Forces And Energy

Lift a bag of rice onto a shelf and you have just paid a bill. The bag was low down and now it is high up, and the difference between those two situations cost you something real: a force from your arms, moved through a distance. Physics has a single word for what you paid, and it is the same word whether the payer is a muscle, an engine, a stretched spring or a waterfall. That word is work, and the receipt it prints is measured in joules.

This lesson turns that idea into five equations you can put numbers into. You will learn what work really means and why holding something heavy above your head does none of it, how a stretched spring and a raised mass both hold energy in waiting, why a car travelling at twice the speed carries four times the kinetic energy and needs four times the distance to stop, and how power separates a machine that does a job quickly from one that does the same job slowly. Every equation you meet here is printed in the specification's own equation sheet, so the marks are never for reciting them: they are for knowing which one the question wants.