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Universal Forces are those forces present throughout the universe. The fundamental forces that are counted as universal forces are- gravitational force, electromagnetic force, weak nuclear force, and strong nuclear force. From the movement of galaxies in outer space to the smallest interactions of atoms in a chemical reaction is all monitored by these basic forces.
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Key Takeaways- Universal force, gravitational force, electromagnetic force, weak nuclear force, strong nuclear force, unifying forces
Read More: Physical Significance of Electric Field
Four Fundamental Forces
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Universal forces control all other forces of physics.We experience gravitational force all the time. Out of the four basic forces, strong nuclear force is the strongest, and gravitational force is the weakest. All the other forces in nature are dependent on these four fundamental forces. The gravitational force has an effect over a large area while strong nuclear force affects smaller areas.
Four Fundamental Forces
The most common force which is strong enough to affect a reasonable distance is the electromagnetic force. The other two forces are confined within the nucleus of an atom and its interaction with neutrons, protons, and other particles. Scientists are finding ways to unify all the four fundamental forces.
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Gravitational Force
Gravitational force is the most common force which we can relate easily as it is a part of our common observations. It exists between any two bodies with mass. Astronomically, the gravitational force is the prominent force in controlling the motion of planets, the moon, and galaxies. When you stand on a weighing machine, the weight that you see is a combination of your mass and the effect of gravity on your body. It is the largest attractive force on earth but has a weak magnitude.
Gravitational force
It is a known fact that gravitational force is the weakest of all fundamental forces despite it being covered over a large area. A simple bar magnet can easily overcome the gravitational force and exert its magnetic force on an iron nail against the gravitational force which pulls it in the opposite direction. Whereas the entire mass of the earth is required to hold the iron nail to the ground. The nature of space and time is also controlled by gravitational force.
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Electromagnetic Force
As the name suggests, the electromagnetic force is a combination of electric and magnetic forces. When a magnet rotates inside a coiled conductor or moves across it regularly, it produces electricity in that conductor. This gives rise to an electromagnetic field and the force produced is the electromagnetic force. There is an interaction of particles in thus produced electric charge.
Electromagnetic Force
Electrostatic forces are produced through the interaction of static particles while magnetic and electrical forces are produced through the interaction of particles in motion. The electromagnetic force is stronger and has a higher magnitude than the gravitational force. It can act both as an attractive or repulsive force. Our body contains ionic bonds, hydrogen bonds that involve electromagnetic force in molecular connections. It exists between charged bodies.
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Weak Nuclear Force
The weaker nuclear force is weaker than the stronger nuclear force, but it is not weaker on an atomic scale. Beta-decay happens due to weak nuclear force, this decay is when a beta particle requires the weak nuclear force to drift away from the strong attractive force of the nucleus. The weak nuclear force is still stronger than the gravitational force.
Weak Nuclear Force
Strong Nuclear Force
An atom consists of a nucleus with protons and electrons revolving around it. These atoms need to have an attractive force from the nucleus to keep electrons, protons, and neutrons intact. The nucleus has protons that are positively charged, and keeping such repelling forces together requires a greater nuclear force.
Strong Nuclear Force
To keep the whole body intact, each atom should have this nuclear force that should be greater than the gravitational force. Instead of repelling the similar poles of protons, they are still binding together, which means the nuclear force is greater than the electromagnetic force. This force is an attractive force. This short-range nuclear force is so strong that it keeps the neutron-neutron, neutron-proton, and proton-proton connections bound together.
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Properties of Fundamental Forces
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| Force | Approximate Relative Strength* | Range in Meters | Carrier Particle** | Type of force (attractive or repulsive) |
|---|---|---|---|---|
| Gravitational | 10-41 | ∞ | Graviton (theorized and not confirmed) | Attractive only |
| Weak Nuclear | 10-16 | 10-18 | Boson | Attractive and repulsive |
| Electromagnetic | 10-3 | ∞ | Photon | Attractive and repulsive |
| Strong Nuclear | 1 | 2×10-15 | Gluons [Pi mesons / pions] | Attractive and repulsive |
| *Approximate relative strength is dependent on the strong force felt by the proton-proton pair | ||||
| **Carrier particles are those particles that are used for transmitting the force through the exchange of particles among the charges/ protons/ atoms /objects in the force field. | ||||
Unification of Fundamental Forces
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- It is believed that all of these four forces have a unified force underlying which is yet to be discovered.
