Lets say I have a brick of mass m, length L and height h which is resting on a table in such a way that L - r of it is in the air (not on the table) and the rest is on the table. What is the minimum value of r if the brick is not to fall? Just by looking at this, it seems the minimum value is L/2 right? Suppose this is the situation. Let N be the normal force on the brick. Clearly N = mg. If I calculate the torque about the edge of the table, I get NL/4. Since the brick isn't falling, the torque is zero, but that would imply that NL/4 = 0! How is this possible? Does this mean the brick falls? Suppose r > L/2 (so more than half of the brick is on the table). Calculating the torque about the edge of the table again gives me mg(L/2 - r). If the torque is zero (which I hope it is), then r = L/2. This clearly doesn't make any sense. What is going on here?