### E=pv and E=pc

Posted:

**Thu Oct 29, 2020 9:52 am**Where did E=pv and E=pc come from? What are they supposed to be? A part of einstein's equation? What is it trying to prove or associate?

Created by Dr. Laurence Lavelle

https://lavelle.chem.ucla.edu/forum/

https://lavelle.chem.ucla.edu/forum/viewtopic.php?f=15&t=65601

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Posted: **Thu Oct 29, 2020 9:52 am**

Where did E=pv and E=pc come from? What are they supposed to be? A part of einstein's equation? What is it trying to prove or associate?

Posted: **Thu Oct 29, 2020 10:32 am**

I don't know a whole lot about these either, but I believe it's just a way to relate momentum and velocity for waves, since we would only use the deBroglie equation (that also relates to momentum) for particles. E=pc is the same as E=pv, but it is just specific to light as the velocity, v, is replaced with the speed of light, c. Again I'm not very well versed on this either so anyone feel free to correct me if I mixed something up!

Posted: **Thu Oct 29, 2020 10:59 am**

I don't know a lot about these either, but I know that they are saying E=mc^2 for objects moving at the speed of light.

Posted: **Thu Oct 29, 2020 11:16 am**

E=pv comes from a simple combination of units. Knowing that E is in J which is kg*m^2/s^2, you can multiply momentum (kg*m/s) by velocity (m/s) to get kg*m^2/s^2.

E=pc comes from knowing the velocity for a photon is the speed of light. So you essentially input C as the velocity for a photon because a photon is a light particle.

Hope this helps!

E=pc comes from knowing the velocity for a photon is the speed of light. So you essentially input C as the velocity for a photon because a photon is a light particle.

Hope this helps!

Posted: **Thu Oct 29, 2020 9:49 pm**

I'm not entirely sure but I think it's a manipulated version of Einstein's equation E = mc^2. You could rewrite this as E = mcc, and since c is the speed of light (velocity constant) you could write it as E = mvv. Since momentum (p) = mass (m) x velocity (v), you could write E = (mv)v as E = pv.

Going back to E = mcc, you could also write this as E = mvc, leaving the second velocity value as c. By substituting p for mv, you would get E = pc.

Hope this helps!

Going back to E = mcc, you could also write this as E = mvc, leaving the second velocity value as c. By substituting p for mv, you would get E = pc.

Hope this helps!

Posted: **Fri Oct 30, 2020 12:07 am**

I believe these are a combination of p=mv and E=h/c

Posted: **Sun Nov 01, 2020 11:57 am**

I think that those equations are derived from E = mc^2 and c = (λ)(v, frequency), P = (m)(v, velocity), and E = (h)(v, frequency)