# Mass Defect Explained

• benzun_1999

#### benzun_1999

My friend was telling about something called mass defect. what is it correctly?

-benzun
All For God

Basically people measured the masses of individual protons and neutrons, and then measured the masses of the nuclei of the elements of the periodic table. They found that the masses of the nuclei were less than they expected, i.e. a carbon-12 nucleus, with 6 protons and 6 neutrons, did not measure as much as 6 individual protons + 6 individual neutrons.

This is due to the fact that the protons and neutrons are bound together in the nucleus by the strong and weak nuclear forces. To split a nucleus up into its individual components, energy must be input into the nucleus. This energy is called the 'binding energy' of that particular nucleus, and since E = mc^2 the binding energy corresponds to a mass. The binding energy is equal to the difference in mass between the nucleus and the composite protons and neutrons.

Jess

so does this break the law of conservation of mass?
My friend was telling that einstine's equation E=mc^2 has something to do with it. he also told that when we pass light through some solution(i am not sure of the name ) electrons get formed is this true?

I hope someone will help me.

-Benzun
all for God.

Originally posted by benzun_1999
so does this break the law of conservation of mass?

as far as I know this law applies for chemical reactions.
http://science10.dev.kcdc.ca/chemunit/lawmass.html [Broken]

as Jess said when you gather toghether protons and neutrons in a nucleus, you need some energy to keep them together (protons are positively charged and they tend to repel each other). This energy is used by the strong nuclear force. So let's say you have 6p and 6n and a C12 nucleus. if you measure the mass for all this you'll find that:

mass of C12 + md = mass of (6p and 6n)

where md (mass defect) = e/c2, that means exactly the energy required to keep the neutrons and protons together.

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Indivisible particles

There is something about the mass defect that I cannot understand, if the consituant particles of the nucleus are indivisible how can they give up just some of their energy to bind, surely quarks have a constant mass (if at rest) and can therefore only be converted entirely to energy, which of course is not observed

Originally posted by AlanPartr
There is something about the mass defect that I cannot understand, if the consituant particles of the nucleus are indivisible how can they give up just some of their energy to bind, surely quarks have a constant mass (if at rest) and can therefore only be converted entirely to energy, which of course is not observed

No particles, including quarks don't have constant mass. Particles have a rest mass when solitary (not quarks as they never are)and moving v slow, and a lower mass when bound up in a nucleus. Some of the mass is converted into binding energy. If they speed up they gain mass.
Being indivisible does not mean the same as having a fixed, constant mass.