A porter carries the same 50kg sack of grain either on a thin metal rod or on a broad wooden plank kept on his shoulder. Why does the plank feel less painful?
(a) The plank distributes the same force over a larger area, so the pressure on the shoulder decreases.
(b) The plank is made of wood which absorbs most of the force, so almost no pressure reaches the shoulder.
(c) The plank spreads the weight and therefore halves the total force acting on the shoulder, making it less painful.
(d) The plank increases the distance of the sack from the shoulder joint; this larger moment arm reduces the pressure felt.