A nucleus contains protons & neutrons inside its small size. For such a small distancethe coulomb’s repulsive force between two protons must be extremely large so that they should fly off away from nucleus, but it not so happened because of the strong force existing between the nucleons.
Strong force of attraction existing between nucleons are named as nuclear force.
Properties of Nuclear force
1. It is a short range force.
A rough plot of potential energy between two nucleons as a function of distance is shown in a graph.
The nuclear force between two nucleons falls rapidly to zero as their distance (r) is more than a few femtometre.
The potential energy is minimum at r0 of about 0.8 fm. It means the force is attractive for distances larger than 0.8 fm and repulsive if they are separated by distances less than 0.8 fm.
2. They are charge independent i.e inside the nucleus, the attractive force between two nucleons are of three types- proton – proton, neutron – neutron and proton – neutron of having approximately same magnitude.
3. They are non-central forces.
4. They are saturated force. i.e A nucleon inside the nucleus does not experience nuclear force due to all other nucleons.
Nuclear forces are basically strong attractive forces, but contain a small component of repulsive forces – the nuclear force becomes attractive at r0 = 0.8 fm (approx.) and changes into a repulsive force when r0 < 0.8 fm. This repulsive part saves nucleus from collapsing.