If RE is the radius of the Earth, then the ratio between the acceleration due to gravity at a depth r below and a height r above the Earth's surface (given r < RE) can be approximated as:

On Earth, g ≈ 9.8 m/s2. If an object is moved to a location where g = 0, its mass:

The force with which the Earth attracts an object is called:

Two stars of masses m and 2m at a distance d rotate about their common centre of mass in free space. Their period of revolution is: