People were watching a movie showing a car driving inside a big cylinder on a vertical wall (see below a frame from this video obtained from www.aol.co.uk/2012/04/05). How would you explain this?
a) Impossible – some kind of film trick
b) The only way to do it would be to add some very strong magnets in the wheels and drive on iron wall. The attraction force between the magnets and the iron wall results in the friction force to be bigger than the force of gravity pushing the car down.
c) Most likely, there is a huge vacuum pump under the car, which sucks it to the wall and results in a friction force bigger than the force of gravity pushing the car down.
d) The car is moving at high speed so a centripetal force forcing it to drive in circle inside the cylinder results in the force pushing the car towards the wall. This force results in the friction force bigger than the force of gravity pushing the car down.