The biomechanics of surfing, like many sports, is complicated. To provide some insights into pressure forces (which is related to our discussion of buoyancy in lecture), let’s approximate a surfboard that is 177 cm long, 46 cm wide, and 5.3 cm thick as a rectangular block. Consider the situation in which a surfer sits on the board while waiting on a wave such that the board is completely submerged below the water surface in a horizontal position, as shown below (not to scale). Clearly state any assumed fluid properties.

  

a. Calculate the pressure at the top of the surfboard, e.g. at a distance 30 cm below the air-water surface.

b. Calculate the pressure force, e.g. force due to pressure, of the water on the top surface of the surfboard. In what direction does it act?

c. Calculate the pressure at the bottom of the surfboard, e.g. at a distance 35.3 cm below the air-water surface.

d. Calculate the pressure force of the water on the bottom surface of the surfboard. In what direction does it act?

e. Determine the net pressure force on the surfboard. In what direction does it act?

f. What force could the submerged surfboard support?

g. Divide the net force value (answer in part e) by the volume of the surfboard (include units). Is there any physical significance to this, e.g. does this match the value of a fluid property you used in parts (a) and (c)?

5.3 cm 177 cm 30 cm Air Water