Radiation Pressure Calculator

Radiation pressure arises from the transfer of momentum from photons to a material boundary. The calculator utilizes two core equations depending on whether you are analyzing external directional light or internal thermal radiation fields. For external sources like sunlight, the pressure is determined by the formula: P = (Surface Type × Solar Constant × cos²(θ)) / (c × 4 × π × d²), where c is the speed of light in a vacuum (approximately 299,792,458 m/s), θ is the angle of incidence, and d is the distance from the source. For enclosed thermal radiation, the internal pressure is computed using the Stefan-Boltzmann radiation constant derivation: P_inside = (4σ / 3c) × T⁴, which simplifies to approximately 7.565767 × 10⁻¹⁶ / 3 × T⁴ based on absolute temperature T in Kelvin.

Imagine you want to calculate the solar radiation pressure experienced by a reflective satellite surface located at a distance of 1 astronomical unit (1.496 × 10¹¹ meters, represented as 1 unit for normalized scaling) from the Sun, where the solar constant is roughly 1361 W/m². Assume the surface is perfectly reflective (surface factor multiplier = 2) and the sunlight strikes perpendicularly at an angle of 0 degrees (cos(0) = 1). Inputting these parameters into the formula yields a tiny yet measurable force. For internal cavity radiation at a stellar core temperature of 10,000 Kelvin, the internal radiation pressure equals approximately 2.52 × 10⁴ Pascals, showcasing how immense temperatures generate significant photon pressure.

Always ensure your temperature inputs are converted to Kelvin before computing internal radiation pressure. When evaluating surface types, remember that a completely absorbing surface has a multiplier of 1, whereas a totally reflective mirror surface doubles the momentum transfer, resulting in a multiplier of 2. Pay close attention to unit consistency, especially when dealing with astronomical distances and standard metric SI units.