Work is defined as the product of force and displacement in the direction of the force.
* Force: A push or pull that can change an object's motion.
* Displacement: The change in an object's position.
If an object isn't moving, it's not undergoing any displacement. Even if a force is applied, the object's position isn't changing. Since there's no displacement, the work done is zero.
Analogy:
Imagine pushing against a wall. You're applying a force, but the wall doesn't move. You might get tired, but you haven't done any work in the physics sense because there's no displacement.
Example:
* You lift a heavy box. You are doing work because you are applying a force and the box is moving upward.
* You push a car stuck in the mud. If the car doesn't move, you are not doing work (even though you might be expending energy).
Key point: Work is only done when a force causes an object to move in the direction of the force.
