Kern E. Kenyon

Bernoulli Weather or Not

Thirty five day records of wind speed and atmospheric pressure, measured and recorded every two hours, were obtained on a ship that sailed from California to Japan along latitude 35 N in the spring of 1976. Time variations of two days, which can be seen in the raw data of both variables, were brought out more clearly by a two-step smoothing process followed by a subtraction to reduce both the lower and higher frequencies. Comparing the two similarly processed records shows that when the wind speed is relatively strong, the pressure is relatively weak, and vice versa, at the two day time scale. An argument is given that Bernoulli’s law was operating in those weather systems.

Fluid Reaction Force on Solids

Steady flow past a circular arc wing produces a vertical lift force, which has been calculated before, but it also causes two horizontal reaction forces, equal and opposite, due to Newton’s third law: the accelerated and decelerated flows act back on the top surfaces of the wing. Reaction forces are computed here and compared with the lift force. The magnitude of the two perpendicular forces are equal when the ratio of the maximum thickness of the wing is about 1/5 the length of the wing’s flat bottom surface. An example of an asymmetric wing is discussed and the net reaction force is calculated, which is always directed horizontally away from the top surface of the wing that has the greater mean slope. Based on these results,it is predicted that a surface ship should go more easily through the water if the bow were blunt and the stern pointed, just the opposite configuration of what is commonly found traversing lakes and oceans. Surface gravity waves are argued not to change this conclusion in general.