The analysis of friction in brake systems shows a complex dynamic dependence of friction and wear. Friction produces wear but wear affects the surface topography and by that the friction power itself. The wear in technical brake systems causes a dynamic equilibrium of growth and destruction of surface structures on the brake pad, carrying the friction power. This interaction between friction and wear generates a new dynamic friction law, which describes the effects on friction, wear and temperature on different time scales. For very slow processes the friction law reduces to the classical form, describing only the velocity and heat dependence of friction. For unsteady processes the dynamic friction law is able to describe and explain even complex measured friction events in brake systems.