Definition Of Work
Work is inseperable activity of human life. In physics, work is closely related force that caused body moves. For example, a seller which push his selling cart with his muscular forces, then the cart will move or change from its initial position. It can be said the seller have done work. But if some one push the wall,but the wall keep at rest. That someone is said doesn’t do work.

According to physics, work is defined as the product of force and the displacement in the same direction with that force. Or in other word, the work done by constant force.

Mathematically, work is formulated as follows :
W= F.s

W = work (joule)
F = Force (N)
s = displacement (meter)

in cgs system, work unit is 1 dyne centimeter or equal to 1 erg.


1. Work by one Force
The work done by one force to a body so the body moves in the same direction. Can be formulated as follows :

w= F.s

2. Work by several forces
a. Work by forces in the same direction
The work done by several forces in the same direction to a body so that body moves.

W = F1 . s + F2 . s +F3 . s . . . .
W= W1 + W2 + W3 . . . . . .

b. Work by opposite forces
Resultant of 2 opposite forces is difference of those 2 force. Direction of the force resulltant is direction of the largest force.
W = ( F2 - F1 ).s

With F2 > F1

RELATIONSHIP OF ENERGY AND WORK
The work done can be positive work or negative work. Positive work is the work done by the force in same direction with its displacement, so that body gets addition of energy. Negative work is the work done by force in opposite direction with its displacement,so decrease the energy of that body. So the work done by force that works on a body is equal to the change of kinestic energy of that body.
W = F . s
W = Ek2 – Ek1
W = ½ mv22 - ½ mv12

If the initial height of a body is h1 , then to reach the height to h , from the ground, weight force work for :
W= F. S
W= Ep1 - Ep2
So the magnitude of the work done by weight force on a body is difference of potential energy of body.