Radiation pressure

Advanced

Light exerts pressure when absorbed or reflected.

Key relationP = I/c

Light exerts pressure P = I/c if absorbed and 2I/c if reflected. At Earth sunlight (1361 W/m²) gives only 4.5 μPa.

Worked example

A 1 km² sail gets about 9 N.

Common mistake

Tiny but constant, so useful in space.

In more detail

Radiation pressure is the pressure exerted when light or other radiation hits a surface and transfers momentum. It is tiny for everyday light but measurable in space and in lab experiments.

Real-world uses

Solar sails and light sails in proposed space missions rely on radiation pressure.
Comet tails are shaped partly by radiation pressure from the Sun.
Comet tails are pushed away from the Sun by radiation pressure, which is the momentum transferred by sunlight.

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Frequently asked questions

Is radiation pressure significant on Earth?

Not for everyday objects, but it can matter for very light objects such as dust.

How is it calculated?

For full absorption, the pressure is intensity divided by the speed of light.

How big is radiation pressure?

It is very small for everyday light, but it matters for tiny particles and for large, light sails in space.

Radiation pressure

In more detail

Real-world uses

Frequently asked questions

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