4th Class Science Force, Work and Energy

                                                            Force, Work and Energy

Whenever we push or pull an object, we apply force. A force can make an object move, can stop a moving object, can change direction of a moving object and can change the shape of an object.

Types of Force

There are different types of forces:

Muscular Force

It is the force exerted by muscles of our body. For example, lifting a bucket, lifting dumbbells, etc.

A man lifting a dumbbells

Elastic Force

It is the force exerted when an elastic material is stretched. For example, stretching of rubber band.

Stretching of a rubber band

Frictional Force

It is the force exerted by two surfaces on each other in opposite direction when one moves over the other, while they are in contact. For example, while walking on a road frictional force is acting between the road and the sole of our shoe.

Friction, between shoes and floor

Gravitational Force

The force exerted by the centre of the earth which pulls objects towards it. For example, when a ball is thrown in the air, it comes back towards the earth due to gravitational force, an apple falling from a tree, etc.

Falling of an apple due to gravitational force

Electrostatic Force

When we rub a comb through dry hair, the comb gets charged and is able to attract tiny bits paper. The force exerted by charged comb on the bits of paper is called electrostatic force.

Charged hairs exert force on balloon

Work

Work refers to an activity that involves applying force on an object and movement of the object in the direction of the force. For example, if a man lifts a bucket then some work is done. In this case, due to the force applied by the man, the movement of bucket takes place in upward direction.

Simple Machines

The tools which make our work easy are called simple machines. For example, pulley, wheel and axle, lever, inclined plane, etc.

              Pulley                             Inclined plane

Energy

Energy is the capacity or ability to do work. Energy can be of various types.

Mechanical Energy

This is the energy of motion that does some work. For example, wind turns a windmill.

Heat Energy

Heat energy is produced when a fuel is burnt in the air. For example, when coal is burnt in the air, heat energy is produced. Heat energy is used in steam engines, in cooking, etc.

Atomic Energy

The energy obtained by splitting of an atom. This energy can also be used to produce electricity.

Electrical Energy

The energy, we get from electricity, is called electrical energy. We use electrical energy in different ways, for example, we use electrical energy to light our house to watch T.V., for running refrigerator, etc.

Gravitational Energy

This energy is due to the earth's gravitational pull.

Light Energy

Sources of light such as sun, bulb, Tube light give light energy.

Sun is a source of light energy

Sound Energy

Radio, televisions, music systems are sources of sound energy.