I am kind of an arm chair layman, The following is just my own curious mind working furiously on something I know I don't completely understand, and yet want to. It seems to me that just about every piece of matter is made up of mass, and therefor has some level of electromagnetic and gravitic atttraction. So, techncially, when you talk about gravity, shouldn't the calculation amount to the Force of Gravity minus the Force of Electromagnetism? And vice versa when you are looking for the Force of Electromagnetism? And general attraction is the combination of both? I realize Gravity is a much less powerful force than Electromagnetism at the atomic and sub-atomic levels, but it just seems to me that this is part of why their equations are so similar.