Hi, I was wondering about the difference between mass and charge. As far as my understanding goes, these are just some names we've given to these 2 quantities of "stuff" that determines the strength of the field each one causes in the space around it. However, I was thinking about Newton's equation that comes in handy for all sorts of problems, F=ma. If we increase the mass of an object, then all other things being equal, it will be more difficult to change its state of motion. On the other hand, there is no F=Qa. What I mean by that is, as far as I am aware, you could put as much charge onto that object as you wanted and, all other things being equal, it would be no harder to change its state of motion. So, my question is, why is this the case? why does mass seem to "drag" through "empty" space (i know empty space isn't strictly empty) but charge does not? I can't help feeling this is a bit of an ignorant question, but I've gone through 3 years of my 4 year physics course and this hasn't been covered in any way and I can't think of anything obvious I've overlooked. Thanks.