# Kinetic energy compared to energy making up mass

1. Jul 24, 2014

### sambogrub

I knew this may not be possible, but I was wondering if you can compare kinetic energy with the energy that makes up mass? When I say that, I mean the mass of our atoms that is represented by a quantity of energy.

2. Jul 24, 2014

### mathman

Kinetic energy depends on the speed of the object, mass energy is intrinsic. At ordinary speeds, K.E. = mv2/2 while mass energy is mc2. Since v << c, the conclusion is obvious.

3. Jul 24, 2014

### sambogrub

But I had read that the equation E=mc^2 is very vague and cannot completely express energy in a mass. I mean in this question, is the energy we talk about in the above equation the same energy as what is expressed in a velocity equation? I know they are different concepts and different aspects are involved. But im trying to determine if when you insert energy into a system in the form of thrust, is that energy the same as the energy making up most of the mass of an atom.
Im trying to wrap my mind around gravity and its effects on the space time field. Im wondering if the amount of energy that is inside a mass is what affects the field.

4. Jul 25, 2014

### mathman

I don't understand most of your comment.
However E = mc2 refers to any process, such as nuclear fission or nuclear fusion where the total mass of the outgoing particles is less than the total mass of the incoming. The mass difference appears as energy, usually in the form of gamma rays. In addition when a particle (such as an electron) annihilates its antiparticle twin (such as a positron) all the mass is converted into energy.

Last edited: Jul 25, 2014