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Re: temperature of flowing fluid



Robert B Zannelli asked:
...
the naive
question whether nature would care about ... our
definition of thermal energy and whether a temperature measurement made on an
object in motion relative to an observer would in fact indicate a higher
temperature.

The official answer is that temperature is defined in
(and only in) the rest frame of the fluid. Any skillful
measurement of temperature would take this into account.

Of course, a less-than-skillful measurement might get
any answer you can imagine. If you just take a mercury-
in-glass thermometer and hold it steady in a fast-moving
fluid, there will be all sorts of icky effects having to
do with friction and compressibility as the moving fluid
impinges on the thermometer. The reading on the thermometer
will be only distantly related to the official temperature
of the fluid.

Suggestion: Imagine a swarm of thermometers comoving
with the fluid. Read what they say as they flow past.