Two rods, ‘A’ and ‘B’, of the same weight and equal length, have different thicknesses. A boy, while playing with them on a beach, held them vertically on the surface of sand as shown in the figure. Which one of them will sink less? Explain.


We know that the pressure varies directly with the thrust and inversely with the area on which the force is applied. For equal amount of force, a smaller area would result greater pressure hence the rod ‘B’ will sink less than that of the rod ‘A’. It is because rod ‘B’ has more surface area.