What is "Bernoulli's principle"?
Bernoulli's principle definitely has to do with aeroplanes. Bernoulli was around about 100 years ago. Now, he did not invent this he just discovered it. It was called Bernoulli's principle named after him. These are not exactly Bernoulli's words, but here's his principle: basically he said that where there's moving air there's low pressure. Okay, where there's moving air there's low pressure. Now, a couple of ways to demonstrate that: this is a simple little plastic tube and in the end I have a golf tee. The golf tee has been modified. There is a hole that has been drilled in it so air can come out. So, what I'm going to do is take this ping pong ball, which is very light, and I'm going to hold it over that hole and blow air through there, and I want you to watch what happens. That ball stayed up in that column of air, and it stayed in there because of Bernoulli's principle. Now, he said where there's moving air there's low pressure. The air hits the bottom of the ping pong ball and it goes all around the sides of the ping pong ball, so all around the ping pong ball we have moving air which is low pressure. Then, all the other air in the room around it is high pressure. So, if the ball falls one way the high pressure pushes it back. If it falls another way high pressure pushes the ball back. So, Bernoulli's principle works very well in explaining how that works. We also have this; a corrugated tube. Now this works together in showing two things; it shows Bernoulli's principle and also sound. This has a corrugated construction and as air goes through there the air will be vibrating; oscillating against the sides and making a sound. Now, when I spin this around in the air (let me just show you slow motion wise) you can see the end of the tube actually moving through the air. So, in reality we have moving air right here, and where there's moving air there's low pressure. As you spin it around, the high pressure in this room tends to want to fill that void. Since some of the air actually goes in to the bottom of the tube (well, as it travels through the tube) it makes a sound and that's how we can tell air is going through the tube. So, here we go with Bernoulli's principle making a tube sing. Cool huh? That's Bernoulli's principle remember; where there's moving air there's low pressure.
