Final answer:
When parking a car facing downhill, the steering wheel should be directed toward the curb to ensure that it rolls into the curb and not into traffic if the brakes fail. This uses friction to prevent uncontrollable movement.
Step-by-step explanation:
When parking a car facing downhill, you should direct the steering wheel toward the curb. This action is in line with basic road safety rules and ensures that if the brakes fail, the car will roll into the curb rather than into traffic. The direction of the wheels helps to provide a physical barrier to prevent the car from rolling down the hill uncontrollably.
In terms of physics, this strategy makes use of friction and other forces acting on the stationary vehicle. If the car begins to move, the friction between the tires and the road should guide it towards the curb, minimizing the risk of an accident.
Additionally, using a parking brake is also recommended to further secure the vehicle against unwanted movement. However, turning the steering wheel towards the curb remains a critical step for safety.