Frame dependence of temperature

[Josyulasharma]

Is temperature frame dependent?

The temperature of the system is due to the translational,rotational and vibrational movements of the particles of the system

Now if a box containing gases at a certain temperature is accelerated the molecules in the direction of motion of the gases get more velocity therefore on an average the KE increases this leads to increase in internal energy and finally increase in the temperature.

But I've heard people saying temperature is independent of the frame velocity .
so which is correct??

 

[Bob S]

Suppose a box of ideal mono-atomic gas has reference frame velocities v_xav, v_yav, and v_zav. Then at equilibrium the atoms of the ideal gas have these three average velocities. Now define the rms (root mean square) velocities as

v_{x rms} = sqrt[sum over all atoms (v_x - v_xav)²]/N, et seq. for y and z. where the sums are over N = billions and billions of atoms.

The "thermal temperature" of the gas is given by v_{x rms} et seq, and not by v_xav et seq., and therefore has no direct connection to the reference frame velocity.

 

[Josyulasharma]

Suppose a box of ideal mono-atomic gas has reference frame velocities v_xav, v_yav, and v_zav. Then at equilibrium the atoms of the ideal gas have these three average velocities. Now define the rms (root mean square) velocities as

v_{x rms} = sqrt[sum over all atoms (v_x - v_xav)²]/N, et seq. for y and z. where the sums are over N = billions and billions of atoms.

The "thermal temperature" of the gas is given by v_{x rms} et seq, and not by v_xav et seq., and therefore has no direct connection to the reference frame velocity.

This is strange bob, you see the V_xrmswould not be zero !
because the maxwell - Boltzmann distribution function shows that all the molecules don't go on randomly the momentums of the molecules can be diverse in the x,y,z directions so at any instant the V_x-v_xav^2 would be the sum of all the molecules in the x direction.
Try to relate Consider this 1+1+1+1+...+n/n would not be zero but would not be zero .
but 1
If the one you said was zero
then the rms velocity would have never been before us!

To get it Simple ...
suppose a ball is floating in the mid air in the train.
when the train acclerartes the ball would be fixed to the reference frame of the train.
It would not be just floating in air even if the train moves for an observer outside it would have a pseudo force on it.
anything in the train is always connected to the train!

 

[Bob S]

This is strange bob, you see the V_xrmswould not be zero !
because the maxwell - Boltzmann distribution function shows that all the molecules don't go on randomly the momentums of the molecules can be diverse in the x,y,z directions so at any instant the V_x-v_xav^2 would be the sum of all the molecules in the x direction.

Here is the recipe for calculating the rms molecular velocity distribution about the average velocity on a train. We consider only the x direction, which is the direction the train is moving.
Get a 1 liter box
Count the number of molecules N in it (about 2.7 x 10²²)
(Note: this will take a long time)
Measure the x velocity v_x for each molecule
Add v_x for all N molecules & get sum(v_x)
Calculate average velocity v_av = sum(v_x)/N
For each molecule get mean square deviation from average (v_x-V_av)²
Sum over all N molecules =sum(v_x - V_av)²
Take square root
sqrt{sum(v_x-v_av)²}
Divide by N to get root mean square velocity v_rms
v_rms = [sqrt{sum(v_x-v_av)²}]/N
Does this depend on the velocity v_x of the frame (moving train)?