What is energy?
Try to throw a ball up in the air and catch it. What made the ball move through the air? You have energy. This energy moved your arm to exert force on the ball, so the ball moved. You did not see the energy but you saw what it did. It made you move the ball. Because the ball moved, you have done work.
Suppose you continued throwing and catching the ball for an hour, what do you think would happen? Of course you would get tired because you used up the energy stored in your muscles. Without energy,you could not have the force needed to move the ball. You need energy. This is the reason you eat and rest. You need energy to move about and do work.
Kinds of energy
A boy on a skateboard at the edge of the ramp has one kind of energy. A boy on the skateboard rolling down the ramp and up the other side has another kind of energy. How are these two kinds of energy different from each other?
To start a game called skateboarding, a person stands at the edge of the ramp. Only from that position will have enough force to roll down the slope and up to the other side of the ramp. The energy stored in the skateboarder because of the person's position (at the edge of the ramp) is called potential energy. Potential means "having power". The potential or stored energy can be used in the future. Note that all the skateboarder has to do id bend forward and down he goes and up the slope. This time, he has another kind of energy, the energy of motion, called the kinetic energy. The word kinetic comes from the Greek word kinetos, which means "moving".
Potential energy exists in different forms, chemical energy, elastic energy and gravitational potential energy.
Chemical energy is the form of potential energy stored in substances. For example, food, wood and coal have chemical energy. Chemicalenergy can be released through a chemical change. Thus, the chemical energy of food is released by chemical changes including digestion and formation of a high-energy compound that we call ATP. ATP is the immediate source of energy for everything we do. Similarly, the chemical energy of wood or coal is released by burning it. We use this energy for cooking food and for many other purposes.
Strain or elastic energy
Strain or elastic energy is the energy stored in elastic materials such as spring and a strip of rubber. Let's take the example of a "jack-in-the-box". It is a gift box that is intended to surprise the one who receives it. The base of the toy clown is a compressed spring. Opening the box releases the elastic energy of the spring. Another example is a sling shot (a forked stick with a strip of rubber for holding a small stone). The rubber (with stone) is pulled toward the person holding the slingshot. Releasing the stretched rubber releases its elastic energy, hurling the stone to a great distance.
Gravitational potential energy
Gravitational potential energy is the energy possessed by an object because of the pull of gravity. This is the energy possessed by the object as a result of its position. Thus, when you are standing at the top of the stairs, your potential energy is greater than when you are standing closer to the foot of the stairs. If you fall from the top of the stairs, the force of your fall will be greater than if you fall from close to the floor level.
note: originally posted at Exposeknowledge.com under the same author.