Suppose the force of gravitation between two equal masses is F. If eac

Suppose the force of gravitation between two equal masses is F. If each mass is doubled keeping the distance of separation between them unchanged, the force would become

F
2 F
4 F
<img src="https://latex.codecogs.com/svg.latex? rac{1}{4}F" title=" rac{1}{4}F" />
This question was previously asked in
UPSC NDA-1 – 2016
According to Newton’s Law of Universal Gravitation, the force of gravitation (F) between two masses (m₁ and m₂) separated by a distance (r) is given by the formula:
F = G * (m₁ * m₂) / r²
where G is the gravitational constant.
Initially, we have two equal masses, let’s call them m. So, m₁ = m and m₂ = m. The force is F = G * (m * m) / r² = G * m² / r².
Now, each mass is doubled, so the new masses are m₁’ = 2m and m₂’ = 2m. The distance of separation (r) remains unchanged.
The new force (F’) is:
F’ = G * (m₁’ * m₂’) / r²
F’ = G * (2m * 2m) / r²
F’ = G * (4 * m²) / r²
We can rewrite this as:
F’ = 4 * (G * m² / r²)
Since F = G * m² / r², we have F’ = 4 * F.
The force becomes four times the original force.
The gravitational force between two masses is directly proportional to the product of their masses. If both masses are doubled, their product becomes (2m) * (2m) = 4m², quadrupling the force, assuming the distance remains constant.
The gravitational force is also inversely proportional to the square of the distance between the centres of the masses. If the distance were, for example, doubled instead of the masses, the force would become F/4.