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Imagine a speck of mass-energy.
The mass of an object comes from the energy
it took to assemble it. According to Einstein's
most famous formula:
Where does the mass of an object come from?
Now, this entire system can be in interaction with
another complete system (this is, of course, how
everything is at our own macroscopic scale)
The mass of an object is NOT
the sum of the masses of its
individual, microscopic parts!
In fact the building blocks of matter (electrons and quarks) have almost no mass at all!
This larger system of systems can
have work done to it by outside forces
in any of the three ways:
Now, we track the entire system
by its center of mass:
Now, imagine a lot of particles
interacting in your system:
If outside forces do work
on the internal particles without changing the center of mass, it goes into the thermal energy (TE) of the system. If the outside forces move the center of mass of this system, the entire system may pick up KE as well.
Imagine a speck of mass with no internal structure:
Now, imagine two specks
of mass interacting:
- It would have no thermal energy (no particles inside to move around)
- It would have no potential energy (no other particles to interact with)
All outside forces can do
is change its motion via work done (W):
Kinetic energy (KE) is the energy of motion
The fundamental interactions are:
- Gravitational
- Electro-Magnetic
- Nuclear
Because of these internal forces, the system has potential energy (PE) (since they can move each other internally).
Now, external forces can change both the particle speeds and their relative positions (which changes their PE)
The various particles inside
the system still have their own
microscopic kinetic and potential
energies, but it's convenient to
call those microscopic
KE and PE's by a new name:
Thermal Energy (TE)
Where E is all the various types of energy inside the system and
c is the speed of light
microscopic KE = temperature energy
microscopic PE = energies of phase changes
Mtotal >> M1 + M2 +M3...
"We shall never cease from exploration
And the end of all our exploring
Will be to arrive where we started
And know the place for the first time."
-T.S. Eliot