You do work by spending muscular energy which you gain from the chemical energy of the food you eat. The fan runs on electrical energy. While playing with magnets, you might have seen that a magnet can move a piece of iron so it has magnetic energy.
Thus, energy is available in many different forms like mechanical, thermal, light, electrical, magnetic, sound and nuclear.
This is the capacity of doing work that a body possesses by virtue of its position (potential energy) or by virtue of its motion (kinetic energy).
A body (say hammer) raised to a certain height above the ground when left to itself, falls down. If it is allowed to fall on a piece of dried clay it may break it into pieces. A body raised above the ground has the ability to do work i.e. it has energy. This energy possessed by a body raised above the ground is called its potential energy.
When two bodies one lighter and another heavier are dropped from the same height on a pit of sand, it will be found that the heavier body penetrates more in sand than the lighter body. Hence, a heavier body possesses more potential energy. If same body is dropped from different heights, we find that the body dropped from a greater height penetrates more, hence it has more potential energy.
Potential energy of a body depends on
It is found that the relation between Potential energy PE (Ep), weight (W), and height (h) is
Ep = W × h = mgh
Kinetic energy is the capacity of doing work that a body has by virtue of its motion.
When a body comes down from a height its potential energy decreases where as its kinetic energy increases. The kinetic energy (KE) of a moving body depends on:
It is found that the kinetic energy of a moving body is
KE = ½mv2
This is a form of energy which flows into our body to give us sensation of hotness and out of our body to give us sensation of coldness.
The form of energy which enables us to see things is called light energy.
The energy that lights bulbs, runs fans, operates pumps, heats rooms, turns on TV and runs the refrigerator. The electrical energy is generated due to movement of charged particles.
A magnet can attract a piece of iron. Thus, magnets have an ability to do work. The energy involved in the functioning of a magnet is called magnetic energy.
The form of energy which enables to hear is called sound. Sound originates when a body vibrates giving out waves which travel to our ear through a material medium.
The nuclear energy is a non-conventional form of energy which is released in nuclear reactions by conversion of mass into energy.