The force of attraction between two unit point masses separated by a unit distance is called:
Answer & explanation
Correct answer: option 1
The correct answer is Option (1) → Universal gravitational constant
By Newton’s law of gravitation, two masses \(m_1\) and \(m_2\) at a distance \(r\) attract each other with a force \(F=\frac{Gm_1m_2}{r^2}\). Putting \(m_1=m_2=1\) and \(r=1\) gives \(F=G\): the universal gravitational constant is the force between two unit masses at unit distance. Its value is \(6.67\times10^{-11}\,\mathrm{N\,m^2\,kg^{-2}}\).
Why the other options are incorrect
Option (2) Acceleration due to gravity — Incorrect. The acceleration of a body falling freely near the Earth, about \(9.8\,\mathrm{m\,s^{-2}}\); it is an acceleration, not a force.
Option (3) Gravitational potential — Incorrect. The work done in bringing a unit mass from infinity to a point; it is energy per unit mass.
Option (4) Gravitational field — Incorrect. The force on a unit mass placed at a point, due to some other mass; it depends on that mass and the distance.