6. Work, Power & Simple Machines

In science, work has an exact meaning: you do work only when a force moves an object a distance in the direction of the force:
\[ \text{Work} = \text{Force} \times \text{Distance}, \qquad W = F \times d. \]
Work is measured in joules (J). Holding a heavy box still is tiring, but does no scientific work, because nothing moves.

Power is how fast work is done: \( \text{Power} = \dfrac{\text{Work}}{\text{time}} \), measured in watts (W). The same job done faster takes more power.

A simple machine makes work easier by changing the size or direction of a force. The lever, pulley, inclined plane (ramp), wheel and axle, wedge, and screw are the six classic ones.

A machine does not create energy — it lets you use less force over a longer distance to do the same work. Pushing a load up a long ramp takes less force than lifting it straight up, but you push over a greater distance.

⚠️ Common misconception: a machine does not reduce the total work needed. It trades force for distance — the work (force × distance) stays about the same.

💡 Tip: 'work' needs motion. If the distance is zero, the work is zero, no matter how big the force.