We’ve all heard that Bernoulli’s principle is the reason that aeroplanes fly.
This physical phenomenon has been illustrated in different ways and described endlessly, but it’s still difficult to visualise.
A simplified explanation goes like this: The aeroplane’s wing is teardrop-shaped. Air that flows over the top of the wing has to travel a longer distance than the air that flows below the wing, so the air above has to move faster. This pulls air molecules farther apart, which means they put less air pressure on the top of the wing than the bottom.
The upward force of denser air below the wing produces lift:
Sometimes it’s hard to believe a little quick-moving air is really all it takes to lift it up a big, hulking aluminium tube in the sky (especially if you’re inside one). But the principle is easily demonstrated using just a piece of paper and your mouth.
I saw this trick on the “How to make a paper aeroplane” episode of Going Deep With David Rees. The show goes into extreme detail to explain how to do simple things like making a paper aeroplane or opening a door. During the episode, Rees visits the NASA’s Armstrong Flight Research Center in Edwards, California, and gets interrupted by engineer Red Jensen, who shows him this neat trick.
By blowing over the top of a piece of paper you can demonstrate Bernoulli’s principle. As Rees notes, “I’m totally about to understand what flying is! OK, go!”
“What we want to do to simulate a wing is to accelerate air over the top and have relatively still air under the wing,” Jensen said. To do this, blow over the top of a piece of paper held loosely from one end.
When the air moves quickly over the paper it creates lift, just like an aeroplane wing does. You’d think blowing on a piece of paper would push it away from your mouth but actually it lifts it up because of the faster-moving air above the sheet.
There’s some debate as to whether this actually shows Bernoulli’s principle, or if it’s another physics principle being applied, but it’s still a cool demonstration.
“Wait, so the aeroplanes that have jets, the jet doesn’t lift the plane?” Rees explains. “It just gets it going fast enough to trick the air into lifting the plane? That’s how jets work?”
See the full clip, from Going Deep with David Rees:
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