look here: http://www.mut.ac.th/~physics/PhysicsMagic/wall.htm" scrolling to the motorcycle section, my question is, why is it that you cannot consider the point of contact of the motorcycle with the wall as a pivoting point? I have done some calculations, and this leads to a physically nonsensical answer. I recognize that any line of force not acting through an object's centre of mass would produce a torque about an axis through the centre of mass,and that would indeed lead to a coherent answer, but my problem is, why can the point of contact NOT be considered a pivot? The motorcycle would rotate about that point after all. Another point to clarify, the principle of moment states: For rotational equilibrium, the sum of the clockwise moments about any point must be equal to the sum of the anti-clockwise moments about the same point. Does 'any point' refers literally to any point within the frame of reference, of simply any point that can act as a pivot only? Thanx.