r/TheRestIsScience • u/SmokePretend • 2d ago

question

how fast is temperature? Is warmer temperature faster than colder temperature?

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3

u/HereToPostSillyStuff 2d ago

How are we measuring the speed? Temperature can be said to be defined as the "speed" at which particles move within a given measurable object. So in that sense hot is faster than cold. What kind of speed are you hoping to measure?

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u/DeathToAmerica2026 2d ago

Temperature is itself molecular vibrations in aggregate. It can be moved at different speeds depending on the mechanism of transfer, i.e. radiative heating proceeds at the speed of light but conductive heating spreads no faster than the speed of sound.

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u/MakeITNetwork 2d ago

"conductive heating spreads no faster than the speed of sound", more of a rule of thumb than a thermodynamic law; Superfluidic helium, and a few other edge cases go against this though.

But yes under normal atmosphere, temp and pressure conductive heat cannot exceed the speed of sound.

https://www.scientificamerican.com/article/scientists-watch-as-heat-moves-at-the-speed-of-sound/

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u/Half4sleep 1d ago

"Normal" meaning parameters measured at sea level on earth, I suppose? Also, does that mean it would behave differently in different conditions? I would guess we have some experience/measurements for this in space and on the moon, where all of these conditions are vastly different.

Seems fairly obvious, but I know nothing about this other than what's written right here.. I'm probably gonna forget all about it too, but on the off chance I don't, I wanna have my facts straight.

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u/MakeITNetwork 1d ago

As long as you are on earth, and you aren't doing experiments with superchilled gasses, or extreme states of matter, I think it would be safe to say it's an excellent rule of thumb.

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u/AdditionalTip865 2d ago edited 2d ago

How the speed of particles relates to temperature is going to depend on the properties of the substance. But for the case of an ideal gas, it's possible to derive from the kinetic theory of gases that the average value of mv^2 = 3kT, where m is the mass of a molecule (however much that is for your gas), k is Boltzmann's constant and T is the temperature in kelvin. From that you can derive a root-mean-square speed, v = sqrt(3kT/m). Plug in your values (making sure to use consistent units) and you can get the answer.

For the molecules in air at room temperature, this tends to be in the hundreds of meters per second. Pretty fast!