Tag Archives: Bernoulli’s Principle

Bernoulli’s Principle

Daniel Bernoulli was a Swiss mathematician and physicist in the mid-1700s. He excelled in the fields of statistics and probability, but also was influential in applying mathematics to physical mechanics. Particularly, he is known for his work in fluid dynamics, now known as Bernoulli’s Principle.

bernoulliMost simply, Bernoulli’s Principle is a derivation of the conservation of energy. The sum of all the energies in a steady flow of a fluid (a gas or a liquid) must remain constant. So, if the fluid is forced to move faster, it creates an area of low pressure to compensate.

This principle may seem simple, but it led to the development of two very important machines in the 1900s: the carburetor and the airplane.

The carburetor is the precursor to modern automobile and aircraft engines. Using Bernoulli’s Principle to control the flow of fuel and air, it allowed automobiles and airplanes to control their speed and acceleration with relatively high precision. More efficient methods have since been designed, but without the basis of Bernoulli’s Principle, these machines would never have been developed in the first place.

bernoulli 1Additionally, Bernoulli’s Principle is critical in the design of airplane wings and allowing them to generate lift. The bottom of the wing is flat, while the top part is rounded. As the wing cuts through the air, the gas going over the top has a longer path to take, which requires it to move faster than the air underneath the wing. This creates a low pressure area on the top of the wing. The pressure difference between the top and bottom causes an upwards force to be exerted on the wing, allowing the airplane to fly. While this is not the only source of lift, it is an important factor that allows airplanes to work the way that they do!

The Physics Behind Curveballs

With the MLB All-Star Game happening, you might be wondering how curveballs and other pitches actually work. Well wonder no longer because Derrick has the answer for you! It all has to do with the 216 raised red stitches altering the airflow around the ball.

curveballs 1

 

If the ball leaves the pitcher’s hands spinning counterclockwise like above, the stitches are causing air to move faster above the ball than it does below. If you remember our post about Bernoulli’s Principle, you’ll know that this creates a lower pressure zone above the ball. That lower pressure causes a form of lift referred to as the Magnus Effect, keeping the ball from dropping as much on its way to the plate, delivering a fastball to the batter.

curveballs

If the pitcher instead twists their wrist in another direction, the Magnus Effect pulls the ball in the direction of lower pressure. Pitchers can use this to make balls drop to the ground quicker or veer off to the side, giving curveballs their namesake.

Bernoulli’s Principle Will Leave You Breathless!

What sorcery is this!? Science it turns out! This is a great example of Bernoulli’s Principle! In short, this states that moving air has a lower pressure. Imagine trying to dig a hole in a pool of water: as soon as some of the water gets moved out of the way, the surrounding water rushes in to take its place. Air does the same thing: whenever it moves, the lower pressure draws air in around it!

The cup and straw demonstration shows this nicely, and it’s also a great experiment to try at home! By taking each apparatus and blowing into it, we can see there is a pretty huge difference.

difference

Inside the cup, air is moving quickly. This causes a lower pressure inside the cup than outside, and air that tries to fill up the space suctions the balloon in place. Alternatively, the cup with holes in the sides allows the surrounding air to help out. Very similar to the Bernoulli Bag, nearby air joins in creating a larger column of air that can lift, and even suspend, the balloon.

bernoulli-loop

We know this looks like a trick, because it’s hard to tell from watching that he is exhaling vigorously in both cases. If you don’t believe us, definitely try it yourself!  Of course, it is possible to hold the balloon into the cup by inhaling, but it’s actually more difficult to suck up the balloon from a short distance away! The difference in pressure from blowing fast moving air into the cup is more effective at sucking up the balloon.

While Bernoulli’s Principle can be tricky to understand, it is very important! The fact that fast moving air has a lower pressure is one of the primary ways that airplanes are able to generate lift! The air going over the wing actually goes faster than the air below, which you can see in this very cool shot from a wind tunnel!

wing-wind-tunnel

Credit: Holger Babinsky, University of Cambridge

Levitate a Soda Can

Did you know that Bernoulli’s principle is a statement of conservation of energy? The sum of kinetic and potential energy is constant in every closed system. In fluid dynamics, potential energy is an expression of the pressure within a volume of liquid or gas. When a fluid moves faster (its kinetic energy increases), pressure (potential energy) must decrease to compensate.

uOregonBernoulli

Image credit: University of Oregon

This coupling of behaviors creates fun scientific results! We’ve explained before how to levitate a beach ball with a leaf blower. Today, we’re scaling Bernoulli’s principle down to tabletop size for a super-doable DIY experiment. All you need is an empty soda can and a mug big enough to contain it.

CokeJump

Place the can inside the mug and blow air into the gap between the two containers. Your breath moves faster than the surrounding air, so it creates an area of low pressure around the sides of the can. Stagnant air trapped underneath the can expands to fill the partial vacuum, pushing the can upwards. With a little practice, you’ll be able to jump the can from one mug to another!

Written By: Caela Barry  

Bernoulli’s principle: Supercells & Airplanes

In strong supercell thunderstorms, wind moves upwards at over 90mph. Fast-moving air creates an area of low pressure, or a partial vacuum. Nature abhors a vacuum, so nearby air rushes in to join the updraft. This skyward flow can be powerful enough to suspend grapefruit-sized hail.

Thunderstorm

The tendency of a speeding air current to suck in surrounding air molecules stems from the same idea that gets airplanes off the ground: Bernoulli’s principle. The faster a fluid moves, the lower its pressure. Airplane wings have more pronounced curves on the top side than they do on the bottom, so air follows a longer path, and moves faster, above the wing than below. Higher pressure from underneath the wing translates to an upward force– that’s lift.

Aircraft and thunderstorms provide some of the most dramatic examples of this concept, but it’s also surprisingly easy to explore at home or in class. All you need is moving air and something to reveal its motion! A long, narrow bag and a working set of lungs are the perfect tools. Try to blow up eight feet of plastic bag like you would a balloon and you’ll find yourself struggling for air. Instead, hold the bag’s opening ten inches from your face, and blow into it across the gap. What’s the difference?

BernoulliOneBreath

When your breath travels through a volume of air before reaching the bag, Bernoulli’s principle does most of the work for you! Your exhalation is a fast flow, so it creates a sink of low pressure moving into the plastic bag. Nearby air rushes in to fill the partial vacuum, and before you know it, the bag is fully inflated.

Firefighters clearing smoke from buildings take advantage of Bernoulli’s principle in almost exactly the same way. A fan placed directly in a door or window will move air through the structure. Set the same fan a short distance back from the opening, and it pulls in more air, getting the job done faster.

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