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Thursday, 17 October 2013

Forces and more forces

This is a short post on forces, Coulombs, Gravitational and Plancks. I will be doing more on this in later posts but this is just a little result that I stumbled upon today. I am certain others have been down this road, but it is a nice result so I thought I would share it with you.

I am not going to go into full detail on how I got this one, it is mostly irrelevant to this post and I will cover it elsewhere. So to start, Planck force is defined as

F_p = \frac {c^4} {G}   ...(1)

c- speed of light
G - gravitational constant

Coulombs force

F_c = \frac {e^2} {4 \pi \epsilon_0 r^2}    ...(2)

e - charge on the electron
1 / 4\pi \epsilon_0 - Coulombs constant
r - distance between the electrons

Gravitational force

F_g = \frac {m_e^2 G} {r^2}    ... (3)

m_e  - mass of the electron
r and G are the same as those above

Dividing (3) by (2) gives

\frac {F_g} {F_c} = \frac {m_e^2 G 4 \pi \epsilon_0} {e^2}    ...(4)

the r term has cancelled here.

Now let's take a look at r_e, the classic electron radius, given by

r_e = \frac {e^2} {4 \pi \epsilon_0 m_e c^2}   ...(5)

We are going to do two things here, the first is to multiple (2) by r_e, while also replacing r with r_e to give

F_c r_e = \frac{e^2 r_e} { 4 \pi \epsilon_0 r_e^2}

we can now cancel the r_e on the right to give

F_c r_e = \frac{e^2} { 4 \pi \epsilon_0 r_e}  ...(6)

now we put (5) into (6) to give

F_c r_e = \frac {e^2 4 \pi \epsilon_0 m_e c^2} { 4 \pi \epsilon_0 e^2}

most of this cancels to leave

F_c r_e = m_e c^2 = E    ...(7)

Secondly put r_e into (2) in place of r and sub in its value from (5) giving

F_c = \frac {e^2 (4 \pi \epsilon_0)^2 m_e^2 c^4} { 4 \pi \epsilon_0 e^4}

after some cancelling this becomes

F_c = \frac { 4 \pi \epsilon_0 m_e^2 c^4} {  e^2} ...(8)

divide this bu F_p to give

\frac {F_c} {F_p} =  \frac { 4 \pi \epsilon_0 m_e^2 c^4 G} {   c ^4 e^2}

cancelling leaves

\frac {F_c} {F_p} =  \frac { 4 \pi \epsilon_0 m_e^2 G} { e^2}    ...(9)

but this is just (4), so

\frac {F_c} {F_p} =  \frac {F_g} {F_c}     ...(10)

so when r = r_e we have

F_c^2 = F_p F_g     ...(11)

Coulomb force squared is equal to the Planck Force multiplied by the gravitational force. Cool eh?

Wrote this while listening to this.

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