# Homework Help: Question concernig E=MC^2

1. Aug 24, 2005

### whatzzupboy

What do the variables M and C reffer to, in the equastion E=MC^2?

2. Aug 24, 2005

### Concorde

C stands for the speed of light I think and I know M stands for mass.

3. Aug 24, 2005

### Pengwuino

m = relativistic mass of the particle in question
c = the speed of light in a vacuum, ~300,000km/s

Last edited: Aug 24, 2005
4. Aug 24, 2005

### whatzzupboy

i thought the speed of light was 299,292.6Km/S

5. Aug 24, 2005

### irrehaare

i thought that it depend on the environment where is the light, so the velocity of light in air is different than in water or glass . see more about diffraction of light

6. Aug 24, 2005

### whatzzupboy

ok well im basing the equastion out side the universe so... what then is C?

7. Aug 24, 2005

### Pengwuino

C is the speed of light in a vacuum

8. Aug 24, 2005

### Pengwuino

Well the speed of light can change, but as far as the formula goes, you are able to determine the energy based off of its maximum speed i think. Since you can make it so that there's no actual light flying around in an isolated nuclear reaction, theres no speed to base a change in c off of.

9. Aug 24, 2005

### whozum

Outside the universe? Wheres that? Why would there be light there?

10. Aug 24, 2005

### Pengwuino

And what matter would there be "outside the universe"???

11. Aug 25, 2005

### HallsofIvy

You've been told what c is several times now. (And that "out side the universe" makes no sense.)

Did you mean "outside the atmosphere" (i.e. in vacuum) rather than "out side the universe"?

Do you know what "~" means?

12. Aug 26, 2005

### xFlankerx

Owned. But I thought the "C" was the speed of light in meters which would make it ~300,000,000 m/s. What difference does it make? In multipling, you would be multipling by 300,000,000 instead of 300,000.

Last edited: Aug 26, 2005
13. Aug 26, 2005

### quasar987

I suggest you keep you "owned" and "pwned" for yourself. Please.

Btw, I'm not sure I understand your post. When you say "What difference does it make?", are you saking yourself a question and then answering it, or are you really asking that question? Cuz my answer would be: "In so far as every unit system is as good as any other, it makes no difference wheter you take 'c' to be 300,000 km/s, 300,000,000 m/s or 1 M/s, where I have define the lengh 1M to be equivalent to 300,000,000 m (I heard this is what particle physicists use as the unit of lenght in their calculations)

14. Aug 26, 2005

### Pengwuino

C can be done in any length. Heck it can be done in feet or centimeters or earths!

15. Aug 26, 2005

### Dr.Brain

$E=mc^2$ is basically an idea that when 'm' mass is annihilated , a radiation carrying energy 'E' will be radiated , signifying the idea that mass is a sort of condensed form of energy . In this equation 'c' is the light speed in vacuum , though light speed varies with the medium apparently , the photons that make up the light always move at this constant 'c'.

BJ

16. Aug 26, 2005

### HallsofIvy

Oh, dear! I completely missed the "missing" 000!!

17. Aug 27, 2005

### xFlankerx

Sorry, its just a habit. I'll try to keep it to myself from now on. And I was asking the question in anticipation of someone else asking it, so I answered it as I thought fit in the next sentence.

Sarcasm or not? I can't tell.

18. Aug 27, 2005

### Pengwuino

How can people think that 300,000km/s is different then 300,000,000 m/s?

19. Aug 28, 2005

### h_k331

To be exact, the speed of light in a vacuum is actually 299,792.458 km/s.

hk

20. Aug 28, 2005

### pmb_phy

If the object in question is a particle then the E in the relation $E = mc^2$ is the inertial energy of the particle. c is the speed of like in a vacuum and has the value c = 299,792,456.2 m/s. m is the mass of the particle (and yelling will ensue if I don't point out that I'm speaking of relativistic mass). If the object is not a particle but a closed system of free particles or it is an object of finite size which is isolated in space then the same thing applies.

Pete