Nature of Work Done

Physics

definition

Condition for Positive, Negative & Zero work done by a force

We know that:

Sign of work done depends on the angle between force and displacement vector.
If - Work done is positive.
If - Work done is zero.
If - Work done is negative.

definition

Positive, Negative and Zero work done

1. Positive Work : If a force displaces the object in its direction, then the work done is positive. The example of this kind of work done is motion of ball falling towards ground where displacement of ball is in the direction of force of gravity.

2. Negative Work : I
f the force and the displacement are in opposite directions, then the work is said to be negative. For example if a ball is thrown in upwards direction, its displacement would be in upwards direction but the force due to earths gravity is in the downward direction.

3. Zero Work : If the directions of force and the displacement are perpendicular to each other, the work done by the force on the object is zero.
For example, when we push hard against a wall, the force we are exerting on the wall does no work, because in this case the displacement of the wall is d = 0. However, in this process, our muscles are using our internal energy and as a result we get tired.

definition

Sign convention

Work done by the system i.e. work done by the gas is positive. Example: expansion of gas on heating. Work done on the system is negative. Example: A constant force being applied on the piston of a cylinder.

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