The thermal velocity or thermal speed is a typical velocity of the thermal motion of particles which make up a gas, liquid, etc. Thus, indirectly, thermal velocity is a measure of temperature. Technically speaking it is a measure of the width of the peak in the Maxwell–Boltzmann particle velocity distribution. Note that in the strictest sense thermal velocity is not a velocity, since velocity usually describes a vector rather than simply a scalar speed.
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Since the thermal velocity is only a "typical" velocity, a number of different definitions can be and are used.
Taking
In one dimension
If
If
In three dimensions
If
If
If
By all of these definitions
Thermal Velocity at Room Temperature
At 20 °C (293 Kelvin), the mean thermal velocity of common gasses is:
Molecular Hydrogen 1,754 m/sHelium 1,245 m/sWater vapor 585 m/sNitrogen 470 m/sAir 464 m/sArgon 394 m/sCarbon dioxide 375 m/s