Fundamental Forces In Nature

We all experience several forces in day-to-day lives. For example, when a moving object hits us, we experience the impact of forces on us. We need a force to push, carry or throw objects, deform or break them. Sir Isaac Newton told the correct notion of force in his famous laws of motion. He also gave the correct explanation for the force of gravitational attraction between the two bodies. In addition to the gravitational force in the macroscopic world, we experience several kinds of forces:

• Muscular force
• Contact forces between bodies
• Friction force
• Forces exerted by springs and strings
• Force of buoyancy
• Viscous force when solids are in contact with fluids
• Force due to pressure of a fluid
• Force due to surface tension of a liquid, etc.

All these forces actually arise from the four fundamental forces in nature. So, let’s understand one by one in simple words.

Types of Fundamental Forces in Nature

There were five fundamental forces in nature till 1870. They are: gravitational, electric, electric, magnetic, strong nuclear and weak nuclear forces. Between 1860 and 1873, James Maxwell demonstrated that electric and magnetic forces are interdependent.

After this, there are four basic or fundamental forces in nature that govern the various phenomena of macroscopic and microscopic world. These forces are as:

• Gravitational force
• Electromagnetic force
• Strong nuclear force
• Weak nuclear force

Let’s understand each force in nature one by one.

Gravitational Force

The force of mutual attraction between any two objects due to their masses in the universe is called gravitational force. Sir Isaac Newton discovered this force in 1665 after watching an apple fall and asking why the apple fell straight down, rather than sideways or even upward.

Every object experiences this force due to the presence of every other object in this universe. Therefore, it is also called universal force. It means that every object attracts each other in this universe. For example, all the material bodies or objects on the earth experience the force of gravity due to the earth. All the objects on the earth exist due to gravitational force between them and the earth.

The moon and artificial satellites move around the earth due to the gravitational force between them and the earth. The gravitational force governs the revolution of earth and other planets around the sun between the sun and planets. It also governs the motion of bodies falling to the earth. The gravitational force plays a significant role in the large-scale phenomena of the universe, such as formation and evolution of stars, galaxies and galactic clusters.

Since Isaac Newton discovers the gravitational force, it is known as Newton’s law of gravitation. This law state that the mutual force of attraction between any two objects in the universe is directly proportional to the product of the mass and inversely proportional to the square of distance between them. Mathematically, we can express it as:

Gravitational Force F = G*m₁*m₂ / r²

Here, m₁ and m₂ are two point masses separated by a distance r and G is a universal gravitational constant which has the value 6.67 * 10^-11 N-m²/kg².

Characteristics of Gravitational Force

There are the following important characteristics that you should keep in mind. They are as:

• Gravitational force is a universally attractive force in nature. That is, it is always attractive.
• The force between two objects is equal in magnitude and opposite in direction.
• Gravitational force is the weakest force in nature.
• Gravitational force between two objects is independent of the pressure, and intervening medium.
• It is a long range force, meaning that it is effective even if the distance between separation is large.
• Gravitational force is a central force, meaning that it acts along the line, joining the centres of two interacting objects.
• Gravitational force obeys inverse square law, meaning that it varies inversely as the square of the distance between two objects. In simple words, gravitational force between the two bodies decreases with distance.
• This force is conservative in nature, meaning that work done by this force is independent of the path followed by the body. It only depends on the initial and final position of the body.

Electromagnetic Force

The force between charged particles is called electromagnetic force. The electrostatic force and magnetic force constitute it.

Electrostatic Force

The force between two static electric charges at rest is called electrostatic force. This force is attractive between two opposite charges and repulsive between like charges. In simple words, like charges repel and unlike charges attract with each other. When charges are at rest, the force is given by Coulomb’s law.

According to Coulomb’s law of electrostatics, the force of attraction or repulsion between two point changes is directly proportional to the product of charges and inversely proportional to the square of the distance between them. Mathematically, we can express it as:

$\begin{array}{l}F=\frac{1}{4\pi {\in }_0}\frac{q_1{q}_2}{r^2}\end{array}$

In the above mathematical formula, q₁ and q₂ are the two point charges separated by a distance r. ε₀ is a constant called the permittivity of free space.

