1. Nuclear Forces

2. There are four fundamental forces in nature, these are:
1- The nuclear force is the strongest of the four, but it is limited to submicroscopic systems (nuclei)
2- The electromagnetic force, whose strength is on the order of that of the nuclear force, is the dominant force in microscopic systems, such as atoms and molecules.
3- The weaK-interaction force, whose strength is only that of the nuclear force, plays a role in interactions involving radioactive particles.
4- The gravitational force is the weakest of all four forces, but it is the dominant force in macroscopic systems, such as the solar system. -2 -4

3. Since nucleus contains protons that are positively charged particles, the forces acting between them should be the forces of repulsion. If there were no other forces acting between these particles the nucleus can not retain a stable structure because of the repelling forces. To have stability of the nucleus we have to assume that there must be strong attractive forces which hold the nucleons together in the nucleus. These attractive forces dominate the forces of repulsion. It is therefore necessary to postulate an entirely new type of forces known as "nuclear forces".

4. Properties of Nuclear Forces
1. Nuclear forces are attractive forces between proton and neutron (p-n), proton and proton (p-p) and neutron and neutron (n-n).
2. Nuclear forces are charge independent. It was found that nuclear force between two protons is the same as that between a proton and a neutron or between two neutrons.
3. Nuclear forces are the strongest in nature.
4. Nuclear forces are short range forces. Short range means, they are applicable with in the distances of the order of 10 m (1 fm). At greater distances these forces are negligible.
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5. 5. Nuclear forces are spin dependent
5. Nuclear forces are spin dependent. Forces between nucleons are strong when spins are parallel and weak when spins are anti-parallel.
6. Nuclear forces are non-central forces which implies that they do not act along the line joining the two nucleons.
7. Nuclear forces are saturated forces. It means the each nucleon attracts only those nucleons which are its immediate neighbours. It does not interact with all the nucleons.
8. Nuclear forces are exchange forces. The nuclear forces between the two nucleons is the result of the exchange of n mesons (n°,n+,n- ) between them.