Physics◆ Rare
Energy conservation
Energiprincipen
Discovered 1847 · Mayer and JouleEUREKA 04
Energy conservation◆
The ideaEnergy never appears or disappears; it only changes form, so the total stays the same.
m·g·h = ½·m·v²
Lets you predictSpeed at the bottom from the height alone.
Tests usually ask
  • Speed of a falling object
  • Where did the energy go?
Scan for the full explanation and a practice question.
Eureka · 04/10
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Physics ◆ Rare: a famous discovery

Energy conservation

Swedish: Energiprincipen · Discovered: Mayer, Joule and Helmholtz, 1840s

Energy never appears or disappears; it only changes form, so the total stays the same.

m·g·h = ½·m·v²

Why it works

Height energy turns into speed energy on the way down, and back again on the way up. Friction turns some of it into heat, but the total is still the same.

The mass cancels out: v = √(2·g·h). A heavy ball and a light ball dropped from the same height reach the same speed, if air resistance is small.

What it lets you predict

Speed at the bottom from the height alone.

How tests ask about it

  • Speed of a falling object
  • Where did the energy go?

Try it

A ball is dropped from 5 m. How fast is it going when it hits the ground? (g = 9.82 m/s²)

Show the answer

v = √(2 · 9.82 · 5) = √98.2 ≈ 9.9 m/s.

Connects to

Newton's second lawOhm's lawPhotosynthesis

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