Category : 4th Class
This lesson will help you to:—
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.
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.
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.
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
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;
There are many types of forces;
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?
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.
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.
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.
How is electricity produced? The electricity is produced using water, burning coal and by wind too.
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.
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