I’ve heard this, but then I asked once what speed water molecules in a room temperature glass of water would be going. Are they like walking, driving, flying in a jet, or much faster? I was told my question didn’t have an answer since it didn’t really work that way or something.
I often wondered if the person answering just wasn’t able to make some assumption needed to answer because I didn’t state it in the question, or if saying thermometers measure speed is just wrong.
As mentioned above, there are other ways molecules can jiggle besides the three translational degrees of freedom that imbue substances with their kinetic temperature. As can be seen in the animation at right, molecules are complex objects; they are a population of atoms and thermal agitation can strain their internal chemical bonds in three different ways: via rotation, bond length, and bond angle movements; these are all types of internal degrees of freedom.
tl;dr
Water be jiggly. Amount of jiggle is hard to put a number on
It would still be possible to answer the speed question, you just get different answers for different substances (and even phases of the same substance) at the same temperature.
Since something like water does have those additional ways to store energy, my guess is it would be slower at room temp than another liquid with less complex molecules that have about the same mass each. (If there is such a thing)
Also I expect different answers for each of mean, median, and mode speeds.
So if I were jiggling, I think I could come up with a speed. I’d figure out how far I’m moving, and how long it takes me to move. So I could measure from far left to far right of the jiggle (let’s say 18in.) and then how far to go from far left to far right and return to the original position. If that’s 2 seconds, then that’s 1½ feet per 2 seconds which can be converted to any other speed such as km/hr.
The answer by the thermometer is the temperature, which is based on more degrees of freedom. You’ll have to define some mapping between the other degrees and velocity.
I’ve heard this, but then I asked once what speed water molecules in a room temperature glass of water would be going. Are they like walking, driving, flying in a jet, or much faster? I was told my question didn’t have an answer since it didn’t really work that way or something.
I often wondered if the person answering just wasn’t able to make some assumption needed to answer because I didn’t state it in the question, or if saying thermometers measure speed is just wrong.
See figure 3 here: https://en.m.wikipedia.org/wiki/Thermodynamic_temperature
tl;dr Water be jiggly. Amount of jiggle is hard to put a number on
It would still be possible to answer the speed question, you just get different answers for different substances (and even phases of the same substance) at the same temperature.
Since something like water does have those additional ways to store energy, my guess is it would be slower at room temp than another liquid with less complex molecules that have about the same mass each. (If there is such a thing)
Also I expect different answers for each of mean, median, and mode speeds.
So if I were jiggling, I think I could come up with a speed. I’d figure out how far I’m moving, and how long it takes me to move. So I could measure from far left to far right of the jiggle (let’s say 18in.) and then how far to go from far left to far right and return to the original position. If that’s 2 seconds, then that’s 1½ feet per 2 seconds which can be converted to any other speed such as km/hr.
Show off. 😠
I’m rather jiggly.
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How does the thermometer get its answer? I’d measure that part.
The answer by the thermometer is the temperature, which is based on more degrees of freedom. You’ll have to define some mapping between the other degrees and velocity.