Centre of gravity on Cornmarket

We saw this entertainer on Cornmarket in Oxford. This is obviously a very simple trick: you need to get your centre of gravity over the rope and then you balance... Very difficult in practice. First there is the distinction between centre of mass and centre of gravity. It depends what you are doing. If you are trying to accelerate something, then inertial mass becomes important and it is the centre of mass that you want. Here, we are interested in the weight, so centre of gravity will be a more sensible usage although I think they are in the same place. If the centre of gravity is not above the rope, there will be a perpendicular distance from the rope, which will act as a pivot, and the line of action of the man's weight. There will thus be a resultant torque which will make him spin one way and fall. The balancing act involves producing a movement to make an equal and opposite torque every time you wobble slightly.