A psychologist makes an experiment with a mathematician and a physicist. He puts a good-looking, naked woman in a bed in one corner of the room and the mathematician on a chair in another one, and tells him: "I´ll half the distance between you and the woman every five minutes, and you´re not allowed to stand up." the mathematician runs away, yelling: "in that case, I´ll never get to this woman!". After that, the psychologist takes the physicist and tells him the plan. The physicist starts grinning. the psychologist asks him: "but you´ll never get to this woman?", the physicists tells him: "sure, but for all practical things this is a good approximation."