Here's why:

* Work in physics is defined as the force applied on an object multiplied by the distance the object moves in the direction of the force.

* Positive work means the force and displacement are in the same direction. This means the force is helping the object move.

* Negative work means the force and displacement are in opposite directions. The force is working against the motion.

Example:

* Positive work: Pushing a box across the floor (force and displacement are in the same direction).

* Negative work: Pushing a box up a hill but it rolls back down (force is upwards, displacement is downwards).

Key takeaway: Work is done when a force causes a displacement. If the force and displacement are in the same direction, the work done is positive.