# Thermodynamics (conceptual)

1. Aug 6, 2010

### Tush

Ques 1) If two bodies are in thermal equilibrium in one frame, will they be in thermal equilibrium in all frames ?

Ques 2) Does the temperature of a body depends on the frame from which it is observed ?

Ques 3) The length of a brass rod is found to be smaller on a hot summer day than on a cold winter day as measured by the same aluminium scale. Do we conclude that brass shrinks on heating ?

Ques 4) If an automobile engine is overheated, it is cooled by putting water on it. It is advised that the water should be put slowly with engine running. Explain the reason.

Ques 5) Is it possible for two bodies to be in thermal equilibrium , if they are not in contact ?

2. Aug 6, 2010

### zhermes

People aren't going to answer a set of homework (or whatever) questions for you.
What specific issues/questions do you have?
What are your thoughts so far?

3. Aug 7, 2010

### Tush

I am really sorry, but these aren't a set of homework questions. I just want a fruitful discussion on these questions.

Now, regarding Ques 3, my doubt is that inspite of positive value of coefficient of linear expansion, then how can the length of brass rod be decreased ? Is it due to the fact that the length of the brass rod is measured on Aluminium scale ? (Coeff of thermal expansion of Aluminium > that of brass).

Now, my point of view about ques 4...... water has the highest specific heat capacity as compared to other substance, so water is used as a coolant in car engines.
Now, Q = m c (dT) where c is the specific heat capacity
"It is advised that the water should be put slowly with engine running" Is it bcoz of the fact that water has highest specific heat capacity as compared to other substance and consequently, more heat is released ???

Last edited: Aug 7, 2010
4. Aug 7, 2010

### zhermes

Question 2 and 5 will help answer question 1. What does thermal equilibrium mean? How is it achieved?

What you said about q3 is I think the only possible solution.

q4: I think you have the right idea. You should add the water slowly w/ the engine running so you don't cool the engine too fast and crack the block. (In actuality one should add water slowly with the engine off--> as soon as an engine starts to over heat it should be turned off).

5. Aug 9, 2010

hhmm thanx

6. Aug 9, 2010

### Andy Resnick

A5 is 'yes', unless you have a strange definition of 'contact'- two bodies may exchange energy by radiation.

A1 and A2 are, I think, 'no' and 'yes'.

http://en.wikipedia.org/wiki/Unruh_effect

7. Aug 9, 2010

### zhermes

I was thinking about that:if they're both in equilibrium in one reference frame, wouldn't any transformation to another reference frame keep them in equilibrium?