Final answer:
Gravity supplies the centripetal force needed for a roller coaster to traverse the loop at ideal speed; at higher speeds, additional normal force acts to maintain motion, while at lower speeds, the track's attachment provides necessary force. Magnetic propulsion can increase the speed and normal force exerted in loops.
Step-by-step explanation:
In amusement park rides with loop-the-loops, the centripetal force necessary to keep the car hugging the track is of critical importance. When the roller coaster car travels over the top of the loop at the ideal speed, gravity provides just enough force for this centripetal acceleration without any additional forces needed. However, when a car goes over the top faster than the ideal speed, it experiences normal force in the direction opposite to gravity because the track must exert an additional force to keep the car in circular motion. Conversely, if the car is slower than the ideal speed, gravity is not providing enough force to maintain the circular motion, and the car's attachment to the track supplies the additional centripetal force, which also acts in the downward direction towards the center of the loop.
To maximize a roller coaster's speed, engineers consider factors like wire coils and magnetic forces, which can propel the cars faster and increase the normal force when moving through a loop. In a scenario where magnetic propulsion is used, the coaster with the stronger magnetic force would tend to go faster, causing a greater normal force to act when the car passes the loop's peak.