Think about the reference frame that makes sense to use when talking about the random KE of the molecules of an object.RubinLicht said:
The frame in which the average velocity is zero, so the jar.Doc Al said:
Right. (Also called the center of mass frame.)RubinLicht said:
Ah thanks, makes much more sense than my friends explanation hahaDoc Al said:
So shouldn't the question state, just to be clear, that the thermometer is moving with the jar?Doc Al said:
Good point.haruspex said:
the question makes no reference to thermometers!haruspex said:
Quite so, but how is the temperature to be measured/defined? My point is that it affects the answer.lychette said:
haruspex said:
The usual view is that temperature is a measure of the thermal energy. Bulk motion does not contribute to that.lychette said:
thankyou for pointing out how wrong I have been.haruspex said:
According to the kinetic theory of gases, the temperature of a gas is directly proportional to the average kinetic energy of its molecules. When a gas is in motion, its molecules are colliding and bouncing off the walls of the container, which increases the average kinetic energy. However, the overall temperature of the gas remains constant because the increased kinetic energy is balanced out by the work done by the gas as it expands against the walls of the container.
The motion of gas molecules contributes to the temperature of the gas through their kinetic energy. The more they move and collide, the higher their average kinetic energy and therefore the higher the temperature of the gas. However, when a gas is in motion, the work done by the gas as it expands against the walls of the container counteracts the increase in kinetic energy, resulting in a constant temperature.
When a gas is compressed or expanded, the temperature does not change significantly. This is because the work done by the gas as it expands or contracts against the container walls is equal to the change in its internal energy, which maintains a constant temperature. However, if the compression or expansion is rapid, there may be a slight change in temperature due to the compression or expansion occurring faster than the heat can dissipate.
When the volume of a gas is decreased, the gas molecules have less space to move around and collide with each other, resulting in a decrease in their average kinetic energy. However, the work done by the gas as it contracts against the container walls balances out this decrease in kinetic energy, resulting in a constant temperature.
The temperature of a moving jar of gas can only increase if there is an external heat source adding energy to the gas. In this case, the work done by the gas as it expands against the walls of the container may not be enough to counteract the increase in kinetic energy, resulting in a net increase in temperature. However, in a closed system without an external heat source, the temperature of the gas will remain constant due to the principles of thermodynamics.