Conservation of energy?

[Niles]

Hi all.

Lets look at the following scenario: We have an object called A which is kept at 300 K at all times (e.g. a hot plate). Now we have an object B, which is initially 200 K (e.g. a frying pan), and object A and B are now moved together, so they touch eachother.

Of course, object B will now be 300 K as well, and object A is still 300 K.

When I explain this to someone, I would just say that it is intuitively clear that this is how it must be. But can one explain this using conservation of energy, or some other physical law?

I thought about using the first law of thermodynamics: Q = U, but how does one explain that the heat provided by A will make the internal energy of B rise enough, so that the temperature of B is also 300 K?


- Niles.

[thingmaker3]

This might help: http://en.wikipedia.org/wiki/Heat_equation

I'm told by folk more educated than me that there is also a newer equation.

[Niles]

Oh, the heat equation is of course also a possible explanation.

Do you know of any others?

[fanta_hanu]

it can be explained using STEADY STATE ENERGY EQUATION....

[Ratch]

Niles,

Lets look at the following scenario: We have an object called A which is kept at 300 K at all times (e.g. a hot plate). Now we have an object B, which is initially 200 K (e.g. a frying pan), and object A and B are now moved together, so they touch eachother.

It appears to be an event called conduction.

Of course, object B will now be 300 K as well, and object A is still 300 K.

But not immediately. It will take time for the heat energy to propagate throughout the frying pan to bring it up to the temperature of the hot plate.

When I explain this to someone, I would just say that it is intuitively clear that this is how it must be. But can one explain this using conservation of energy, or some other physical law?

You are right. It is intuitive. It is just heat energy moving from one object to another via conduction. Same with heating water in a pot. Ever hear of Fourier's Law of Conduction? http://www.taftan.com/thermodynamics/FOURIER.HTM

I thought about using the first law of thermodynamics: Q = U, but how does one explain that the heat provided by A will make the internal energy of B rise enough, so that the temperature of B is also 300 K?

I don't see why there should be doubt or confusion. Heat transfer through conduction happens constantly everywhere.

Ratch

[studiot]

When I explain this to someone, I would just say that it is intuitively clear that this is how it must be. But can one explain this using conservation of energy, or some other physical law?

You are right to wonder as the First and Second laws of Thermodynamics cannot be derived from more fundamental physical theories. They have just never been observed to be disobeyed.

It has been necessary to introduce something called the Zeroth Law of Thermodynamics to help overcome this.

http://en.wikipedia.org/wiki/Zeroth_...thermodynamics