Light Pushes

Radiation pressure and solar sails

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

• Light carries momentum: pressure $I/c$ when absorbed, $2I/c$ when reflected.
• Sunlight near Earth pushes a mirror with about 9 µPa.
• Solar sails use this tiny but endless push.

Steps

1. Momentum without mass
2. Sunlight’s push
3. One photon’s push
4. Optical tweezers
5. Size a solar sail
6. Sailing on sunlight