Radiation Pressure Calculator

What Is Radiation Pressure?

Radiation pressure is the force per unit area exerted by electromagnetic waves. Photons carry momentum, so when light hits a surface it pushes on that surface. The effect is tiny at everyday intensities but significant inside stars and for solar sail spacecraft concepts.

Radiation Pressure Formulas

For a perfectly absorbing (opaque) surface perpendicular to the beam:

$$P = \frac{I}{c}$$

For a perfectly reflecting surface:

$$P = \frac{2I}{c}$$

where $I$ is radiation intensity in W/m² and $c \approx 2.998 \times 10^8$ m/s is the speed of light. Solar intensity at Earth is about 1361 W/m², giving absorbed pressure near 4.5 μPa.

Frequently Asked Questions

Why is reflected pressure twice the absorbed pressure?

A reflecting surface reverses photon momentum, delivering roughly twice the impulse of an absorbing surface that stops photons completely.

What is solar radiation pressure at Earth?

Using the solar constant of about 1361 W/m² on an absorbing surface, pressure is about 4.5 micro pascals (μPa).

Can radiation pressure move objects?

Yes, but only noticeably for very light objects in space. Solar sail missions use large reflective sails to harness this force for propulsion.

Does angle of incidence matter?

Yes. Pressure scales with cos²(α) for a surface tilted at angle α from perpendicular to the beam. This calculator assumes normal incidence.

Why is radiation pressure important in stars?

Inside stars, intense thermal radiation creates outward pressure that balances gravitational collapse, helping maintain stellar equilibrium.

Report

Radiation Pressure Calculator

What Is Radiation Pressure?

Radiation Pressure Formulas

Frequently Asked Questions

Related Tools

Recent Visits