Physical World

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There are four fundamental forces which govern both macroscopic and microscopic phenomena. There are

1. Gravitational force
2. Strong Nuclear force
3. Electromagnetic force
4. Weak nuclear force

The relative strengths of these forces are

Fg :Fw:Fe:Fs=1:10²⁵:10³⁶:10³⁸

All those quantities which can be measured directly or indirectly and in terms of which the laws of physics can be expressed are called physical quantities.

The strong nuclear force binds protons and neutrons in a nucleus. It is evident that without some attractive force, a nucleus will be unstable due to the electric repulsion between its protons.

The strong nuclear force is the strongest of all fundamental forces, about 100 times the electromagnetic force in strength.

It is charge-independent and acts equally between a proton and a proton, a neutron and a neutron, and a proton and a neutron.

The electromagnetic force is the force between charged particles.

This force is known as a non-contact force because these forces come into play even when the bodies are not in contact with each other.

The gravitational force is the force of mutual attraction between any two objects by virtue of their masses. It is a universal force. Every object experiences this force due to every other object in the universe.

It plays a key role in the large-scale phenomena of the universe, such as formation and evolution of stars, galaxies and galactic clusters.

The physical quantities that remain unchanged in a process are called conserved quantities.

The general conservation laws in nature include the laws of conservation of energy, mass, linear momentum, angular momentum, charge, parity, etc. Some conservation laws are true for one fundamental force but not for the other.

The weak nuclear force appears only in certain nuclear processes such as the β-decay of a nucleus. In β-decay, the nucleus emits an electron and an uncharged particle called neutrino. The weak nuclear force is not as weak
as the gravitational force, but much weaker than the strong nuclear and electromagnetic forces. The range of weak nuclear force is exceedingly small, of the order of 10^-16 m.