# Category Archives: Mod Phy

The relation between the sizes of electrons .02 angstroms, Gold Nucleus 10-5 angstroms, and the radius of the atom .5 angstroms.

Very important, we learned about alpha – e^2/4 pi epsilion nought h-bar c, this was called the infinitesimal constant? Didn’t quite catch the name.

So Rutherford was looking at alpha particles, and he was shooting the Helium 4 particles at a thin sheet of gold.

We calculated and equation for knowing the certain number of electrons, which would have their path bent by columbs law and hit at a certain angle of a "ring". To help with this we learned how to calculate solid angles.

Filed under Mod Phy

## Classical Relativity

Classical Relativity
Stars and Planets are in constant motion
And so instead of absolute units we use relative units.

Someone on Earth and someone standing on moving Jupiter watching me run along will see me moving in a different directions. We use coordinates to describe what is the positions Vs time relative to the earth, This can be described using a space time graph, with time on the vertical and position on the horizontal. The line formed by observing this is called the "World Line".

Earth (at Rest)           Jupiter (at v)
t                                    t’
x                                   x’
u                                   u’
a                                   a’
F                                  F’
PE                               PE’
KE                              KE’

The rules of physics are the same in both places, we just need to relate the coordinates.
t’  = t
x’ = x-vt
u  = u-v
F’ = F
a’ = a

Those were the rules until around the 1800’s, but E&M don’t work with this, because once a two charges have velocity, it acquires Magnetic Force, besides the old Electric Force. If you divide the Magnetic force by the Electric force, you are left with the speed of light as the exception. So until your up near the speed of light, this is not much of a problem.
GRAPHIC 1

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