Fundamental Forces in Nature, Types, Effects, Laws of Motion

Fundamental forces of nature, the strong force, weak force, electromagnetic force, and gravitational force operate in the universe. These forces govern every interaction, from the tiniest subatomic particles to the largest cosmic structures. Each force differs in strength, range, and function, yet together they shape the fabric of matter, motion, and energy in the universe. 

While the strong and weak nuclear forces dominate at the atomic level, electromagnetic forces control most physical and chemical interactions, and gravity binds celestial bodies across vast distances. Understanding these fundamental forces in nature provides the foundation for modern physics, explaining everything from the stability of atoms to the motion of planets and the evolution of the cosmos itself.

Four Fundamental Forces in Nature

The four fundamental forces in nature, the Strong Force, Weak Force, Electromagnetic Force, and the Force of Gravity, control everything in the universe. They work over different ranges and have different strengths. All three fundamental forces except gravity are carried by gauge bosons, the force-carrying fundamental particles.

Strong Force

The strong force or strong interaction holds together the protons and neutrons in the nucleus; thus, it is an attractive force like gravity. It overcomes the repulsive forces between protons (due to the same charge), makes the atom stable and forms the essence of the elements.

• Mode of action: It holds the oppositely charged quarks that make up neutrons and protons together.
  • Within its range, gluon bosons (a fundamental particle) transmit the strong force between quarks and keep them "glued" together. 
  • A minute fraction of the strong force, called the residual strong force, acts between protons and neutrons. The residual strong force overcomes the repulsion between protons, so the particles stay bound in an atom's nucleus.

• Strength and limit: It is the strongest of all the forces, but is effective only over a very short range, at the level of subatomic particles.
  • It is about 100 times stronger than the electromagnetic force and 6✕1039 times stronger than gravity.
  • Contrary to the other fundamental forces, it is peculiar in that it becomes weaker as subatomic particles get closer to one another; the strongest interaction occurs when the particles are separated from one another the most. 
  • Its influence quickly diminishes for anything bigger than the nucleus of a medium-sized atom.

Weak Force

The weak force is responsible for how subatomic particles interact with one another and for transforming one type of subatomic particle into another.

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• Mode of action: W and Z bosons are the carriers of the Weak force. These bosons are exchanged between subatomic particles like protons, neutrons, and electrons when they are within 10-18 meters of one another. The result is the transformation into new subatomic particles.
  • In an atom, if a neutrino comes too close to a neutron, the neutron can become a proton while the neutrino itself transforms into an electron. Thus, it would turn that element into a different type. A down quark in a neutron is converted into an up quark in this process.
  • Examples are the phenomena occurring in the Sun and radioactive decay.
• Strength and limit: The Weak force is about a million times weaker than the Strong force, though it is still significantly stronger than Gravity.
  • It operates on the smallest distance scales, even smaller than that of the Strong force.

Electromagnetic Force

Electromagnetism includes both electricity and magnetism, unified by James Clerk Maxwell in 1865. They are linked - a moving electric field produces a magnetic field, and vice versa. Also called the Lorentz force (F = qE + qv × B), it includes the Electrostatic force (due to charge at rest) and the Magnetic effect of current (due to charge in motion). The stationary charge creates an electric field, whereas when in motion, it creates a magnetic field. 

• Mode of action: Electromagnetic forces are transmitted between charged particles through the exchange of bosons called photons (also the particle components of light waves).
  • These force-carrying photons are, however, a different manifestation of the photon particles.
• Examples of Electromagnetic force: 
  • It is the cause of some of the most frequently observed phenomena, including Friction between rough surfaces, Tension in strings, Elasticity in springs, Normal force (the apparent weight), and the Intermolecular force that holds the matter particles together.
  • Even our television sets are powered by this force - carried by light, it keeps electrons in orbit around atomic nuclei and allows chemical compounds to form.
• Strength and limit: Electromagnetism has an infinite range, and its force diminishes with the square of the distance between objects. It is stronger than gravity and the weak force,  but weaker than the strong nuclear force.

Gravitational Force

Gravity, the most familiar type of force, is the force of attraction between two masses or energy. It is the only force that does not fit into the Standard Model of Particle Physics. Thus, it is the only force that does not have a force carrier particle (although it has been hypothesised that a graviton might be that particle).

