Fundamental Forces

What is a Force?

A force is defined as an agent i.e. a push or a pull which keep a system in working condition. The concept of force was first developed by Sir Isac Newton. Hence, it is also called as a Newtonian force.

Therefore, a force is defined as an agent, which keeps a system in working condition.

Effect of a force

A force acting on a body can produce three types of changes –

1. It can produce acceleration or retardation in the speed of moving body, i.e. force can change the speed.
2. Force can change the direction of a moving object with or without change in its speed.
3. Force can produce a deformation and change in the shape of a rigid body.

What are called Fundamental Forces?

Forces generated due to inherent and fundamental interactions between the material particles of a body are called fundamental forces.

Examples of fundamental forces are –

1. Intra-molecular or intra-atomic forces between the molecules and atoms of different materials due to which nuclear or chemical reactions occur.
2. Inter-molecular or inter-atomic forces of attraction between the molecules and atoms of same material.
3. Inter-particle forces between the fundamental particles ( like electrons, protons, nucleus etc. ) of molecules or atoms of same material.
4. Gravitational force of attraction between all bodies in universe.
5. Electrostatic force of attraction or repulsion between two charged particles.
6. Magnetic force of attraction between two magnetic poles.

Non-fundamental forces

Forces generated due to all other reasons except fundamental interactions between the material particles are called non-fundamental forces.

Examples of non-fundamental forces are –

All other type of forces are non-fundamental forces, such as –

1. Surface tension.
2. Viscous force.
3. Friction force.
4. Buoyant force.
5. Elastic force.
6. Spring force etc.

Types of Fundamental Forces

Different types of fundamental forces are –

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

1. Strong Nuclear Force

A strong force of attraction exist in between the protons and neutrons present in the nucleus of an atom. This is called Strong Nuclear Force. It is represented by ( F_S ) .

It is the strongest force among all type of interactions found in nature.

2. Weak Nuclear Force

The force acting between elementary particles involved in a nuclear processes, is called Weak Nuclear Force. It is represented by ( F_W )

• ( \beta ) decay of a nucleus is a kind of weak nuclear force.

3. Gravitational Force

The force generated due to the inherent and fundamental interactions between the particles of two or more different bodies is called Gravitational force. It is represented by ( F_G )

• This is the force of mutual attraction between two bodies due to their masses.
• In universe everybody attracts to another body. Therefore, it is also called a universal force.

According to Newton’s laws of gravitation, we have –

F_G = G \left ( \frac { m_1 \times m_2 }{ r^2 } \right )

Here, ( m_1 ) and ( m_2 ) are masses of two bodies separated by a distance ( r ) and ( G ) is the universal gravitational constant.

4.Electromagnetic Force

The force generated due to the inherent and fundamental interactions between the particles of same body is called Electromagnetic force. It is represented by ( F_E )

Electromagnetic force is a combination of two fundamental forces which are inseparable in nature. These are –

1. Electrostatic force ( F_e ) .
2. Magnetic force ( F_m ) .

Thus, \quad F_E = ( F_e + F_m )

(a) Electrostatic force

Force of attraction or repulsion between two electrically charged bodies at rest is called electrostatic force. It is represented by ( F_e ) .

Magnitude of electrostatic force is obtained by Coulomb’s law of electrostatics. According to this –

F_e = \left ( \frac { 1 }{ 4 \pi \epsilon_0} \right ) \times \left ( \frac { q_1 \times q_2 }{ r^2 } \right )

Here, ( q_1 ) and ( q_2 ) are magnitudes of two charges which are kept at a distance ( r ) in a vacuum medium of permittivity ( \epsilon_0 ) .

(b) Magnetic force

Force of attraction or repulsion between two magnetic poles is called magnetic force. It is represented by ( F_m ) .

Magnitude of magnetic force is obtained by Coulomb’s law of magnetic forces. According to this –

F_m = \left ( \frac { 1 }{ 4 \pi \epsilon_0} \right ) \times \left ( \frac { Q_1 \times Q_2 }{ r^2 } \right )

Here, ( Q_1 ) and ( Q_2 ) are magnitudes of two magnetic poles which are kept at a distance ( r ) in a vacuum medium of permittivity ( \epsilon_0 ) .

Nature of Electromagnetic Force

Electromagnetic force has following characteristics –

1. Electrostatic force and magnetic force are inseparable in nature. Both forces generate together on the same body. They can’t be separated from each other.
2. In fact electric charge produces electrostatic force and magnetic field produces magnetic force. Both forces generate simultaneously in one body.
3. Thus we can say that, if a body has electrostatic force due to electric charges, by nature it must have magnetic forces due to naturally created magnetic field.
4. Hence, electrostatic force and magnetic force both are inter-dependent on each other and are inseparable. These two forces are the two facets of electromagnetic force.

Comparison of strength of Fundamental Forces

By comparing the strength of four types of fundamental forces in nature, we get –

F_G < F_W < F_E < F_S

Ratio of their absolute values is given by –

F_G : F_W : F_E : F_S = 1 : 10^{25} : 10^{35} : 10^{38}

Therefore, among all fundamental forces, strong nuclear force is the strongest force and gravitational force is weakest force.