# Calculating e=mc^2 using foot-pounds of force

1. Jun 29, 2013

### markteller

I have seen the on-line calculators, but would like to see how the formula works in full detail. I have seen the kilograms / meters / second example already.

The second part of the question is, what is the actual formula for converting foot pounds of force to Newton meters? Again, the actual details.

Thanks...

Last edited: Jun 29, 2013
2. Jun 29, 2013

### DrewD

What sort of details are you looking for? For the first part, if you just want to calculate the rest energy, then you plug in $m$ and $c$ and get a number. Deriving the formula requires a bit more effort and can be found easily online. If you choose to meters, kilograms, seconds, then you get the energy in Joules. If you want it in ft*lbs then you use the conversion factor. According to the all powerful google, it is $1\ J=0.7375ft\cdot lbs$.

If you wanted to, you could multiply the individual conversion factors to get there. That is, the conversion meters to feet and Newtons to lbs (of force) and get the same number.

3. Jun 30, 2013

### markteller

Thanks!

I am looking to convert 1 kilogram of mass into foot-pounds using e=mc^2 and without any unnecessary conversions. I want to see how the final number is arrived at.

I then want to see how foot-pounds are converted back to newton meters, which are more typical for e=mc^2. Again, I know there are online calculators, but they don't educate the mind :)

4. Jun 30, 2013

### Staff: Mentor

In the spirit of teaching a man how to fish versus simply giving him a fish, it looks like you might benefit from a tutorial on "how to convert units". Here's the first one I found with a Google search on that phrase: