When will the work done be positive, negative and zero? State the criteria and also write two examples.

Work is a measure of energy transfer that occurs when an object is moved by a force. The sign of work done can be categorized as positive, negative, or zero based on the direction of the force relative to the movement of the object. Here’s a breakdown of each scenario:

Positive Work

Work is considered positive when the force applied to an object and the direction of the object's movement are in the same direction. This means that energy is being added to the object.

• Example 1: Pushing a box across the floor. If you apply a force to the right and the box moves to the right, the work done is positive.
• Example 2: Lifting a weight straight up. The upward force you exert is in the same direction as the movement of the weight.

Negative Work

Negative work occurs when the force applied to an object is in the opposite direction to the movement of the object. In this case, energy is being taken away from the object.

• Example 1: A car braking. The force of friction acts opposite to the direction of the car's movement, resulting in negative work.
• Example 2: A person lowering a heavy object. The force of gravity pulls down while the object is moved down, leading to negative work.

Zero Work

Work is zero when the force applied does not cause any displacement of the object, or when the force is perpendicular to the direction of movement. In these cases, no energy transfer occurs.

• Example 1: Carrying a bag while walking horizontally. The force you exert upward to hold the bag does not contribute to horizontal movement.
• Example 2: Pushing against a wall. If the wall does not move, the work done is zero, regardless of the force applied.

Understanding these concepts helps clarify how forces interact with objects in various scenarios, influencing energy transfer in physical systems.