Derivation for Newton's Cooling Law

In summary, the conversation discusses the origins and nature of Newton's cooling law, which is often described as an empirical law. The question is raised whether this law can be derived from first principles, particularly the 2nd law of thermodynamics. The conversation also mentions the difficulty in finding a proof or connection between Newton's law and the 2nd law.
  • #1
SpectraCat
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I was thinking about Newton's cooling law, which was originally derived empirically, and is often described as an empirical law. Usually when something is defined as a physical law, it means that it is derived from observation of the world around us, and cannot be derived from more fundamental laws or postulates? Is it really true that Newton's cooling "law" is purely observational, and cannot be derived from first principles?

It seems intuitively obvious that Newton's cooling law follows from the 2nd law of thermodynamics. I started trying to prove this, and I think I see how it might be done, although the details look a bit hairy at first glance. Rather than reinvent the wheel, I thought I'd ask if anyone knows of a reference that gives such a proof ... or one that shows such a proof is impossible. I poked around on google for a while, but I couldn't find anything that looked like what I wanted.
 
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  • #2
The wikipedia article on heat transfer is a good start -- and also mentions why this is an empirical law. It most certainly is not a physical law.
 
  • #3
D H said:
The wikipedia article on heat transfer is a good start -- and also mentions why this is an empirical law. It most certainly is not a physical law.

Yes, I have read that .. and the one on conduction as well. They are quite informative, but not really what I am looking for, because they don't appear to even try to make a connection between the empirical phenomena discussed and the 2nd law. What I would really like to see is a derivation of either Netwon's Law or Fourier's Law (probably easier), starting from the second law and working forward. Lacking that a backward-looking rationalization of these laws that shows the connection to the 2nd LAW (we need different words there for empirical vs. physical laws!) would be my second choice.
 

What is Newton's Cooling Law?

Newton's Cooling Law is a mathematical equation that describes the rate of change of temperature of an object as it cools down or heats up. It states that the rate of change of temperature is proportional to the difference between the object's temperature and the surrounding temperature.

What is the derivation for Newton's Cooling Law?

The derivation for Newton's Cooling Law involves applying the principles of thermodynamics and the laws of heat transfer. It starts with the assumption that the rate of change of temperature is directly proportional to the difference between the object's temperature and the surrounding temperature. This leads to a differential equation which can be solved to obtain the final equation for Newton's Cooling Law.

What are the assumptions made in the derivation of Newton's Cooling Law?

The main assumptions made in the derivation of Newton's Cooling Law include:

  • The object is in a closed system with no external heat sources or sinks
  • The object's temperature is uniform throughout
  • The surrounding temperature remains constant
  • The object's surface area and material properties remain constant
  • The temperature difference between the object and the surrounding is relatively small

How is Newton's Cooling Law used in real-life applications?

Newton's Cooling Law is used in various fields such as engineering, meteorology, and physics to model and predict the cooling or heating of objects. It is used in designing cooling systems for electronic devices, predicting weather patterns, and studying the behavior of materials during phase changes.

Is Newton's Cooling Law applicable to all cooling processes?

No, Newton's Cooling Law is only applicable to cooling processes where the temperature difference is relatively small and the surrounding temperature remains constant. It is not suitable for processes involving phase changes or significant changes in temperature difference.

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