Inverse-square law

Apparent brightness decreases with distance squared, so a quasar visible at large distance must have a very large intrinsic power output.

Field strength follows an inverse-square dependence on distance from a point mass, so doubling the distance reduces it to one quarter.

A quantity such as intensity or radiation flux falls in proportion to 1/r², where r is distance from a point source.

The magnitude of the force is given by F = Gm₁m₂/r², so the force depends on the square of the separation r.

The force is inversely proportional to the square of the separation r, so doubling r quarters the force.

The force is inversely proportional to the square of the distance r between the centres of the masses.