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Energy
Energy is the ability to make things happen. It changes form — height into speed, motion into heat — but it doesn't disappear.
Roller-coaster energy
kineticpotential
Start height16 m
Speed
0.0 m/s
Kinetic
0.0 J
Potential
158.3 J
Total
158.3 J
t = 0.0 s · m = 2 kg
Two kinds you'll meet first
- Kinetic — energy of motion.
KE = ½ · m · v². Double the speed → four times the energy. - Potential — stored energy. Up high in gravity:
PE = m · g · h.
Conservation
As the coaster rolls, kinetic + potential stays the same. Height becomes speed, speed becomes height. Energy isn't created or destroyed — it just moves around.
Work and power
- Work — force × distance. Pushing harder or further does more work.
- Power — work per second. Watts = joules per second. A 100-W bulb uses 100 J every second.
Other forms
Heat, light, sound, chemical, electrical, nuclear — every kind of energy can be converted into another. A hairdryer turns electrical into kinetic (the fan), heat (the coil) and sound (the noise).