Introduction
For a layman the term 'work' implies any activity resulting in muscular or mental exertion. In physics, however, the term has a different meaning. It represents a physical quantity.
Work and Measurement of Work
Let us now discuss the conditions to be satisfied for work to be done. From the above examples, it is clear that work is said to be done when a force acts on an object and the point of application of the force moves in the direction of force.
SI Unit of Work
One joule is the work done, when the point of application of a force of one Newton moves through a distance of one meter in the direction of force.
Energy
Any thing, which is able to do work as defined above, possesses energy. We, therefore, define energy as the capacity to do work. Energy is measured by the amount of work that a body can do. Therefore, SI unit of energy is also joule.
Kinetic Energy
It is a matter of common experience that a fast moving stone can break a windowpane, falling water can rotate turbines and moving air can rotate windmills and propel sailboats. In all these examples, the moving body possesses energy. Work is done by the body in motion. This type of energy possessed by moving objects, is known as kinetic energy.
Momentum
We know that all moving objects possess momentum. Momentum of the body is defined as the product of its mass and the velocity.
Potential Energy
Water stored in a reservoir is capable of rotating turbines, which are kept at a lower level i.e, water stored in a reservoir possesses energy.
Law of Conservation of Energy
Steam engine- Here the coal burns and the heat due to the combustion of coal converts water into steam and the expansive force exerted by the steam on the piston of the engine moves the locomotive.
Power
Imagine two students positioned at track A and track B of 100m length shifting 10 bricks from one end of the track to the other end. What is the amount of work done by each one of them? The amount of work done is same but the time taken to perform the work varies. In order to find out the fastest among the two we calculate the work done in unit time. That means work done and work done in unit are two different quantities.
Escape Velocity
All bodies when projected vertically upwards fall back to earth due to the earth's gravitational pull. The maximum height attained by a body depends upon the initial velocity of the body.
Summary
The point of application of force must move in the direction of force.
