Illustrated Physics
physics, drawn
Theme

The arrow of time

Nearly every law works equally well backwards. Almost nothing else does, and the gap between those facts is thermodynamics.
before23.001-1.00momentum 5.00energy 9.50after20.3314.33momentum 5.00energy 9.50energy survives too — but only because e = 1 Mechanics

Collisions are easier than forces, and momentum is the reason

Nobody knows what happens inside a collision. Momentum conservation makes that ignorance irrelevant, which is the whole trick — and energy, deliberately, is not conserved.

 1010145212032104252521061207458109110number of heads1,024 arrangements in total, all equally likelythe middle has 252 of them Thermodynamics

Entropy is a count, and the arrow of time is arithmetic

Nothing in mechanics prefers a direction. Entropy is not a force pushing things toward disorder — it is the observation that some outcomes have vastly more ways of happening than others.

 123400.511.5volumepressure1234net workhot isothermcold isothermadiabatic steps Thermodynamics

The ceiling on every engine, set before it was designed

There is a maximum efficiency no heat engine can exceed, and it depends on nothing but two temperatures. Not the fuel, not the working substance, not the cleverness of the engineer.

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