Work

When a force acts on an object and the object shows displacement, the force has done work on the object.

Work = Force × Displacement

Not much work in spite of working hard

• Reading, writing, drawing, thinking, analysing are all energy consuming. But in scientific manner, no work is done in this case.
• A man is completely exhausted in trying to push a rock or wall but work done is zero as wall is stationary.
• A man standing still with heavy suitcase may be tried soon but he does no work in this situation as he is stationary.

Work is said to be done when:-

• a moving object comes to rest.
• an object at rest starts moving.
• velocity of an object changes.
• shape of an object changes.

Scientific conception of work:-

Work is done when a force is applied on a body and when that forces produces motion under its influence.

Condition of work:-

• Force should be applied on the body
• Body should be displaced.

Work is not done when:-

If any one of the above conditions does not exist, work is not done.

Work done by a fixed force:-

y Work done in moving a body is equal to the product of force and displacement of body in the direction of force. Work done by a force acting on an object is equal to the magnitude of the force multiplied by the distance moved in the direction of the force. Work has only magnitude and no direction.

Work = Force × Displcement

W = F × S

Work is a scalar quantity.

SI unit of work is Newton metre or Joule.

When a force of 1 Newton moves a body through a distance of 1metre in its own direction, then the work done is known as 1 Joule.

1 Joule = 1 Newton × 1 metre

1 J = 1 Nm

Factors of work done:-

Work done by a force can be positive, negative or zero.

Positive work:-Work done is positive when a force acts in the direction of motion of the body. (θ = 0^°)

Negative work:-Work done is negative when a force acts opposite to the direction of the body. (θ = 180^°)

Zero work:-Work done is zero when a force acts at right angles to the direction of motion. (θ =90^°)