Final answer:
In the event of brake failure while going down a hill, pump the brakes, use the emergency brake, shift into a lower gear to engage engine braking, and avoid panic. These measures are practical and immediate as opposed to scientific methods that study braking mechanics.
Step-by-step explanation:
What to Do if Brakes Fail While Going Down a Hill
If your brakes fail while you're going down a hill, the first thing you should do is not panic. While the method of driving at 50 mph and then applying the brakes to record the time or distance it takes to stop the car is a way to gather scientific data on braking, it is not a practical solution in an emergency situation like brake failure. Instead, you should immediately try to pump the brakes to build up more brake fluid pressure. If pumping the brakes doesn't work, your next step is to gradually apply the emergency brake while holding the release button or handle to avoid locking the wheels and maintain control. Additionally, shift into a lower gear to engage engine braking, which helps to slow the car down without using the brakes.
Understanding the science behind braking, such as the conversion of gravitational potential energy into increased internal energy of the brake material and the role of friction, is beneficial. However, during an actual brake failure, practical safety measures take precedence. As explained in the context of trucks, using brakes to control speed transforms potential energy into heat in the brake material, but the mass disparity and rapid temperature rise can make this process ineffective in cooling brakes sufficiently during continuous use, such as on a long descent. Moreover, switching to lower gears allows the engine to absorb some kinetic energy, thereby assisting in slowing down the vehicle.
Regarding the relationship between static and kinetic friction, it plays a role in how a car stops smoothly. As you come to a stop, easing off the brake pedal allows the static friction (which prevents movement) to take over from the kinetic friction (which allows sliding), resulting in a less stop.