0

Let's say I took a thermometer and affixed it to the end of a poll. Then I went halfway across a bridge and held the other end of the poll and dipped the thermometer into the middle of a river and just held it there. Then I sent my friend upstream a bit and he walked halfway across a bridge up there and dropped one of those floating thermometers into the river and let it float / drift down the middle of the river toward me.

When the floating thermometer came drifting by me where I had the fixed thermometer I could see both thermometers at the same time. Would they both measure the same water temperature?

(Please allow me to say that the resin that affixed the thermometer to the poll was a perfect insulator. I.e. the thermometer was measuring the water temperature and none of the poll temperature.)

Joe C
  • 214
  • 1
  • 8

3 Answers3

1

Perhaps friction might be at play. The thermometer which moves with the river experiences less friction than that at a fixed position, constantly hit by oncoming water, while the other goes with the flow. Hence, it may be likely that the stationary thermometer may produce a higher reading over time due to the friction it experiences with the water gushing by.

QuIcKmAtHs
  • 3,795
  • 4
  • 19
  • 40
0

a thermometer which drifts with the current (at the same speed) will be stuck measuring the temperature of the same body of fluid surrounding it. the expectation in this case is that its reading will change only very slowly over time. On the other hand, the thermometer which is fixed in position and not drifting with the flow will be sampling a different body of water at each instant of its operation, and will capture changes in the temperature of the flow which the drifting thermometer cannot.

niels nielsen
  • 99,024
0

Temperature is a thermodynamic variable but temperature is also defined with statistical methods on the molecules, in your question water.

temp

Where the velocity is the random velocity of molecules in the fluid. If you take a cup of water at a temperature T and put it on a moving train, the temperature derived statistically will not change .

Higher order effects may make a small difference. For example, the water under the bridge will have higher temperature than the water up river because of the change of potential energy to kinetic energy of the water , whereas the trapped floating box only by conduction will acquire more average molecular kinetic energy.

anna v
  • 236,935