What do the brakes rely on to stop a vehicle?

Friction between the brakes and wheels. The contact causes friction, causing work to be done. The faster the vehicle goes, the more energy there is in its kinetic store, so more work must be done to stop it. This means that a greater braking force is needed. A larger braking force means a larger deceleration. This can be dangerous because it can cause the brakes to overheat, and make the vehicle skid.