Jump to content

Not really a brainteaser, but oh well


The Thing

Recommended Posts

There are two glasses of water, one is 10 degrees above room temperature, the other 10 degrees below. The water in each glass is identical, glasses are identical, conditions for both glasses of water are identical as well. They are left in a room.

Which glass of water will reach room temperature first? Why?

Link to comment
Share on other sites

  • 4 weeks later...

Fourier's law for conductive heat tranfer states:

q=-k grad T

where q is the heat flux, k is thermal conductivity and grad T is the temperature difference (gradient).

So, in the framework of the approximation provided by this law, the heat flux is equal for both glasses and thus they will reach the room temperature simultaneously.

Link to comment
Share on other sites

  • 3 weeks later...

QUOTE=ecoli]The hotter one should cool down faster, because entropy is favored in the universe. does that make sense?

 

Either that, or it's a trick question, and it happens at the same rate.

 

heat is transfered from hot to cold. the glass of water above room temp. might cool to room temp first. colder water heats up slower.............?

am i off compleatly or is it a trick question?

Link to comment
Share on other sites

  • 1 month later...

The difference between the two situations will be very small. Heat lost/gained by convection will be the same. The only thing that I can see that would change this is the latent heat gained or loss by evaporation or condensation. If the air is dry, then evaporation off both glasses will cause a reduction in temperature resulting in the hot glass reaching equilibrium first. If the air is very humid, then condensation will occur on the glasses, increasing their temperature, so the cold glass will reach equilibrium first.

Link to comment
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now
×
×
  • Create New...

Important Information

We have placed cookies on your device to help make this website better. You can adjust your cookie settings, otherwise we'll assume you're okay to continue.