Introduction to Thermal Physics

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  • 0:00 What is Thermal Physics?
  • 1:34 Key Areas
  • 3:20 Lesson Summary
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Lesson Transcript
Instructor: David Wood

David has taught Honors Physics, AP Physics, IB Physics and general science courses. He has a Masters in Education, and a Bachelors in Physics.

After watching this lesson you will be able to explain what thermal physics is, as well as the various areas of study and topics that make it up. A short quiz will follow.

What is Thermal Physics?

In a nutshell, thermal physics is the study of heat. Heat energy, or thermal energy, is the energy of a substance or system in terms of the motion or vibrations of its molecules. The faster the molecules in a substance move the more heat energy they have.

If you wanted to know how much thermal energy there was in a glass of water, you would have to total up the energy of all the molecules inside it. Not only is this difficult to do, it isn't entirely helpful. A large glass of cold water has more heat energy than a small glass of cold water, but they feel just as cold. Because of this, we introduce a related term: temperature, which is the average kinetic energy of the molecules in a substance. A large and small glass of water might have the same temperature, even though the large glass of water contains more overall heat energy.

Heat can also transfer, so thermal physics talks about this as well. Touch a metal chair leg, and it feels colder than a wooden desk. But if they're in the same room, and have been there for a while, it's likely that they actually have the same temperature. That's because your hands don't measure temperature; they measure heat transfer. And metals conduct heat particularly fast - the heat in your hand is lost quicker when you touch the metal chair leg, even though the chair leg has the same temperature as the desk. But that's conduction: just one of the types of heat transfer that is studied in thermal physics.

When you begin to study these molecular motions in depth, the topic quickly balloons into a wide variety of areas. So next, we're going to talk about the general areas that collectively make up thermal physics.

Key Areas of Thermal Physics

The key areas of thermal physics we're going to talk about are: thermodynamics, statistical mechanics, and kinetic theory.

Thermodynamics is the study of the movement of heat energy. This encompasses the laws of thermodynamics, which talk about how and why heat moves, the types of heat transfer (conduction, convection and radiation), phase (state) changes, and the relationship between energy and work. Studying thermodynamics also means talking about heat engines - how we can extract useful work using a combination of cold and hot reservoirs.

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