Radiation Pressure Calculator
Find the pressure exerted by light on a surface.
Light carries momentum, so it pushes on surfaces it hits — the basis of solar sails.
How the Math Works
Radiation pressure is calculated using the formula P = I ÷ c, where I represents the light's intensity (power per unit area) and c is the speed of light in a vacuum. When light reflects off a surface, the pressure doubles (P = 2I ÷ c) because the photon's momentum changes direction, resulting in twice the force compared to absorption. This relationship stems from the momentum transfer between photons and matter, governed by the conservation of energy and momentum principles in electromagnetism.
Practical Applications
This calculation is critical in designing solar sails for spacecraft propulsion, where maximizing radiation pressure enables efficient movement without fuel. Engineers also use it to assess forces on optical components in precision instruments, such as telescopes or laser systems, ensuring structural stability. Environmental scientists may apply it to model how light interacts with atmospheric particles or ocean surfaces, influencing climate and weather patterns.
Day-to-Day Use
While invisible to the naked eye, radiation pressure affects technologies like solar panels, where even tiny forces can influence energy efficiency over time. It also plays a role in understanding natural phenomena, such as how sunlight drives wind patterns on Earth and other planets. For space enthusiasts, knowing this principle explains why satellites might drift or rotate in orbit, subtly guided by the relentless push of sunlight itself.
Worked example
Sunlight (1361 W/m²) absorbed → about 4.5 µPa.
FAQ
Can it move spacecraft?
Yes — solar sails use this tiny but continuous pressure over large areas.