12.2 Fundamental Forces of Nature

12.2 Fundamental Forces of Nature

To understand the structure of the nucleus, it is important to know the nature of the forces that bind the nucleon together. But before that, we should know the basic forces in nature. Despite the apparent complexity within the universe, all interactions in the universe are governed by the four basic forces, known as fundamental forces. These forces control how objects move, interact and behave at different scales from nucleons in the atom to massive galaxies. The four fundamental forces are gravity, electromagnetism, weak nuclear force, and strong nuclear force.

Gravitational force or gravity is one of the four fundamental forces of nature. It is the weakest of the four but it is a long-range force. It is an attractive force and arises due to the gravitational interaction between the bodies. The gravitational force between two bodies is proportional to the product of their masses and inversely proportional to the square of the distance between them. When considered for massive objects, such as the Sun, or giant planets, gravitational force is considered to be significant as the masses of these objects are large. However, on an atomic level, this force is considered to be negligibly weak.

The electromagnetic force is responsible for electric field and magnetic field interactions. Like the gravitational force, the electromagnetic force follows an inverse square law but is much stronger than gravity. It governs a vast range of phenomena, from atomic structure, chemical bonding, electricity, magnetism, and light propagation. James Clerk Maxwell (1861) formulated a set of four fundamental equations named as "Maxwell's equations" that unified electricity and magnetism into electromagnetism. These equations describe how electric and magnetic fields interact and how electromagnetic waves propagate. These equations showed that electric and magnetic fields are not separate forces but are two aspects of a single electromagnetic force.

Out of the four fundamental forces, nuclear forces are the strongest attractive forces. Electromagnetism holds the matter together, but there was no explanation on how the nucleus is held together in the atom. If we only consider the forces of electromagnetism and gravity, the nucleus should fly off in different directions. The stability of the nucleus implies that another force should exist within the nucleus which is stronger than the gravitational force and electromagnetic force. This is where nuclear forces come into play. Strong nuclear forces are responsible for holding the nuclei of atoms together. They only exist inside the nucleus. So, we call them as short-range forces. The strong nuclear force acts as an attractive force between all nucleons. Thus, protons attract each other via the strong nuclear force at the same time they repel each other via the electric force. A neutron, being electrically neutral, can attract other neutrons or protons via the strong nuclear force. Weak nuclear forces are responsible for the radioactive decay, particularly the beta decay and interactions involving neutrino. Unlike the other fundamental forces, the weak force can change the identity of particles, making it essential for processes like nuclear fusion in stars and the decay of unstable atomic nuclei. The relative strength and range of the above four forces are given in Table 12.1.

Table 12.1: Relative Strength and Range of Fundamental Forces