Third grader asks: how far to zero gravity?
My son Bradley asked how far away from the earth would one have to travel to no longer be effected by gravity? I thought I would be able to find a quick answer but have not and we would appreciate your expertise, as would his third grade classmates in Fishers, Indiana. Reply The formulas of gravity put no limit on how far it extends–it just gets weaker and weaker. At the distance of the Moon it is still strong enough to keep the Moon from running away. That was what gave Newton the idea that gravity was “universal”–that the same force which drops apples from a tree to the ground also holds the Moon in its orbit. The Moon is about 60 times as far from the center of the Earth as we on the surface are. Newton figured everything was pulled towards the center of Earth–and also that the force of gravity got weaker like the intensity of light when you move away from a lamp. At 60 times the distance, light gets 60 times 60 = 3600 times weaker, so Newton wondered–would a force equal to 1/36
