Temperature increase with stirring?

In summary: If the cup is cold, and the spoon is inserted into the coffee, the contact will cause the coffee to heat up. If the cup is hot, the surrounding air will also heat up, making it harder for the spoon to make a difference.
  • #1
Gabriele Pinna
14
1
Let's say that I have a spoon and a cup of coofee, I stir it with the spoon does its temperature decrease or increase ? (There is friction force so a bit of energy should turn into heat but it's strange).
 
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  • #2
Gabriele Pinna said:
Let's say that I have a spoon and a cup of coofee, I stir it with the spoon does its temperature decrease or increase ? (There is friction force so a bit of energy should turn into heat but it's strange).
What do you think happens? There is a classic experiment where you put energy into the liquid by stirring and measure the starting and finishing temperatures. Have you seen info about that experiment?
 
  • #3
As the macroscopic fluid flow of the stirred coffee diffuses because of internal viscosity and so forth, the energy has to go somewhere, and it does. The large scale motion of clumps of fluid diffuses into small scale molecular motion, which we usually associate with thermal energy.

Assuming all other things constant, the temperature would increase, but by a really tiny amount. It would not be worth trying to heat up coffee by mechanical motion.

2 kilojoules of energy is about what you'd need to heat a glass of water by just 1 degree Celsius.
2 kilojoules of energy is also the amount of kinetic energy in a 4 kilogram bowling ball rolling at highway speeds (100kph)

The amount of kinetic energy in a swirling pot of coffee is a lot less than that of a bowling ball
 
  • #4
I know Joule's experiment but you need to consider that the spoon has a lower temperature than coofee
 
  • #5
In the real world, I would think you would have to stir really fast and furious to keep your coffee warm, and even then it would not help much. Afterall, the coffee is loosing heat through its container, and evaporation, and stirring would help that along. I don't think realistically you could keep up.
 
  • #6
Quantum mechanics is the best way to heat up your coffee. Subject the water molecules to microwave radiation, the increase in rotational energy will warm your coffee just fine. Much better than Joule heating, and no spoon to cool things down, just the cup pulling heat out of the system. (Of course I am being tongue in cheek here.)
 
  • #7
Gabriele Pinna said:
you need to consider that the spoon has a lower temperature than coofee
The answer also will depend on the initial temperatures of the cup and the surrounding air.
 

FAQ: Temperature increase with stirring?

1. What is the relationship between temperature and stirring?

The process of stirring can increase the temperature of a substance by increasing the kinetic energy of its molecules. This is because stirring introduces friction, which generates heat and raises the overall temperature of the substance.

2. How does stirring affect the rate of temperature increase?

Stirring increases the rate of temperature increase by promoting more efficient heat transfer and distribution within the substance. This allows the substance to reach a higher temperature more quickly compared to if it was left unstirred.

3. Can stirring cause a significant temperature increase?

Yes, stirring can cause a significant temperature increase depending on the intensity and duration of the stirring. In some cases, stirring can even be used as a method to control and regulate the temperature of a substance.

4. Are there any other factors that can affect temperature increase with stirring?

Yes, there are other factors that can affect temperature increase with stirring, such as the volume and type of substance being stirred, the speed and direction of stirring, and the type of utensil used for stirring.

5. Is there a limit to how much the temperature can increase with stirring?

Yes, there is a limit to how much the temperature can increase with stirring. This limit is determined by the initial temperature of the substance, the surrounding environment, and the energy input from stirring. Over-stirring may also cause the substance to cool down due to evaporation or heat loss to the surroundings.

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