Why gravitational force is present between nucleus?

Gravitational force should exist between ANY pair of particles; but for individual particles, this force is extremely weak. It is the cumulative effect of lots of particles attracting each other that causes an enormous force between you and Earth, Sun and Earth, etc.

Gravitational force should exist between ANY pair of particles; but for individual particles, this force is extremely weak. It is the cumulative effect of lots of particles attracting each other that causes an enormous force between you and Earth, Sun and Earth, etc.

Gravitational force should exist between ANY pair of particles; but for individual particles, this force is extremely weak. It is the cumulative effect of lots of particles attracting each other that causes an enormous force between you and Earth, Sun and Earth, etc.

Gravitational force should exist between ANY pair of particles; but for individual particles, this force is extremely weak. It is the cumulative effect of lots of particles attracting each other that causes an enormous force between you and Earth, Sun and Earth, etc.

Gravitational force should exist between ANY pair of particles; but for individual particles, this force is extremely weak. It is the cumulative effect of lots of particles attracting each other that causes an enormous force between you and Earth, Sun and Earth, etc.