Here's why:
* Work is defined as the force applied on an object multiplied by the displacement of the object in the direction of the force.
* When the force and displacement are in the same direction, the work done is positive. This means the force is increasing the object's kinetic energy (energy of motion).
* When the force and displacement are in opposite directions, the work done is negative. This means the force is decreasing the object's kinetic energy, slowing it down.
Examples:
* Pushing a box uphill: You are doing positive work because the force you apply is in the same direction as the box's motion.
* Friction: Friction always acts in the opposite direction of motion. It does negative work, converting the object's kinetic energy into heat.
* Braking a car: The brakes apply a force opposite to the car's motion, doing negative work to slow the car down.
Important Note: Negative work doesn't mean the work is "bad" or "useless." It simply indicates that the force is opposing the motion.
