# E=mc^2

Posers and Puzzles 14 Jan '04 23:51
1. 14 Jan '04 23:51
in the equation E=mc^2, what units are the E, the m, and the c mesured in?
2. royalchicken
CHAOS GHOST!!!
15 Jan '04 00:00
in the equation E=mc^2, what units are the E, the m, and the c mesured in?
Any, as long as they are consistent.
3. 15 Jan '04 02:211 edit
in the equation E=mc^2, what units are the E, the m, and the c mesured in?
Assuming Metric units:

E would be in J.
m is in Kg.
c is in m/s.

-Ray.
4. 16 Jan '04 05:37
Originally posted by rgoudie
Assuming Metric units:

[b]E
would be in J.
m is in Kg.
c is in m/s.

-Ray.
[/b]
you can do it this way also, if you like cgs and larger numbers:
E in ergs
m in g
c is roughly 3e10 cm/s.

since most people don't reckon energy in either joules or ergs but in kilowatt-hours, we should convert to that to express the answer.

here's a side light:
how much energy (in Kwh) do you get if one gram of mass is converted to energy?
5. StarValleyWy
BentnevolentDictater
18 Jan '04 07:101 edit
in the equation E=mc^2, what units are the E, the m, and the c mesured in?
Space-Time, the logic of which is that &quot;in&quot; defines a system of measure?
6. 28 Jan '04 04:22
Excuse me, although the mass of something has almost absolutely nothing to do at all with the weight. So it would be then therefore illogical to measure mass with grams and kilograms.
7. royalchicken
CHAOS GHOST!!!
28 Jan '04 04:27
Originally posted by Dr Donez
Excuse me, although the mass of something has almost absolutely nothing to do at all with the weight. So it would be then therefore illogical to measure mass with grams and kilograms.
Grams, and kilograms are units of mass. So it is wrong to measure [/i]weight[/i] in those units; weight is a force, which is generally measured in Newtons.
8. 28 Jan '04 04:51
I am well aware of that, and that, however, did rouse my attention. It is to my knowledge that these two units of measurement are constantly being used to measure weight! How that this is wrong, most of the world may not know, and I was simply assuming that those taking part in this conversation were &quot;most of the world&quot;.
9. 28 Jan '04 06:50
Originally posted by Dr Donez
I am well aware of that, and that, however, did rouse my attention. It is to my knowledge that these two units of measurement are constantly being used to measure weight! How that this is wrong, most of the world may not know, and I was simply assuming that those taking part in this conversation were "most of the world".
Yes colloquially weight has ben indicated in terms of grams and kilograms. However scientiifically this is completely incorrect. Mass is measured in grams/kilograms, and weight is measured in Newtons.

Mathematically speaking:

Weight = Mass*gravity

Assuming no other force besides gravity is acting on the body.
10. 28 Jan '04 20:52
That is absolutely correct.
11. 29 Jan '04 15:37
Originally posted by BarefootChessPlayer

here's a side light:
how much energy (in kWh) do you get if one gram of mass is converted to energy?[/b]
i guess no one wanted to tackle this.
since everything we are dealing with is in cgs except kWh, we factor to that plane as follows:

we want to convert 1 g to energy, so we put in 1 for m and, as i said before, c is roughly 3e10 cm/s, so we square that, giving 9e20, times the one gram, producing 9e20 ergs.
converting ergs to joules means dividing by 1e7 (1 m = 100 cm, so 1 m^2 = 1e4 cm^2, and 1 kg = 1000 g), so we have 9e13 joules.
a joule is a watt-second, giving us 9e13 W-seconds.
divide by 1000 to get kWs, and by 3600 (sec per hr) to get kWh, producing 2.5e7 or 25 million kilowatt-hours!! i use a (maybe overestimated) maximum of 2500 kWh a month so that would be enough to power 10000 homes like mine for a month!
now if we could just find a way to do that and harness all the energy, we'd never have to worry about electrical shortages!
12. 25 Jul '04 08:05
Originally posted by BarefootChessPlayer
i guess no one wanted to tackle this.
since everything we are dealing with is in cgs except kWh, we factor to that plane as follows:

we want to convert 1 g to energy, so we put in 1 for [b]m
and, as i said before, c is roughly 3e10 cm/s, so we square that, giving 9e20, times the one gram, producing 9e20 ergs.
converting ergs to jo ...[text shortened]... way to do that and harness all the energy, we'd never have to worry about electrical shortages![/b]
everybody knows this...where's the hassle? mass energy equivalence relation is sort of an identity. it holds in any system of units provided it is consistent. In fact mass can very well be measured in joules..