fifteen formulas · every letter explained beneath it
Built as a memo rather than a table: the thing worth hanging it up for reads across the room, with the full reference in smaller type below it.
Three sizes in one archive — from a sheet on the fridge to a poster on the wall.
Temperature in the gas laws is always taken in kelvin: 0 °C = 273.15 K. The symbols are case-sensitive: V is volume, v is speed.
Kinetic energy grows with the square of speed: E = mv²/2. The brakes must turn all of that energy into heat, while the work done by friction grows only in proportion to the distance covered — so the distance has to grow as a square.
Hence s = v²/(2μg): on dry asphalt 50 km/h gives about 14 m of braking distance, and 100 km/h already about 56 m. The mass of the car does not appear in the formula at all; it cancels from both sides.
And that is only what begins once the pedal is pressed. While the foot travels towards it, the car covers whatever a second of reaction time allows — and that part grows in proportion to speed, not to its square. The two halves of stopping behave differently.
Why the numbers can be trusted. Every countable number here is computed from data rather than typed in, and the sheet must pass 8 independent checks before it is allowed to build — how many items there are, the order they come in, and the claim in the highlighted box itself. If one fails, there is no file.
from the Challenger Deep to the summit of Everest · one scale, nothing compressed
from the first synapsid to us · 320 million years on one axis
when each group appeared · five hundred million years on one axis
the main branches — from comb jellies to chordates · who is actually related to whom