Ask A Scientist Physics Archive

name         Matt J.
status       student
age          15

Question -   How do protons within the nucleus stay so tightly 
packed if they have the same charge?
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Matt,

The nucleus of atoms are held together by one of the four fundamental
forces called The Strong Force.  It is a very strong force but it acts
over a very short range.  It is an exchange force with exchange
particles called pions and other heavy particles.

Bob Hartwell
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Dear Matt,

The protons (and neutrons) in a nucleus are held together by the "strong
force".  This force is about 100 times stronger than the electromagnetic
force which produces the repulsive force between objects with the same sign
of charge.  The range of the strong force, however, is very short -- about
1.0E-13m = 0.0000000000001 meters, which explains why all nuclei are this
size or somewhat larger.  The electromagnetic force has an infinite range,
like gravity, though it falls off in strength rapidly as the charged
particles get further apart.

This explains why nuclei became less stable and some decay as the number of
protons in the nucleus increases,  Uranium, which has 92 protons and 146
neutrons in its nucleus is the most massive nucleus which is stable.  The
fact that it is barely stable explains why it gives up energy when it splits
into smaller and more stable nuclei and so can be used to generate
electrical power and to make nuclear bombs.

Best, Dick Plano...
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