Wind, Water and Mr Bernoulli

The land’s wind shadow can be seen in the smooth water nearest the foreground of this picture of Nutbourne Marshes. This is an effect sailors, particularly dinghy sailors, will be very familiar with. It is the same effect that causes a build up of ice, sand and dust deposits on the lee side of obstacles on land. It is not usually quite as simple as the object getting in the way of the wind though, because of something called Bernoulli’s Law.

It is one of those laws that features a lot in our lives, but gets little credit. It helps chimneys to work properly and aircraft to fly. It causes the wind to accelerate as it travels over a curved surface and then decelerate as it reaches the other side. It probably deserves more credit as it is this effect that allows boats to sail into wind, a completely different physical process from downwind sailing where the boat is pushed along by the wind.

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