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💬 Tired but no work?
Push hard against a wall that does not move. You feel exhausted — yet in the scientific sense you may have done no work at all. How?
When is the work done by a force zero?
Work is Zero When
Force is No Force zero (F = 0) displacement perpendicular (s = 0) to displacement
- If the force is zero ( F = 0 ), no work is done.
- If there is no displacement ( s = 0 ), no work is done — e.g. pushing a rigid wall. You feel tired because your muscles use internal energy, but no work is done on the wall.
- If the force is perpendicular to the displacement , the work done by that force is zero (there is no displacement in the direction of the force).
🔹 Ready to Go Beyond
- When a girl carries a box while walking, she pushes up to balance its weight while the box moves horizontally. Force and displacement are perpendicular, so this force does no work on the box.
- In higher grades you will learn how to find the work done when force and displacement are at an angle to each other.
Important Definitions
- Zero force — if the force acting on an object is zero (F = 0), no work is done on it, however far it moves.
- Zero displacement — if there is no displacement (s = 0), the work done is zero however large the force; pushing a rigid wall does no work on it.
- Force perpendicular to the displacement — there is no displacement in the direction of the force , so that force does zero work; carrying a box while walking is an example.
