the distinction between mechanical and thermal energy is in the mind
The high-school definition of temperature as “a measure of the average kinetic energy of the particles” (see the grandparent comment) actually erases that distinction as it defines temperature through kinetic (mechanical) energy.
Right, but we don’t think of a tennis ball falling in a vacuum as gaining thermal energy or rising in temperature. It is “only” gaining mechanical kinetic energy; a high school student would say that “this is not a thermal energy problem,” even though the ball does have an average kinetic energy (kinetic energy, divided by 1 ball). But if temperature of something that we do think of as hot is just average kinetic energy, then there is a sense in which the entire universe is “not a thermal energy problem.”
but we don’t think of a tennis ball falling in a vacuum as gaining thermal energy or rising in temperature.
That’s because temperature is a characteristic of a multi-particle system. One single particle has energy, a large set of many particles has temperature.
And still speaking of high-school physics, conversion between thermal and kinetic energy is trivially easy and happens all the time around us.
A tennis ball is a multi-particle system; however, all of the particles are accelerating more or less in unison while the ball free-falls. Nonetheless, it isn’t usually considered to be increasing in temperature, because the entropy isn’t increasing much as it falls.
The high-school definition of temperature as “a measure of the average kinetic energy of the particles” (see the grandparent comment) actually erases that distinction as it defines temperature through kinetic (mechanical) energy.
I didn’t read your comment carefully enough. Yes, we agree.
Right, but we don’t think of a tennis ball falling in a vacuum as gaining thermal energy or rising in temperature. It is “only” gaining mechanical kinetic energy; a high school student would say that “this is not a thermal energy problem,” even though the ball does have an average kinetic energy (kinetic energy, divided by 1 ball). But if temperature of something that we do think of as hot is just average kinetic energy, then there is a sense in which the entire universe is “not a thermal energy problem.”
That’s because temperature is a characteristic of a multi-particle system. One single particle has energy, a large set of many particles has temperature.
And still speaking of high-school physics, conversion between thermal and kinetic energy is trivially easy and happens all the time around us.
A tennis ball is a multi-particle system; however, all of the particles are accelerating more or less in unison while the ball free-falls. Nonetheless, it isn’t usually considered to be increasing in temperature, because the entropy isn’t increasing much as it falls.