The Speed of Light

The same for everyone

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

• Everyone measures the same speed of light, c ≈ 3 × 10⁸ m/s.
• The laws of physics are the same for all observers moving at constant velocity.
• Velocities combine so that nothing with mass reaches c.

Steps

1. Throw on a train
2. Headlights
3. Einstein’s two postulates (1905)
4. The speed limit
5. Aim the probe
6. Head-on