Loop the loop at Zippos Circus

We went to see Zippos Circus in Ayr. Loved it! This the Lucius Team doing their Globe of Terror motorcycle act. There were 4 of them in there at once. Analysis of the Wall Of Death type bits to come but in this picture, there is a rider upside down inside the top of the globe. Centripetal force is (massxspeed squared)/radius. Centripetal force is a resultant force. In this case, it must be the difference between the rider's weight and the reaction force. At the bottom, reaction force must be bigger than weight. At the top, I think that the bike will have lifted off a bit so that the weight is bigger than the reaction. As long as the speed is big enough, there will still be a reaction force so the bike will stay in contact. I thought this was going to be easy to explain but it's not quite the same as the normal problems so I'll have to think further.