Final answer:
A person experiences a gravitational force downward and a centripetal force for circular motion while upside down on a roller coaster loop. An additional normal force acts upwards if the coaster is faster than the ideal speed and downwards if it is slower.
Step-by-step explanation:
For a person riding a roller coaster who is upside down at the top of a loop-the-loop, several forces are experienced:
- The person experiences a gravitational force pulling them towards the center of the Earth.
- The person experiences a centripetal force required for circular motion, which, at the ideal speed, is provided entirely by gravity.
Now, depending on the speed of the roller coaster as it goes over the loop:
- (a) If the car goes over the top at faster than the ideal speed for gravity to provide the necessary centripetal force, then the person will also feel an upward normal force from the seat pushing against them.
- (b) If the car goes over the top at slower than this speed, the normal force will act downwards, as the seat will push down on the person to provide the additional necessary centripetal force.