4th Class Science Force, Work and Energy Work, Force and Energy

LEARNING OBJECTIVES

This lesson will help you to:—

• understand the concept of work and motion.
• study about force and its application.
• examine how and where energy is used.

Misconcept/Concept

Misconcept: Work is any activity one gets tired doing, gets paid for doing, or doesn’t like doing.

Concept: When a force moves an object through a distance, then work is said to be done.

Amazing Facts

Only 10% of energy in a light bulb is used to create light.

Ninety percent of a light bulb’s energy creates heat.

Compact fluorescent light bulbs (CFLS), on the other hand, use about 80% less electricity than conventional bulbs and last up to 12 times as long.

QUICK CONCEPT REVIEW

Before starting with the topic, you should be aware of two concepts, which are:

Rest: When an object is not moving it is called at rest. Like the table in your room is not moving, it is at rest.

Motion: When an object is changing position, it is said to be in motion. For example a moving car or a flying bird.

WORK

When we apply some force to move something and that thing moves then work is said to be done. It does not matter how much the force is applied, if the thing gets displaced from its position work is said to be done. On the other hand if after applying the force the object does not get displaced work is said to be not done.

For example: If we push the wall with great force, the wall does not get displaced. In this case we have not done any work. But if we push a ball very lightly and it starts rolling, the work is said to be done.

FORCE

When we want to move something we either push or pull it at this point we are putting force. By applying force, we can bring a body at rest, or in motion. For example when you kick a ball it comes into motion. You are applying force in your kick.

We can also stop a moving body and bring it to rest by applying force. Like, you can stop a moving ball. So we can

Say:

When we push or pull something we are applying a force on it.                                               

Friction is the force which stops the movement of a body when the body is in contact with surface.

Force moves the objects and friction force stops the object.

Force can also bring some other changes like;

• Force can change the direction of a moving body. For example, when we ploy with the football, different players move the football in different directions with their force.
• Force can change the speed of a moving body. If you kick a moving ball its speed will increase.
• Force con change the shape of a body. If you stretch a rubber band its shape changes, squeezing a plastic water bottle can change its shape.
• It is not necessary that every time the force is applied it will cause movement or change in shape? When we push a wall it does not get displaced. Also there is no change in its shape.

There are many types of forces;

• Animals and human beings use Muscular force.
• The force applied with the help of tools is called Mechanical force and it produces movement.
• Gravitational force: This is the force which is applied by the earth. Due to this force everything is attracted towards the centre of earth.

When we throw a ball upwards the ball again comes down towards the earth because of the gravitational force being exerted by earth on the ball. Have you ever wondered that if something slips from your hand say your book, why does it go downwards and not upwards?    

Historical Preview

Sir Issac Newton was the first one to discover the gravitational force when he saw an apple falling down from a tree. He thought that why did the apple come down after detaching from the tree? And from here the idea of earth pulling the things towards itself came to his mind and the idea o gravitational force came in to being.

Well now you know that it is because of gravitational force.

ENERGY

The ability to do work is called energy. We do different works and for doing them we need energy. Where do we get our energy from? We get the energy from food. Now vehicles also move. Where do they get energy from? They get the energy from the fuel which we put in them.

There are two major types of energy. The energy present in a resting body is the potential energy and the other is the kinetic energy that is present in the objects, which are in motion.

Now let's understand some other types of energy which we get from various sources.

• Light energy: Light is a form of energy. There are many things which give us light energy. For example:

But these all are manmade sources of light. The most important source of energy is from nature and that is sun.

We also get light by burning wood. But it is not preferred as there are many other sources of light available now and moreover it causes air pollution.

• Electrical energy: It is the energy with which we operate our computers, fans, coolers and lights etc. The electrical energy has made our lives very convenient.

How is electricity produced? The electricity is produced using water, burning coal and by wind too.

• Heat energy: Heat is also a form of energy. Heat energy is used to cook food and to boil water. We get heat energy by burning LPG. Wood and coal etc.
• Wind energy: Moving air is called wind. Wind is also a source of energy. Wind mills are used to generate electricity. It is the wind energy only which helps a boat to sail.

• Solar energy: The energy which we get from sun, is called solar energy. Sun gives us two types of, energies. First type of energy is heat energy and the second is light energy. Many appliances have been developed which use solar energy. For example: solar cooker, solar water heater and solar calculator etc. Solar panels store energy in them in day time and use the energy to light the street lamps at night.

• Hydro energy: There is energy in moving water also. It is used to generate electricity. The electricity produced from water is called hydro electricity. Where hydro means water. Large dams are constructed to make electricity.

So we can say that energy is linked to almost everything we do. We do work with energy and can apply force also with energy.