Hi, I was just about to finish the chapter on gravity and gravitation in my physics book when I came across (in another physics book) an example problem that showed a motorcycle stuntman riding on the inside walls of a right verticle cylinder. I wondered how it was possible for him to to around the cylinder without falling, gravity acts down on him, and there is friction, but the obviously the friction cannot be great enoght to support his weight when he is horizontal like that. It says hes on a cylinder of radius 15meters. So what I did was use the orbital velocity equation [tex]sqrt(g*r)[/tex], where g is 9.81m/s and R is 15m, and go an anwser of 12, which is what the book said the anwser was. I am interested in knowning two things. First, if I calculated the anwser correctly or got a similar anwser by chance. Second, I would like an explination on the physics behind that kind of situation. I can kind of see how he would have an orbital velocity, but when we derived the orbital velocity equation, we assumed that we were throwing a rock faster and faster until fell at the same rate the earth curved away from it. Here, the motorcycle man isint really falling around the earth continually is he, since he is going around a verticle tube over and over again.