Kinetic and potential energy · Year 12
Moving objects have energy in their kinetic store; raised objects have energy in their gravitational potential store. As something falls, energy moves from one store to the other, so we can predict speeds and heights without knowing the forces in detail.
Key facts
- Kinetic energy KE = ½mv².
- Gravitational potential energy ΔGPE = mgh (g = 9.8 N/kg on Earth).
- Doubling speed makes KE four times bigger; doubling mass doubles it.
- With no air resistance or friction: GPE lost = KE gained, so v = √(2gh) (the mass cancels).
- With friction: KE gained = GPE lost − energy wasted.
- Pendulum or roller coaster: use the drop in height between two points.