Basic Concept of Bernoulli's Principle

Bernoulli's Principle describes the relationship of the speed and pressure of a fluid. As the speed of a fluid increases, the pressure of the fluid decreases.

There are two types of situations in which the Bernoulli's Principle is applied, incompressible and compressible fluid motion. In the above image, the image of airfoil shows the fluid motion of the air over the wing. This shows incompressible fluid motion.

Incompressible Fluid Motion is when an object is interacting with a fluid with the object's outside surface. And in the above image, because the top of the airfoil has a greater surface area than the bottom, the fluid flows faster over the top of the airfoil than the bottom. 

You can also experience this by putting your hand out the window during a car ride- if you tilt your hand with your thumb pointed directly into the wind, you can feel the air over your hand split with the faster air on top. Likewise, if you tilt your hand with your thumb pointed up or down, you feel the pressure of the air building on the facing surface, and it either pushes your hand down or produce lift.

Compressible Fluid Motion is when the fluid is inside an object that compresses the fluid to increase/decrease pressure and in turn affects the speed of the fluid. The above image shows the motion of the fluid compressed from a wide diameter into a narrowing diameter, increasing the pressure of the fluid and decreasing the speed.

One way to think about compressible fluid motion is how you would drink Boba Tea with Tapioca Pearls. Normally, you have a wide-diameter straw for the size of the pearls. When you sip your Boba Tea, you may have to suck on the straw with more of a vacuum (opposite of pressure) to get the pearl to travel up the straw faster. Otherwise, the pearls block delicious milk tea from moving through the straw.

---