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

     Types of Energy

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, which is present in the objects in motion.

         Potential Energy

Potential energy is the energy of an object due to the position of its body. The S.I. unit of potential energy is

When a rubber band is stretched to the left, it exerts a force to the right so as to return to its original un -stretched position. When a mass is lifted up, the force of gravity on the object brings it back to the ground. Roller coaster climbs a hill, it has maximum potential energy at the top of the hill. When the Roller coaster speeds down the hill it starts to loose potential energy.

Kinetic Energy

In simple way, we can say that kinetic energy is the energy of motion. When we walk, run or jump, our body shows kinetic energy. A rubber band flying through the air has kinetic energy. You all must have played with yoyo. How does it work? A yoyo at the rest position has potential energy, at the top has the maximum potential energy. When the yoyo starts to fall, the potential energy begin to change into kinetic energy. At the bottom, its all potential energy has been converted into kinetic energy.

  Yoyo at different position.  

Body showing different types of energy at different position

When an object is dropped from rest from some height above the ground, it has some potential energy but no kinetic energy. As the object starts to fall towards the ground, it losses its potential energy and gains kinetic energy. Just before the object reaches the ground, it has lost all its potential energy and is full of kinetic energy. We all enjoy the view of a water fall. The water comes down from the height to the ground with high speed and the gushing sound. Have you even thought of the type of energy water posses? The water at the top of the hill has stored potential energy. When the water begins to fall, its potential energy is changed into kinetic energy. Kinetic energy can easily be passed from one object to another. Let us see an example to understand it better.

In the game of billiards the players give kinetic energy to the cue ball by striking it with the cue stick. If the ball, which is hit, collides with another ball, it slows down, and the ball it collided with, starts to move. This is because the kinetic energy is passed on to it.

     A brick lying on the roof of a house, which is 10m up from the ground, possess:

(a) Potential energy

(b) Kinetic energy

(c) Heat energy

(d) All of these

(e) None of these

Answer: (a)

    As a ball rolls down on an inclined plane, it has

(a) Only kinetic energy

(b) Only potential energy

(c) Both potential energy and kinetic energy

(d) Has no energy

(e) None of these

Answer: (c)