E = mc²

Mass is energy

An interactive lesson with 6 steps, about 5 minutes: you predict, drag and solve, with instant feedback on every answer. It runs in your browser and needs JavaScript.

What you’ll learn

• $E = mc^2$: mass and energy are two forms of the same thing.
• Nuclear reactions convert measurable amounts of mass into energy, and that powers the Sun.
• The total energy $E = \gamma mc^2$ grows without limit as $v \to c$, so nothing with mass reaches c.

Steps

1. Pushing harder
2. Rest energy
3. One gram
4. How the Sun shines
5. When Newton breaks down
6. Hot coffee