Bernoulli's Principle

In 1738, Daniel Bernoulli plublished his book: Hydrodynamica. The book explained his theory of fluid machanics. He showed that when a fluid speeds up, its pressure drops. He was using water and liquids in pipes as well as lots of math to prove his theory. I found this fun depiction of his principle: When most people think of a sail, they assume the wind blows from behind and pushes it, perpendicular to the cloth. This is incorrect. Instead, the wind flows parallel to the sail, across the surface. But that leads to a new question: if the sail isn’t pushed, where does the force come from? It turns out a sail is actually a wing that uses lift to pull you forward, not a scoop that catches the air. The same physics that keeps a jet airplane in the air is what moves the boat. Because a wing is curved, air has to travel a longer distance as it blows across the front of the sail than behind it. To go a longer distance in the same amount of time, the airspeed over the front of the wing has to go faster. Faster air has lower pressure, so it basically creates a partial vacuum pulling you forward. This is called lift, or Bernoulli’s principle. This is why you can sail upwind, and why the sail is always at an angle to the wind, never directly in front or behind. You manipulate this angle with the rudder and keel to determine your speed and direction. It’s actually a bit more complicated than that, but fundamentally, a sail pulls, it doesn’t push. Check this vid from some NASA scientists that goes even deeper into the subject, 250 years later.