IGCSE 0625 · Section 1.7 · Core

Work is energy on the move.

Whenever a force pushes something along, it does work, and doing work is simply transferring energy. Push twice as hard, or twice as far, and you transfer twice the energy. But push at right angles to the motion and, surprisingly, you do no work at all.

The Key Idea

Work done = force × distance moved in the direction of the force: W = Fd, measured in joules. The work done is equal to the energy transferred. The force must act along the direction of motion for it to do work.

SECTION 01

Force times distance.

Set the pull force, the rope angle, and how far the box moves, then press Pull and watch the energy meter fill. The work done, and the energy transferred, is the force along the floor multiplied by the distance. Increase the force or the distance and the energy rises in proportion. Tilt the rope and watch how only the part of the pull along the motion does any work.

SECTION 02

Only the force along the motion.

A perpendicular force does no work

Work needs the force to act in the direction of the movement. Carrying a bag horizontally at a steady height does no work against gravity, because the upward force is at right angles to the horizontal motion. Multiplying any force by any distance, without checking they are in the same direction, is a common mistake.

Worked Example

A person pushes a crate with a force of 50 N in the direction of motion, moving it 4.0 m across the floor. Find the work done and state the energy transferred.

Step 1 · Apply W = Fd W = F d = 50 × 4.0 = 200 J
Step 2 · Interpret The work done is 200 J, so 200 J of energy is transferred (to the kinetic and thermal stores).
Practice this topic →
Six original Cambridge-style questions.
Calculating work done, work as energy transferred, the no-motion-no-work case, and the perpendicular-force trap. Attempt each, then reveal the worked solution.