Describe the nuclear force and its characteristics.

(N/A) The nucleus is the central part of the atom. It contains positively charged protons and electrically neutral neutrons.
The Coulomb repulsive force between two protons acts at all distances,both small and large. However,nucleons are held tightly together in the tiny region of the nucleus.
This indicates that another attractive force must exist between nucleons in the nucleus,which is strong enough to overcome the Coulomb repulsive force and hold them together.
The force acting between two protons,two neutrons,or a proton and a neutron in a nucleus is called the nuclear (or strong) force.
The constancy of binding energy per nucleon can be understood in terms of the short-range nature of this force.
Following are the key features of the nuclear force determined from experiments conducted between $1930$ and $1950$:
$(i)$ The nuclear force is much stronger than the Coulomb force acting between charges or the gravitational force between masses. This is why it binds protons and neutrons together in the nucleus.
$(ii)$ The nuclear force between two nucleons falls rapidly to zero as their distance increases beyond a few femtometres $(fm)$. This leads to the saturation of forces in medium or large-sized nuclei,which is the reason for the constancy of the binding energy per nucleon.
$(iii)$ The force is attractive for distances greater than $r_0$ and strongly repulsive for distances less than $r_0$,where $r_0$ is approximately $0.8 \ fm$.