Final answer:
When parking on a downgrade with a curb, the wheels should be turned toward the curb. This safety measure ensures the car will roll into the curb and stop if the brakes fail, a concept related to forces applied to moving objects such as centripetal force in turning vehicles.
Step-by-step explanation:
When parked on a downgrade with a curb, you should turn your wheels toward the curb. This is a safety measure to prevent the car from rolling into traffic if the brakes were to fail. Turning the wheels toward the curb will cause the car to roll into the curb and stop, instead of rolling down the street. This same principle is similar to the thing that happens when forces are applied to objects in motion, such as the centripetal force acting on a car that keeps it moving in a curve instead of in a straight line due to the friction between the tires and the road. In parking on a downgrade, you're essentially setting up a failsafe that uses gravity and the position of the wheels to provide friction and 'catch' the car against the curb if necessary, much like the friction between tires and road provides the force necessary for a car to turn on a curve.