• • Gravity as per Newton: According to Newton, gravity is universal and between two objects having mass.
    • Its strength increases with the increase in mass but decreases with the increase in the distance between two objects.

• Gravity and the General Theory of Relativity: The general theory of relativity, developed by Albert Einstein, describes gravity as bending and curving (warping and ripples) in the fabric of space-time.

• • The presence of mass causes a warp and curve in space-time, which attracts objects together.
  • It is strongest where the spacetime is most curved, whereas it vanishes where the spacetime is flat.
• Effect of gravity on light: Gravity does not merely pull mass, but it also affects light.
  • Black holes have so much gravity that they absorb even light. 
  • Gravitational lensing is a phenomenon in which a large body, such as a galaxy cluster, causes the light to be curved (change in path), as if by a lens.
• Examples:
  • The effects of gravity are the most macro examples that we see in our daily lives, from experiencing weight to even observing geographical and geological phenomena.
  • Weight is the gravitational force exerted by the Earth on any object. Mathematically, it is equal to ‘mg’, where m is the mass of the object and g is the acceleration due to gravity, subject to the position of the object within the Earth’s gravitational field. 
• Strength and limit: Gravity is the weakest force, but strong enough to hold the stars (and our solar system), galaxies, and even the universe together. 
  • Like electromagnetic force, it has an infinite range, and its force diminishes with the square of the distance between objects.
  • In comparison to the other fundamental forces, gravity has almost no influence at the molecular and atomic level.

Fundamental Forces in Nature Effects 

When a force is exerted on an object, the position, velocity, etc. of the object is affected. The classical relationship between an object and the forces acting upon it is described by Newton's laws of motion. 

Fundamental Forces in Nature and Laws of Motion

• First Law of Motion: If the net external force on the object is zero (balanced), its acceleration would also be zero. 
  • That is, there will be no change in the object's state - it will continue to be either at rest or move with a constant velocity.
• Second Law of Motion: If the net external force is not zero, then there will be an acceleration of the object in the direction of the Net Force. 
  • The acceleration a will be equal to net Force/mass.
• Third Law of Motion: It states that every action (force) has an equal and opposite reaction. 
  • In other words, if object A exerts a force on object B, then B would also exert the same force, equal in magnitude but opposite in direction.
• Pseudo Force: Only an observer in an inertial frame of reference (one that is either at rest or moving at a constant speed) can accurately apply Newton's laws of motion. 
  • If not, the observer (of the non-inertial frame of reference) would need to apply an additional force (referred to as a pseudo force) to the object in the direction opposite to the observer’s own acceleration to ensure that the laws of motion are accurate.
  • The pseudo force is therefore not a real force. The observer with the non-inertial frame of reference is the only one who uses it.
  • Centrifugal force, Coriolis force, etc., are examples of pseudo-force.

Fundamental Forces in Nature and Work, Power & Energy

When the force is exerted on an object and if there is a change in the position of the object, we say that the work has been done on the object. They can also convert the energy of one form to another. 

• • Work: Work is calculated as the force multiplied by the displacement of the object in the direction of the force. The Newton meter (Nm) or joule (J) is the SI unit for work.
  • Power: Power is the rate at which an amount of work is completed per unit of time. The SI unit of Power is the Watt (W).

• Energy: Energy is the capacity to do work. It is the currency that must be spent to do any work. In other words, a body's energy equals the total amount of work it is capable of. 

• Unit: Energy is measured in the same unit as work, the joule (J). 

• Examples: Kinetic energy, Potential energy, Heat energy, Light energy, etc.

• Conservation of Energy: Energy cannot be created or destroyed but can only be transformed from one form into another. 

• Waves: Energy can be translocated from one point to another via waves (mechanical as well as electromagnetic waves).

Fundamental Forces in Nature PYQs 

Question 1. The known forces of nature can be divided into four classes, viz., gravity, electromagnetism, weak nuclear force, and strong nuclear force. With reference to them, which one of the following statements is not correct? (UPSC Prelims 2013)

1. Gravity is the strongest of the four
2. Electromagnetism acts only on particles with an electric charge
3. Weak nuclear force causes radioactivity
4. Strong nuclear force holds protons and neutrons inside the nucleus of an atom

Ans: (a)