About SolveMyPhysics
SolveMyPhysics is a free set of Newtonian mechanics calculators — motion, forces, energy, matter and pressure. It exists because most physics calculators online solve exactly one direction of a formula. You can find the acceleration if you have velocity and time, but not the time if you have velocity and acceleration, even though it is the same equation rearranged.
Every calculator here solves for whichever variable you are missing, accepts the units you actually have, and shows you the rearranged formula it used with your own numbers substituted into it. That last part matters if you are checking homework rather than just collecting an answer.
Everything runs in your browser. Your numbers never leave your device.
Where the constants come from
Nothing here is typed from memory. Standard gravity is exactly 9.80665 m/s² and standard atmosphere exactly 101,325 Pa, both defined constants from NIST CODATA. Unit conversions come from the NIST Guide to the SI: a foot is exactly 0.3048 m, a mile per hour exactly 0.44704 m/s, an avoirdupois pound exactly 0.45359237 kg. Planetary surface gravity comes from NASA's Planetary Fact Sheet.
How each calculator is checked
Every formula lives in one module of pure functions with a regression suite alongside it. The expected values in those tests are worked out independently by hand before the code is run, never generated by calling the function they are meant to verify — otherwise a test only proves the code agrees with itself.
The suite covers ordinary cases, edge cases, and the physically impossible ones. Solving W = F·d·cos θ for force at exactly 90° has no answer, because a force perpendicular to the motion does no work no matter how large it is — so the calculator says so rather than returning a number. Several cross-checks also run between formulas: a mass dropped from a height must arrive with kinetic energy exactly equal to the potential energy it started with, and the site computes both sides live rather than asserting it.
What it deliberately ignores
Air resistance. The free fall and projectile calculators use the standard vacuum equations, which is the usual textbook treatment and is accurate enough for short drops — but a real skydiver reaches a terminal velocity and stops accelerating, and a real golf ball falls well short of its vacuum range. Where that matters, the page says so.