what does c-squared have to do with mass?

[ishmael]

Please indulge my naivete here.

Is Einstein's famous equation a precise statement of the relation of energy and matter?, or is it just a way of saying there is a whole lot of energy locked up in matter? I just don't understand why the speed of light is used as the multiplier here. And what is the unit of energy that is the result of this multiplication? ergs, joules, volts.....?

[Amr Morsi]

The main equation is E=sqrt((p*c)^2+(m*c^2)^2).

When the particle is at rest, p is zero, and then you get E=m*c^2. It is called the Rest Energy. And it is the total energy confined in mass m.

 

When m is in Kgs and c in m/s, the unit for E is Joule.

[Bob_for_short]

Is Einstein's famous equation a precise statement of the relation of energy and matter?, or is it just a way of saying there is a whole lot of energy locked up in matter? I just don't understand why the speed of light is used as the multiplier here. And what is the unit of energy that is the result of this multiplication? ergs, joules, volts.....?

 

What A. Einstein obtained was ∆E = ∆m c^2, i.e., change in energy leads to change in mass of a body. c-squared is here because it was derived for light emission/absorption that carry some energy-momentum expressed with help of c. The true meaning of the formula E = m c^2 was established after discovery of antiparticles. Then the total mass of a particle-antiparticle system can be transformed into the energy of photons and vice versa.

 

If you know, kinetic energy is also expressed as a product mv^2/2 so it has the same dimension - joules, ergs, or electron-volts, depending on the unit system chosen.

Edited April 3, 2010 by Bob_for_short

[michel123456]

Please indulge my naivete here

 

If you are naive, I am naive^2.

 

Is Einstein's famous equation a precise statement of the relation of energy and matter?, or is it just a way of saying there is a whole lot of energy locked up in matter?

It is the usual interpretation. I fight against this constantly, because the multiplier has units.

 

 

 

I just don't understand why the speed of light is used as the multiplier here.

It is not not. Csquared is the multiplier, with bizarre units of m^2/s^2.

 

 

And what is the unit of energy that is the result of this multiplication? ergs, joules, volts.....?

 

Joule = kg m^2 / s^2