1. The problem statement, all variables and given/known data When you slam on the brakes your car decelerates but this is not constant as it starts at a higher value and then reduces. This has something to do with the coefficient of friction between the brakes and the discs, but what is it and what are the reasons for this? 2. Relevant equations Not applicable. 3. I am assuming that the coefficient starts high due to the brakes being cold but then drops off as the brakes and discs heat up due to the kinetic energy changing to heat energy. There must be another factor that changes the coefficient of friction to change the deceleration rate but I am not sure what. Is it the materials, the road surface, the force on the brakes dropping off?