Hi Ray,

If you haven't already, you may want to watch this video and the two following videos in the playlist: https://www.khanacademy.org/science/physics/centripetal-force-and-gravitation/centripetal-acceleration-tutoria/v/loop-de-loop-question

Essentially, the car is falling down, it's just moving fast enough that it falls in the shape of the track. If the car doesn't reach the minimum velocity (like Sal calculates in the above videos), the car would fall down once it gets close to the top.

I hope this helps!