Physics Calculators

Everyday physics

These tools handle the practical physics that comes up in making, heating, and building — the calculations where you know some quantities and need another, and want to see the formula behind the answer rather than just a number.

The heat energy calculator works out how much energy it takes to warm or cool a material with Q = mcΔT. Thedensity calculator relates mass and volume (ρ = m/V) with a table of common materials, theforce calculator applies Newton's second law (F = ma), and the kinetic energy calculator handles ½mv². Each solves for whichever value you're missing. More physics tools will join this category over time.

Units, and why every page offers both

Every calculator in this category works in SI internally and converts only at the edges — you can type feet, pounds and mph, and the physics still happens in metres, kilograms and seconds before the answer is converted back. That is not cosmetic. Carrying imperial units through a formula is one of the most reliable ways to produce a wrong answer that looks plausible, and keeping conversion at the boundary makes it impossible.

One subtlety worth knowing: a temperature difference is not converted the same way as a temperature. A rise of 180 °F is a rise of 100 °C, not 82.2 °C, because the 32-degree offset applies to absolute readings only. The heat energy calculator handles the two separately for exactly this reason.

Idealised models and where they break

Most of these formulas describe a world without air. Free fall, projectile motion and the pendulum all assume no drag, which is accurate for a dense object over a short distance and increasingly wrong beyond that. A dropped hammer follows the prediction closely; a dropped feather does not, and neither does a skydiver after the first few seconds.

That is why terminal velocityhas its own page. It answers the question free fall deliberately ducks, and it shows something the idealised version hides: with air resistance, mass suddenly matters. In a vacuum a feather and a hammer fall identically. In air they do not, because drag depends on size and shape while weight depends on mass.

Squares are where intuition fails

Several of these relationships scale with the square of a quantity, and that is consistently where estimates go wrong. Kinetic energy and braking distance both scale with speed squared, so going from 50 to 100 km/h does not double the energy or the stopping distance — it quadruples both. Fall time scales with the square root of height, so a drop ten times as high takes only about three times as long. Every page involving a square says so explicitly, because the arithmetic is easy but the intuition is not.