# How much of a hydrogen atom's mass is due to the mass of fundamental particles?

1. Oct 1, 2011

### Runner 1

If one were to subtract the kinetic energies of all fundamental particles within hydrogen, as well as all of the potential energy of all bound states between these particles, how much mass (as a percentage of the total) would remain? Ignore the kinetic energy due to the hydrogen's speed.

And while I'm at it, isn't it weird that fundamental particles can be converted into the motion of another particle? For instance, an electron can be annihilated with a positron, producing photons which can in turn be absorbed by the electrons in another atom, promoting them to a higher state. In effect, one electron has been turned into the motion of a different electron!

2. Oct 2, 2011

### Staff: Mentor

A 1H atom (938.738 MeV/c²) is composed of 1 electron (0.510999 MeV/c²) 2 up quarks (2.2 MeV/c²) and 1 down quark (5.0 MeV/c²). So the mass of all of the fundamental particles is 9.9 MeV/c² (1% of total) and the remaining 928.9 MeV/c² (99% of total) is contained in the fields etc (predominantly the strong force).

3. Oct 2, 2011

### mrspeedybob

Doesn't it kind of depend on where you draw the line between field and particle? For example if you considered gluons to be component particles then the total would be higher then 1%.

4. Oct 2, 2011

### Staff: Mentor

Yes, I was drawing the line between fermions and bosons. Since the OP specifically mentioned the PE of the bound states I figured that was the line he wanted drawn.

5. Oct 2, 2011

### Runner 1

Okay, thanks for the reply! That's very interesting.

6. Oct 2, 2011

### Staff: Mentor

It's simply the conversion of energy between different forms: rest-energy $E_0 = m_0 c^2$ (where $m_0$ is rest-mass) on the one hand and kinetic energy on the other.

7. Oct 2, 2011

### Runner 1

Yeah, I still think it's weird haha.

8. Oct 2, 2011

### tasp77

Interesting.

So when the sun shines on me, I am experiencing 100% energy, but when I hoist a glass of water, I am not hoisting 100% mass.

Wonder what 100% mass mass (if you catch my drift) would be like?

9. Oct 2, 2011

### Runner 1

Haha not really. Energy is basically a numerical value that can be calculated from a system that is conserved through time despite any transformations of the system.

If you shine light into a box with perfect mirrors and weigh the box, it will weigh more than if you weighed just the box alone.