Question

A group of students are spending the afternoon by a pond. Kenny says that “The pressure on the surface of the pond must be the same as that on the surface of the little puddle next to me.” Eric says: “The pressure cannot be the same, since the surface area of the puddle is much smaller and so the pressure on the puddle must be larger.” Stan says that “there is much less air above the puddle, and so the pressure on the puddle must be smaller.” Who do you think is right? Explain.

Answer 1

Eric is right.  The pressure on the smaller puddle is larger.  Pressure exerted by a force and the area over which it acts are inversely proportional to each other.  Therefore, the pressure exerted by a force will increase, if the area over which the pressure acts decreases.  Similarly, the surface area of the smaller puddle is smaller.  Therefore, the pressurce acting on it must be larger.