- Attempts are made to unify all the four fundamental forces into one. Scientists are still working on finding common connections between the four forces to identify the underlying common force.
- They predict that such unification can only exists in extreme conditions. Suppose unification is achieved, the forces will still remain in their current state on the macroscopic scale.
Unification of Universal Forces
- The early universe had extreme conditions like high temperature and density which made electromagnetic force and weak nuclear force exist without any difference between them. At high energies, these forces can be unified to be called electroweak forces.
- The electromagnetic force itself is a combination of electrical and magnetic forces.
- Gravitational forces tend to change space and time according to the mass of the planet. We know that other forces are dependent on space and time and changes in them can bring about the anomaly. 'Quantum Gravity' is when gravity is unified with other forces. The special characteristics of gravitational force make it difficult to achieve quantum gravity.
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Things to Remember
- Gravity affects space and time interestingly. Massive bodies have higher mass thus they possess greater gravitational force. These forces tend to bend space and time around that object making time slower with increasing gravity.
- Similar poles repel and opposite poles attract.
- Distance and magnitude play an important role in understanding the strength of a force.
- Carrier particles are also studied as the force field that helps in transferring force.
- The Gluons which exist in the strong nuclear force field are known to have strong binding power.
- Undoubtedly, photons, the energy packets, exist in the electromagnetic force field between charged particles.
- The weak nuclear force causes decay and loss of mass thus the Boson has W- negative carrier, W+ the positive carrier, and Z0 zero charge carrier.
- The graviton particle for gravitational force is not yet discovered but it is theorized.
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Sample Questions
Ques. Why is gravity a non-contact force? (2 marks)
Ans. Gravity exerts a force on another object without actually coming in contact with it thus it is a non-contact force. A ball thrown up automatically returns to the ground, during this gravity was exerting force on the ball even when it was in mid-air that's why it came towards the force.
Ques. Assuming that the Earth's orbit is a circle of radius 1.5 ×108km. Calculate the mass of the sun. (4 marks)
Ans. The gravitational force of attraction between the earth and the sun provides the necessary centripetal force
Thus, Mev2/r = GMsMe/r2
v = GMsr
But v = 2πr/T
Thus 4π2r2 / T2 = GMs / r
Mass of sun Ms = 4π2r3 / GT2
Substituting the values and simplifying
Mass of the sun Ms = 4 × (3.14)2 × (1.5 × 1011)3 / 6.7 × 10-11 × (365×24×60×60)2
Ms = 2 × 1030 kg.
Ques. Which force is responsible for radioactive decay? (2 marks)
Ans. The weak nuclear force is responsible for radioactive decay
Ques. Which force decides the structure of galaxies? (2 marks)
Ans. Gravitational force decides the structure of galaxies
Ques. The change in the value of g at a height h above the earth is same as at a depth d below it. If h and d are compared to the radius of the earth. What is the ratio (h/d)? (4 marks)
Ans. Since, g at height h is given by
gh = gR2 / (R+h)2
= gR2 / R2(1+h/R)2
gh = g (1+h/R)-2
gh = g (1 – 2h/R) ……………………………. (For h < and similarly we have g at depth d – gd = g (1 – d/R)
but gh = gd
g (1 – 2h/R) = g (1 – d/R)
h/d = 1/2
Ques. While approaching a planet circling a distant star, a space traveller determines the planet’s radius to be half that of the earth. After landing on the surface he finds the acceleration due to gravity to be twice that on the surface of the earth. Find the ratio of the mass of the planet to that of the earth. (3 marks)
Ans. In case of the Earth, GMe × mre2 = mge
In case of the planet GMp × mrp2 = mgp
Dividing these two equations, we get
(Mp/Me) (r2e/ r2p) = gp / ge
But gp = 2ge
And rp = re/2
(Mp/Me) = 1/2
Thus the ratio of the mass of the planet to the mass of the earth is 1/2.
Ques. Why does a satellite not need any fuel to circle the earth? Is it possible to put an artificial satellite in an orbit such that it always remains visible directly over New Delhi? (2 marks)
Ans. The satellite does not need any fuel to circle the earth due to the gravitational force between the satellite and the earth providing the necessary centripetal force required to keep it in its orbit. No, it is not possible to put an artificial satellite in an orbit such that it always remains visible directly over New Delhi as it is not on the equatorial plane.
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