Braking
Brake pads apply a frictional force to the wheels in order to slow the vehicle down.
Via Newtons 3rd law, we know that the wheel (or rather the rotor, a disk attached to the hub and wheel assembly) is going to oppose this frictional force.
Due to the fact that the rotor and wheel assembly are fixed, we know that the torques experienced by each part will be equal [3]
[see in Tyres].
Energy conservation in Braking
When a car applies its brakes, all of its kinetic energy lost whilst slowing down must be transferred elsewhere as energy cannot be created or destroyed[4]. This is usually in the form of heat through the brake pads and rotor. Drivers prior to the race will warm up their tyres to their operating temperature as they are less efficient at low temperatures (see tyres and temp). However, they will also degrade too quickly if they exceed their operating temperature [5].
[6]
Cooling systems
Cooling systems are used to reduce temperatures and ensure that the brakes are kept at their optimal operating temperature. These can include liquid cooling systems (although these are forbidden in F1), where a cool liquid is passed over the brakes to absorb heat and thus reduce the temperature of the brakes. In F1 air ducts are used which channel air over the brakes to ensure a constant air flow over the braking system. In the image, 1 is a small inlet which allows cool air to pass directly over the brake calliper (the part which applies the frictional force to the rotor), 2 are the outlet perforations for the rotor from the larger inlet indicated by 3 [8].
[7]