Final answer:
When you park on a hill, the direction your car will roll if the brakes fail is determined by the combination of static and kinetic friction.
Step-by-step explanation:
When you park on a hill, the direction your car will roll if the brakes fail is determined by the combination of static and kinetic friction.
Static friction is the friction between two surfaces that are not moving relative to each other, while kinetic friction is the friction between two surfaces that are moving relative to each other.
When the brakes fail and the car starts to roll, the static friction between the tires and the road prevents the car from immediately sliding down the hill. However, as the car starts moving, the static friction gives way to kinetic friction, which acts in the opposite direction of the car's motion, causing it to roll in the direction it was pointed.