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Science Friday: It Shatters Windows and Controls Fluids; it's The Bernoulli Effect

Submitted by Tjadendevries on Fri, 04/30/2010 - 3:42pm


It Shatters Windows And Controls Fluids. It's The Bernoulli Effect

    The Bernoulli Effect is fairly simple to explain. A moving fluid exerts less pressure on the object that it's rushing past than a stationary fluid does. A large group of people rushing past will push a by-stander away with their rough elbows, sharp umbrella tips, and lit cigarettes. Someone standing by a uniformly flowing group of liquid or gas molecules will feel themselves lightly drawn into the stream.

    This isn't because the stream itself has an attractive force. The stream still exerts pressure on objects standing along its side. It's just that it exerts less pressure than the atmospheric pressure on the other side of the object. Because of the difference in pressure, the object will be pushed into the stream.

    An easy way to test this is in the kitchen. Turn on the faucet so that the water is flowing evenly. Then hold a spoon so that the outward curved side is in the stream of water. Instead of being pushed away, the spoon should be drawn into the rushing water. This is only mildly interesting, but regular readers will recognize that is possibly the only experiment safe enough that Io9 will actually recommend people testing it out for themselves. It'll only happen once. Go nuts.

    Those not completely riveted by this experiment can find more exciting demonstrations of the Bernoulli Effect. For example, it's one of the reasons that planes fly. Because the plane's wing is curved above and flat below, air rushes faster over the top than it does over the bottom. This creates a difference in pressure that helps lift the plane off the ground.

    Race cars use the Bernoulli Effect to stay on the ground. The placement and shape of fins on a race car force air to flow faster below them. This forces the race car down, onto the track, and keeps it from going airborne, a situation that would lead to terrible tragedy but really awesome photographs.

    Even nature gets a little piece of the Bernoulli action. One of the reasons that windows shatter during storms is the wind rushing by them. Since there is no wind inside the house, the still air exerts more pressure on the window than the wind rushing by outside does. The effect is the same as someone leaning all their weight on window glass. Eventually, the pressure gets to be too much, and the window shatters outward.

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