* The force is perpendicular to the displacement: This is the most common scenario. Work is defined as the force applied multiplied by the displacement in the direction of the force. If the force is perpendicular to the displacement, there is no component of the force acting in the direction of motion. Think of carrying a heavy object horizontally: you exert a force upwards to counter gravity, but since you're moving horizontally, that force does no work.
* There is no displacement: If an object doesn't move, no matter how much force is applied, no work is done. A wall being pushed, but not moving, is a good example.
* The object has constant velocity: If an object moves at a constant velocity, the net force acting on it is zero. Since no net force is applied, no work is done. Think of a car moving at a constant speed on a flat road – the engine is doing work to overcome friction, but no net work is being done to accelerate the car.
Examples:
* Pushing a wall: You exert a force, but the wall doesn't move. No work is done.
* Holding a weight at a constant height: You exert an upward force to counter gravity, but the weight doesn't move vertically. No work is done.
* A satellite in orbit: The satellite is moving, but the gravitational force acting on it is perpendicular to its velocity. No work is done by gravity.
Key takeaway: Work is done only when a force causes a displacement in the direction of the force.
