The Naked Scientists Forum

Author Topic: What units to find E=MC2?  (Read 2497 times)

krool1969

• Full Member
• Posts: 53
What units to find E=MC2?
« on: 17/11/2011 06:09:25 »
If I wanted to find say how much 1 degree F weighs (in fractions of a gram or ounce?

syhprum

• Neilep Level Member
• Posts: 3821
• Thanked: 19 times
What units to find E=MC2?
« Reply #1 on: 17/11/2011 07:22:52 »
It is energy that you can convert to a mass equivalent with the e=mc^2 formula the temperature which you chosen to express it in F°
IF you heat a Kg of water by 1 F° you add to it 4.18*5/9 (to convert to C°) Joules of energy this equals 2.322 now you can apply the e=mc^2 formula.
The units you use are Mass Kilograms, c meters per second energy Joules, so the mass equivalent of the energy you have added is 2.322/9*10^16 kilograms.

JP

• Neilep Level Member
• Posts: 3366
• Thanked: 2 times
What units to find E=MC2?
« Reply #2 on: 17/11/2011 14:17:48 »
Temperature is an average energy.  The more of a substance you have, the more energy 1 degree means.  The amount of energy needed to raise different materials by one degree also differs.  I get a slightly different answer than syphrum:
2.58*10-17 kilograms of mass-energy per kg water per degree F.

But keep in mind, thats only for 1 kg of water.  Different materials have different values.

Soul Surfer

• Neilep Level Member
• Posts: 3345
• keep banging the rocks together
What units to find E=MC2?
« Reply #3 on: 17/11/2011 15:08:12 »
JP that answer is exactly the same. Its just the way syhprum expressed it as a calculation of energy divided by the speed of light squared

JP

• Neilep Level Member
• Posts: 3366
• Thanked: 2 times
What units to find E=MC2?
« Reply #4 on: 17/11/2011 17:03:11 »
You're right.  For some reason I read the /9 as 5/9.

syhprum

• Neilep Level Member
• Posts: 3821
• Thanked: 19 times
What units to find E=MC2?
« Reply #5 on: 17/11/2011 20:26:08 »
I did not go too deeply into specific heat not wanting to confuse a correspondent brung up on Fahrenheit

Geezer

• Neilep Level Member
• Posts: 8328
• "Vive la résistance!"
What units to find E=MC2?
« Reply #6 on: 17/11/2011 20:53:51 »
to confuse a correspondent brung up on Fahrenheit

I was brung up on Fahrenheit, then they made me learn MKS, and just when I was getting the hang of that they promptly switched over to SI to confuse me even more. Then I moved to another continent and had to go back to Fahrenheit and English units that are no longer used in England. It's really quite straightforward.

EDIT: I forgot that we had to use the CGS system prior to the MKS system. It was good to go to work on an erg.
« Last Edit: 17/11/2011 23:54:40 by Geezer »

krool1969

• Full Member
• Posts: 53
What units to find E=MC2?
« Reply #7 on: 26/11/2011 00:35:11 »
What I'm trying to figure out is how much weight a person loses when they die, assuming the body will cool about 30 degrees.

syhprum

• Neilep Level Member
• Posts: 3821
• Thanked: 19 times
What units to find E=MC2?
« Reply #8 on: 26/11/2011 07:50:24 »
We have already told you that the mass-energy equivalent of one Fahrenheit degree change in temperature in one Kg of water is 2.322/9*10^16 kilograms, assume the specific heat of the body is the same as water and get your calculator out and do the simple arithmetic.
« Last Edit: 26/11/2011 12:43:34 by syhprum »

The Naked Scientists Forum

What units to find E=MC2?
« Reply #8 on: 26/11/2011 07:50:24 »