Snell's Law Calculator

Solve n₁sin θ₁ = n₂sin θ₂ for either angle or either index, get the critical angle, and watch the incident, reflected and refracted rays move on a live diagram — total internal reflection included.

Checking a homework answer, sizing something before building it, and getting an order of magnitude before committing to a design — a torque on a bolt, the force a spring returns, the frequency a circuit resonates at, how long light takes to arrive.

Feeding in a value in the wrong unit. Physics formulas assume SI throughout, so grams instead of kilograms or centimetres instead of metres shifts the answer by powers of ten without any warning.

They sit next to each other but answer different questions. Coulomb's Law Calculator: solve F = kq₁q₂/εᵣr² for the force, either charge or the distance, in any of 18 dielectric media, with charges in C, µC, nC or elementary charges, plus the potential energy and the field at q₂. Pick whichever matches what you're starting from — both are free.

Kepler's Third Law Calculator is the closest one after this: Get the orbital period from T = 2π√(a³/GM) with the semi-major axis in AU, km or solar radii and the central mass in solar, Earth or Jupiter masses — plus orbital speed and the a³/T² constant.

Hooke's law calculator and Spring constant calculator (Hooke's law) — they come up in the same task often enough to be worth a second tab.

Constants are the CODATA values and the formulas are the textbook ones. Most assume an idealised case — no air resistance, no friction, a point mass — and the tool says so where the simplification matters.