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On earth, two objects of different masses fall at the same rate. However, in space, larger masses exert greater gravitational attraction than smaller masses. This seems inconsistent. What am I confusing? - DD, Miami, FL
On your mark, Get set, Go!
If an elephant and a mouse were dropped from the same point in the sky, at the same time, which one would reach the ground first? (neglect air resistance)
Answer: They would fall at the same rate and would reach the ground at the same exact time!
There is no inconsistency. When you drop two objects on earth, they do fall together, but that doesn't mean that they both exert the same force on the earth. The object with the larger mass attracts the earth more strongly than the one with the smaller mass. Similarly, the earth attracts the object with the larger mass more strongly than it attracts the one with the smaller mass-the more massive object weighs more. The reason why they fall together is that while the more massive object weighs more and is pulled downward harder, it is also more massive and thus harder to accelerate. A stronger force is needed to accelerate it downward so that it keeps pace with the smaller mass as the two fall. Its larger weight perfectly compensates for its larger mass and the two objects fall at the same rate. Whether on earth or in space, more massive objects exert stronger gravitational forces. It's all consistent.
Answered by Louis A. Bloomfield of the University of Virginia