At a more basic level, thermal energy comes from the movement
of atoms and molecules in matter. It is a form of kinetic energy
produced from the random movements of those molecules. Thermal energy of
a system can be increased or decreased.
When you put your hand over a hot stove you can feel the heat. You are feeling thermal energy in transfer, otherwise known as heat.
The atoms and molecules in the metal of the burner are moving very rapidly because
the electrical energy from the wall outlet has increased the thermal energy in the burner.
We all know what happens when we rub our hands together. Our mechanical energy increases the thermal energy content of the atoms
in our hands and skin. We then feel the consequence of this - heat.
Laws of Thermodynamics
On the left you can see 3 hypothetical thermodynamic systems. I've
labeled system C as air for simplicity and the other systems could be
anything really. We'll pretend they are solid objects though, two pieces
of round iron. One is cold, one is hot. The air we'll make a
temperature the same as system A. Instantaneously we put all three into a
sealed box. Technically the the box now becomes System D but for
simplicity we will leave it out.
By convection and radiation the fast moving atoms of system B impact the
movement of the atoms of the air. So the transfer of thermal energy
begins. As the air "heats up" the faster moving air atoms and molecules
now start hitting the thermodynamic boundary of system B and transfering
that energy (thermal energy). All this will occur spontaneously until
an equilibrium temperature is reached among all 3 systems. What is the
lowest that the equilibrium temperature can be? Can it reach Absolute Zero?
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