Place a ping pong ball into the opening of a small plastic funnel. Now blow through the small end to try to blow the ball out of the funnel. Any luck? Blow harder. Still no luck. OK bring out the big guns. Get a shop vacuum cleaner that can be hooked up backwards. Put the hose into the exhaust end so that it blows air out rather than sucks it in. That should blow the ball out. Stick the funnel tightly into the hose and try to blow that ball across the room. Won't work. The ball will bounce around a little but the blast of air will not be able to blow it out the large end of the funnel. Paradoxically the airstream that should blast the ball across the room seems to grasp it tightly into the funnel. So tightly that you can slowly turn the funnel upside down and watch that little ping pong ball seemingly defy gravity as well as the strong air blast. What's going on here?
Curve Balls in Baseball
Now lets move on from ping pong to baseball. A pitcher occasionally tries to fool the batter into a strike by throwing a curve ball. It seems to be heading straight into the strike zone but veers off at the last minute. STRIKE! How do they do that?
Airplanes
After the game the away team flies home (at least in the big leagues). Several hundred people sit in a large metal cylinder which again seems to defy gravity by soaring to 35,000 feet on a wing and perhaps a prayer or two. What holds it up?
Bernoulli's Principle Explains Why
These three apparently unrelated questions have the same answer: Bernoulli's Principle. They have moving air in common. In the 18th century, Daniel Bernoulli discovered that in a stream of air (or other fluid) the pressure is inversely related to the speed, if the elevation does not change. As air moves faster its pressure drops.
The airplane wing is designed so that the top is curved and the bottom is flat. Taxiing down the runway, the air blowing over the top of the wing travels faster than the air blowing underneath. The faster air has a lower pressure, so the greater pressure on the bottom of the wing pushes the plane up. When it gets going fast enough this lifting pressure exceeds the downward gravitational force. The plane soars.
To throw the curve ball the pitcher spins the ball. Because of this spinning an imaginary ant hanging onto a perfectly smooth ball for dear life would feel faster wind on the side of the ball spinning toward the batter and a slower wind on the side spinning back towards the pitcher. The different wind speeds on a smooth ball would cause a pressure difference. In a real baseball the seams carry some air with them so that the lower pressure and direction the ball curves is the opposite of what would be predicted for a perfectly smooth ball. Either way, the ball curves away from the strike zone just after luring the batter into swinging.
Blowing air between the inner cone of the funnel and the ping pong ball also produces a lower pressure that allows the still air on the other side of the ball to mash it into the funnel. A faster blast of air serves only to increase this effect.
The real world is of course complex, so in these examples there can be other effects at work in addition to Bernoulli's principle. For example, the angle at which the airplane wing is tilted also affects the lifting force.
Fundamental Principles in Physics
Part of the beauty and appeal of physics (and other sciences) is its economy. When physicists find one principle or theory that explains a large number of unrelated effects, they know they have a keeper. They have found a fundamental underlying principle. Aesthetically we prefer one basic principle or theory that explains hundreds (or more) of apparently unrelated phenomena to hundreds of different theories. Physics has a reputation for being a very difficult subject. But in reality it is among the simplest of the sciences. There are a only handful of very fundamental principles of physics. A good high school physics class can pretty much cover them all. More advanced classes simply apply the same principle to more complex situations. Yet these few principle can explain all the physical phenomena we see in our universe. The details are often complex but the basic principle is usually relatively simple. Bernoulli's Principle provides a good example of a single fundamental idea explaining a wide range of effects. Can you think of other Bernoulli effects?
Bernoulli Effect While Driving
Bernoullis Principle and Storms
https://suite101.com/article/bernoullis-principle-examples-a15812
