In a football match it is our common experience to see that when a player kicks a resting ball it moves in a certain direction. Similarly when the goal keeper grabs the ball firmly with his hands it stops moving and remains at rest till it is released again. Do you know why it happens so? In both these actions force is applied on the ball.
Force is a physical quantity which, when applied to a body tries to displace or displaces it. This quantity is equal to the product of the mass of the body and its acceleration. The unit for measuring force is Newton or Dyne. Force is required to set any body in motion and this force is applied in a particular direction. The force is an external agency capable of changing the rest or motion in an object or a body. When force is applied on a body and it gets displaced, we say that work has been done on the body by force. The amount of work done by the force is equal to the product of the force and the distance covered by it. A work done by force is measured in Joules. In short, force is a vector quantity possessing both magnitude and direction.
The capacity of doing work is called energy. Everything in the universe has some energy by which it can do some work. We experience energy in many forms such as mechanical energy, heat energy, light energy, electrical energy, magnetic energy, chemical energy, nuclear energy etc.
Mechanical energy is of two types: potential and kinetic. Potential energy is due to the position of the body while kinetic energy is due to the motion. One form of energy can be converted into the other form of energy. Winding a watch spring stores potential energy. This stored energy gets converted into kinetic energy when the watch starts running. Although energy can be converted from one form to the other, yet the total quantity remains the same.
Some people confuse between power and energy and think of both as the same. But it is not so. Total energy of a body is equal to the capacity of the work done by the body while power is the rate of doing work by the body. It is equal to the amount of work done in unit time. The system to measure unit of power is called horse power (hp) or watt. Horse power is the British unit of power.
One horse power is equal to 735.7 watts. The word ‘watt’ is derived from the International Systems of Unit and named after the British engineer James Watt.
