Tag Archives: Bernoulli

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!

Curveball Science

The Magnus effect allows pitchers to throw curveballs, soccer players to bend kicks around defenders, and golfers to launch drives along near-triangular flight paths. This fun physics phenomenon relies on the difference in relative airspeed at various points on the surface of a round object.

GordonDamGif

Viral video captures the Magnus effect in action, 2015. Credit: YouTube channel How Ridiculous. Full footage: https://www.youtube.com/watch?v=QtP_bh2lMXc.

Picture a ball moving through the air while spinning. For the ball to experience a net force, its axis of rotation must be oriented so that some points on the ball’s surface move in the same direction as its trajectory (let’s name one of these points A) while some move the other way (we’ll call an example of this type B).

MagnusDiagram

At point A, the air dragged along by the ball’s surface and the air farther away rush past each other in opposite directions; at point B, they move in the same direction, although one still moves relative to the other (unless rotational speed and flying speed are perfectly matched). This is a bit like the difference between two cars going in opposite directions on the highway and a car in the fast lane passing one in the slow lane.

Like a boat traveling through water, the ball leaves a wake behind as it cuts through the air. The differences between relative airspeeds around a rotating ball cause its wake to pull to one side, resulting in an asymmetrical imbalance of air pressure. This lopsided push bends the ball’s path as it travels.

MagnusGif

A DIY-friendly demonstration of the Magnus effect. Unlike the basketball, which had a backspin as it fell down the dam, the paper roll’s front edge is spinning along with its trajectory. This results in a backwards arc.

The Magnus force affects cylindrical objects in a similar way. Try this at home with a sheet of paper, rolled up and taped into a cylinder. Allow the paper tube to roll off the edge of an angled surface to give it a uniform spin, and watch its path curve!

Written By: Caela Barry

Fire Tornado!

Tornadoes are born when extreme weather circumstances come together. Their short, destructive lives are still not fully understood, but one leading theory goes like this: sometimes, winds at different altitudes blow at different speeds, rolling the air between them into a horizontal, rotating cylinder. If a supercell thunderstorm is nearby, the spinning column can be pulled into the maelstrom. Once the tornado is vertical, its lower end has the potential to touch down and wreak havoc on Earth’s surface.

West Texas wildfire

West Texas wildfire. Image credit: Texas Forest Service.

In a real supercell, swirling updrafts are created by variations in temperature, pressure, and wind speed in the storm area. In this experiment, we simulate updraft conditions by physically pushing the air into a rotating column formation using a window screen rolled into an open-ended cylinder. Without the screen (and the wind it generates), the spinning fire doesn’t do anything especially interesting. That’s because of Bernoulli’s principle: the faster a volume of fluid moves, the more neighboring molecules are sucked into the breeze. By giving the air a push, we draw extra oxygen in towards the flame.

FireTornadoGif

Fire tornadoes are spectacular in the lab, but you don’t want to see one in nature. These twisting ropes of flame have played a tragic role in several of the greatest conflagrations in human history. From Chicago to Peshtigo to Tokyo and beyond, they’ve spread blazes with devastating speed and blocked victims from reaching safety in nearby bodies of water.

At least one team of researchers is working towards harnessing the power of the fire whirl for practical purposes. Hot, clean-burning blue fire tornadoes show potential as a tool for improved oil spill cleanup.

As with any experiment involving combustion, check in with an adult, keep a fire extinguisher on hand, and exercise caution if you decide to make a flaming tornado at home. We used a turntable with a heat-safe covering, a non-flammable window screen stapled into a cylinder, duct tape, a glass flask, and a few ounces of 99% isopropyl alcohol to create our fire whirl.

Written By: Caela Barry

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