The physics of thermal energy:

Energy: The capacity of a system to do work.

Matter: Composed of atoms and molecules. Always has mass.

Thermodynamic System: Term describing a defined quantity of matter and energy that is relative to another system. Utilizing thermodynamic systems is about practical applications. There is diminishing returns in applying thermodynamics to matter and energy at microscopic levels, although there is the study of quantum thermodynamics.

Selected thermodynamic systems.

Fig.1

• A: Air inside room
• B: Human Being
• C: Computer
• D: Monitor
• E: Desk

Our selection of the systems is relative to the relationships we wish to analyze. Here we are analyzing a few thermodynamic systems inside a room. But if we wish we can zoom out.

If we zoom out we can select a different set of systems for analysis.

Fig.2

• A: Air outside.
• B: House
• C: Land
• D: Lake
• E: Trees/plants

Our selection of systems has changed. Now all the systems in the room of Fig.1 become part of one system - the house.

Thermodynamic System Relationships

Now that we have described our thermodynamic systems, we can discuss the physics of thermal energy within these systems.

Atoms and molecules

Atoms and molecules make up systems. In Fig.1 the human being is (in a dry physical sense), just a jumble of molecules and atoms. All these molecules and atoms are in motion. This motion is the culmination of the constant little movements, wiggles, jiggles, and vibrations of those atoms and molecules that make up this human. In describing the capacity of all this atomic and molecular movement to do work, physicists refer to it as thermal energy. Remember, energy is defined as the capacity to do work.

These constant wiggles, jiggles, and vibrations are called translational, rotational, and vibrational movements.

If we move further down the scale, thermal energy is the culmination of the kinetic energy of the movement of the constituent parts of an atom (electrons,protons, and neutrons).

Atoms and moleclues have movement because the constituent parts have movement. When this kinetic energy is transfered to another atom it's called the transfer of thermal energy. When the transfer happens in objects such as from a stove to a pan, it does so over the trillions upon trillions of atoms in those objects.

Why do electrons, protons, and neutrons move?
Well, now we are getting down closer to the mysteries of our universe. Except for the electron, which is a fundamental particle, the proton and neutron are made up of smaller particles called quarks. Quarks have electrical charges. Electrically charged particles produce an electromagnetic force and this force creates interaction with other electrically charged particles. These interactions, along with other fundamental particle movements such as "spin" combine to produce these movements, vibrations, and general active nature of atoms. For a discussion on how temperature affects atoms check out  Absolute Zero

Why do these all these particles have electrical charges anyway?
That information is classified. Just kidding. It's just how things are, the way the universe came together after the big bang. Basically, within just a fraction of a second one force known as the "superforce" split into the four fundamental forces of our universe.:

• Gravitational Force
• Electromagnetic Force
• Strong Force
• Weak Force

Why did the universe come together in this precise manner at the moment of the big bang?. Time to do some research on the big bang theory! It's very deep stuff and many people make a career out of trying to find the answer! If you have any more questions after that it's all just philosophy!