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# Force, Work and Energy

To do any kind of work we have to apply force and to apply force we need energy. It shows that Work, Force and Energy are related and dependent on each other.

Work                                          Force                                     Energy

Done                                          Applied                                          Needed

We can say that work is done when we possess the energy to apply force.

## Force

Force is a push or a pull acting on an object. Force is used not only to move an object but also stops it. Force is used to change the direction and position of an object. It can be used to increase or decrease the speed of a moving object.

### Types of Force

(i) Frictional force

(ii) Gravitational force

### Friction

Friction is a force exerted when two surfaces are in contact with each other.

• Friction acts on all the moving objects but the direction of the force of friction is always opposite to the direction of movement of the object.
• We need this force of friction in our actions too like walking, running, playing or any other task. If there was no friction we would not be able to walk, play, run or doing any such activities.
• Anything that started to move would never stop without friction.
• Force of friction depends upon the surface of the moving object. Generally, rough surfaces like stoned road, the carpeted floor has more friction as compared to a smooth floor

Gravity

Gravity is the force with which objects are pulled downwards towards the centre of the earth.

## Work

Anything that tires us is known as work like reading, writing, painting, walking, etc. The term 'work' is used equally for both mental and physical work.

• Reading a book or exerting yourself mentally into thinking about a simple or a difficult problem.
• Holding a weight without moving.
• Carrying a load and moving with uniform speed.
• Trying hard to move a huge rock which does not move.

The efforts put in the work exhausts us. Hence, work is said to be done when a constant force is applied to an object which causes the object to move in the same direction as the force is applied.

## Energy

Energy is defined as the capacity to do work.

## Kinetic Energy

A moving object is capable of doing work because of its motion. Therefore, we can say that the object has kinetic energy.

Examples:

• A ball rolling on a surface because it can set another ball into motion by striking it.
• A bullet fired from a gun as it is able to penetrate some distance into a target which it strikes.

### Potential Energy

The energy possessed by an object by virtue of its position is called its potential energy.

### Sources of Energy

The energy which is trapped from any system is called a source of energy. Sun is the ultimate source of almost all energy. Earth receives energy from the sun is in the form of heat and light. Some of the main sources from where we get energy are as follows:

### Different source of Energy

• Solar Energy

The energy that we get from the sun is called solar energy. It is in the form of heat and light. We depend on plants for this process. Thus we can say that all living things are dependent on solar energy directly or indirectly for their energy need.

• Wind Energy

Wind is the movement of air around us. Wind also has energy. The energy of the blowing wind is called wind energy. The energy is due to movement of substances so the energy associated is the kinetic energy.

• Water Energy

Moving water like any moving substance has energy. Many natural processes like weathering of rocks and pebble formation are due to moving water. We use this energy of moving water to produce electricity. Electricity, produced by this process is environment-friendly.

• Energy from the Fossil Fuel

Fossil fuels are the fuel obtained from the remains of plants and animals that got buried inside the earth millions of years ago.

Examples- coal, petrol and natural gas. Fossil fuels are an excellent source of energy for the mankind. They have energy stored in them, which is released by burning them. It is a non-renewable source of energy.

1. What is a force?
2. Define the type of force.
3. What is work?
4. What is energy and what are its type?
5. What are the sources of energy? Describe.

## Recap

• Force is a push or a pull acting on an object.
• Force is used not only to move an object but also stops it.
• Friction acts on all the moving objects but the direction of the force of friction is always opposite to the direction of movement of the object.
• Work is said to be done when a constant force is applied to an object which causes the object to move in the same direction as the force is applied.
• The energy that we get from the sun is called solar energy. It is in the form of heat and light.
• Fossil fuels are an excellent source of energy for the mankind.