The weight of a person at the equator, as determined by a spring balance is 715N. By how much does this differ from the true force of gravitational attraction at the same point? Assume that the earth is spherically symmetric. I've tried many different forumla's but can't seem to get the right answer, I thought that it might be the same but I guess it isn't. The next thing I tried was getting their mass (715/9.8) and plugging it into F = -gmM / R^2 but that didn't work either...any other ideas?