Question

The gravitational force between which two objects would be the most difficult to notice?

A. The moon and a water particle.

B. The moon and the earth.

C. The earth and the sun.

D. A water particle and an air particle.

Answer 1

D. The gravitational force is proportional to the product of the two masses (F = G m1 m2 / r^2). A water particle and an air particle have the smallest masses, so their mutual gravitational force is the smallest (and far below the forces in the other choices).