less effort has to be applied to accomplish the task.
(c) What is meant by complex machines ?
Ans: A machine made up of two or more simple machines is called a complex machine. It consists of different parts that carry out different tasks and together contribute to the working of the machine. The most common example is that of a bicycle.
(d) What is a lever ? How are the orders of the lever determined?
Ans:
A lever is a simple machine having 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 lever 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.
Example: a 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.
Example: a nutcracker, a wheel-barrow, etc.
Lever of third 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.
Example: a nutcracker, a wheelbarrow, etc.
5. Why is this so ?
(a) Traveller’s bags have wheels.
Ans: A traveller’s bag has wheels so that it can be dragged easily because of the reduced friction between the ground and the wheel. Thus, the wheel, a simple machine, helps to decrease the effort to be applied to 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, machines have to be maintained.
(c) A bicycle is said to be a complex machine.
Ans: A bicycle is composed of many simple machines, such as a screw, wheel and axle, lever, and pulley, which carry out different tasks and together contribute to its working. Thus, the 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 meantime, 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:
In the seesaw, we have used the first-order lever. In the first-order lever, the fulcrum is between the load and effort.
In the wheelbarrow, we have used the second-order lever, which means the load is between the fulcrum and effort.
In the lemon squeezer, we have used the second-order lever, which means the load is between the fulcrum and effort.