This isn't so much a question specifically as a point that came up in my mechanics class... so sorry if I'm posting it in the wrong place! In a basic mechanics class; we were finding the frictional force on a box by thinking about someone moving it by pulling an attached string. Someone in the class asked if where the string was attached made any difference to the movement; so my teacher went off on a rant about this being the difference between maths and physics- that maths uses perfect models and physicists want to deal with what actually happens (fair enough). He then went on to say that 'in maths we model the box as a dimensionless point, or 'particle'.. physicists deal with the fact it isn't by replacing it with a string' and then gave an extremely basic approximation of what a string is supposed to be. Now I'm sure most people on here know more about string theory than I do; but is that not the most ridiculous explanation of why it is needed that you ever heard??