# Binding energy and mass

1. May 25, 2010

### Jerbearrrrrr

Very basic questions, since I don't know anything about anything.

What do we mean by a particle's mass, and how can we measure it? This is with regards to measuring mass defects after a nuclear reaction.
(We may as well just define mass as the number that comes out after doing a certain measurement I guess)

In SR, we end up with a relation E=mc² (+½mv²). What precisely can be inferred from that (in the presence of other assumptions, perhaps)? To me, this ends up helping us understand how a particular 4-norm is conserved in SR.

How do we get from here to the conclusion that splitting an atom releases energy?
(I suppose it's saying that, first set v=0, then if the same thing weighs different amounts after an interaction, and it can be guaranteed that only 'm' has changed, there will be a corresponding E somewhere out there?)

Say an atom A releases energy when fissioned. The mass of A's daughters will sum to less than A's mass, right?
Are we then interpreting the "missing mass" as the "mass" of the binding energy?
In the sense that the presence of binding energy affects a certain measurement, the outcome of which is said to be something's mass.

Thanks

2. May 26, 2010

### ansgar

one can measure the energy of the decay products in the detectors