I'm trying to explain Bernoulli's principle (in the context of flight) to an audience that doesn't have a physics background. So I'd like to avoid mentioning technical concepts as much as possible.
The part I'm specifically struggling to explain is why an increase in air velocity necessarily results in a decrease in air pressure. I could go down the path of explaining that an increase in velocity results in an increase in dynamic pressure which, due to the conservation of energy, must be met by a corresponding decrease in static pressure. But I'm looking for a more practical explanation that is easier to conceive.
So instead, I want to say the following:
The air over the wing travels faster than the air under the wing (I have already explained why this must be the case - Continuity Equation). There are two consequences of this:
- The molecules flowing over the wing hit the wing at a shallower angle since they have more forward motion. Since the pressure exerted by a fluid on a container is basically the sum of the forces by all the small collisions of the fluid's particles, this results in less pressure being exerted on the top of the wing.
- The molecules spend less time over the top of the wing (because they're traveling faster) and therefore have less opportunities to strike the upper surface of the wing. For the same reasoning above, this results in a less pressure being exerted on the top of the wing.
To play devil's advocate, someone might say "Yes, but you're missing one point which is that the molecules traveling above the wing are traveling faster. So while they may hit the wing at a shallower angle and less frequently, when they do hit the wing, they will hit harder and therefore exert more pressure".
So two questions:
- How do I address that counter argument?
- Are there any glaring holes or flaws in my overall explanation?