Work in Physics
In physics, "work" is defined as the product of the force applied to an object and the distance the object moves *in the direction of the force*.
The Key: Displacement
The crucial element is displacement. If an object doesn't move at all, or if it moves perpendicular to the direction of the force, no work is done.
Examples
1. Pushing a Wall: You can push against a wall with all your might, but the wall doesn't budge. Even though you're applying a force, you're doing no work because there's no displacement.
2. Carrying a Bag Horizontally: If you carry a heavy bag across a room at a constant speed, you're applying an upward force to counteract gravity. However, the bag is only moving horizontally. Since the force and displacement are perpendicular, you're not doing any work on the bag.
3. Holding a Weight: Holding a weight stationary requires you to exert an upward force to counteract gravity. But since the weight isn't moving, you're not doing any work on it.
Important Note: Even though you're not doing work on the object in these examples, you are still expending energy! Your muscles are contracting, and you're feeling the strain. However, that energy isn't being transferred to the object as work.
Summary
To do work on an object, a force must cause it to move in the direction of the force. If there's no displacement in the direction of the force, no work is done, even if a force is being applied.
