I have found an equation in a physics text book im reading that leaves me completly stumped. It is about the co-efficient of friction, looks very simplistic but when i read it this equation looks very illogical. I probably don't understand it fully or something like that but I really need someone to please explain exactly how this equation works. The equation represents the co-efficent of friction, it looks simple enough but i have some concerns with it. u=Co-efficient of friction F= Force of friction R= Force pressing surfaces together u=F/R My problem with this equation is that its states that if the force pressing the surfaces together increases (say the force of gravity on a moving car increases) then that makes the Co-efficient of friction less as the force of friction would be divided by this increased force. But surely thats not true because if the force of gravity increased then logically the co-efficient of friction would increase with it. Please help and a Thank for your comments or whatever help you can offer.