Magnetic Force

The force acting between two magnetic poles is called magnetic force. Like poles repel and unlike poles attract. The magnetic force occurs due to the motion of charges. When a moving electric charge enters a magnetic region, it produces force. The moving charge produces magnetic effects and a magnetic field gives rise to a force on a moving charge. Due to charge, electric and magnetic effects are inseparable. Hence, the force between charges is called electromagnetic force.

Characteristics of Electromagnetic Force

There are the following characteristics of electromagnetic force that you should keep in mind. They are as:

• Electromagnetic force may be either attractive or repulsive in nature. Coulomb’s law controls this force.
• Like gravitational force, electromagnetic force also obeys inverse square law.
• Electromagnetic force is also a long range force and acts over large distance. It does not require any intervening medium.
• Electromagnetic force is a very strong force as compared to gravitational force. It is 10³⁶ times stronger than gravitational force.
• This is a central force as well as conservative force.
• Electromagnetic force dominates all phenomena at atomic and molecular scales. It governs the structure of atoms and molecules, dynamics of chemical changes, and the mechanical, thermal and other properties of materials.
• The macroscopic forces like tension, friction, normal force, spring force, etc. are the examples of electromagnetic force.

Strong Nuclear Force

The force which binds protons and neutrons together inside a tiny nucleus is called strong nuclear force. Without attractive force, a nucleus will be unstable due to the electric repulsion between its protons. This attractive force cannot be gravitational because the force of gravity is negligible compared to the electric force.

Therefore, there is a new attractive force acting between a proton and a proton, a proton and a neutron, between two neutrons inside the tiny nucleus. This force is called nuclear force, and it is the strongest force in nature.

Characteristics of Strong Nuclear Force

There are several characteristics of strong nuclear force that you should keep in mind. They are as:

• The nuclear force is the strongest of all fundamental forces in nature, about 100 times the electromagnetic force in strength.
• It is an attractive force in nature and acts between proton-neutron, proton-proton, and neutron-proton.
• It is basically a short-range force that exists only inside the nucleus diameter 10^-15 meter.
• The strong nuclear force does not depend on the nature of charge, meaning that the force between neutron-neutron, and proton-proton is the identical.
• The strong nuclear force is responsible for the stability of nuclei. However, the electron inside the atom does not experience this force.
• This force is not central force as well as does not obey inverse square law.
• In 1935, Yukawa’s theory explained the existence of strong nuclear forces between nucleons.
• The strong nuclear force is a non-conservative force.

Weak Nuclear Force

The force between the elementary particles emitted during radioactive decay of a radioactive substance is called a weak nuclear force. This force exists only in certain nuclear processes, such as the β-decay of a nucleus. In the β-decay process, the nucleus releases an electron and an uncharged particle called neutrino.

This was the first particle predicted by Wolfgang Paul in 1931. Compared to the strong nuclear and electromagnetic forces, the weak nuclear force is much weaker, but it is stronger than the gravitational force. The range of weak nuclear force is extremely small, of the order of 10–16 m.

Comparison between Four Fundamental Forces in Nature

Unification of Different Forces in Nature

Unification of forces is an idea in which physicists had attempted to weave all of nature’s fundamental forces into a single comprehensive force. They had made a number of attempts towards the unification of different theories and domains of physics. For example, Newton unified terrestrial and celestial mechanics under a common law of gravitation in 1687. He showed that the same law can be applied to both domains.

In 1820 and 1830, the experimental discoveries of Hans Christian Oersted and Michael Faraday demonstrated that electric and magnetic phenomena are, in general, inseparable and gave rise to a united domain electromagnetism. In 1873, James Maxwell unified electromagnetism and optics with the discovery that light is an electromagnetic wave. Einstein attempted to unify gravity and electromagnetism but could not succeed in this attempt.

In 1979, Sheldon Glashow, Abdus Salam, and Steven Weinberg provided the idea of electro weak force, that is the combination of weak nuclear force and electromagnetic force. In 1984, Carlo Rubbia and Simon Vander Meer had experimentally verified the theory of electro-weak force.

The below table summarizes some of the achievement towards the unification of fundamental forces in nature.