As a kid I had some Hot Wheels tracks that I would set up in our basement. I used to run cars and marbles down those tracks for hours. I was a very basic set up, but still worthy of a lot of fun. I didn't have all the fancy parts, like my friend who had a loop for his track. I don't know about my friend, but I learned a lot about physics from that loop in his track. How high did the start of the track have to be for the cars or marbles to make it around the loop without falling? How fast did they have to go in order to keep from falling? We would adjust the track until the cars were going just fast enough to make it around without leaving the track. And for the record, the start needed to be just a bit higher than the top of the loop.
Well, it seems that now we can make it around these loops in real cars. Pretty impressive.