The math around the windbag or Bernoulli bag experiment

In summary, the conversation discusses the math behind an experiment involving the mass flow rate of air coming out of someone's mouth and going into a bag. It is related to compressible flow and the explanation involves the reduction of pressure due to high velocity air, causing surrounding air to also enter the airbag. The speaker is seeking an explanation using equations, math, and physics or guidance in finding such an explanation.
  • #1
dillmon
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What is the math behind this experiment? If the mass flow rate of the air coming out of the guy's mouth is M1, then what is the mass flow rate, M2, of of the air going into the bag?

I know that this is related to compressible flow. The explanations I have found on the internet are that since the pressure reduces because of the high velocity air, the surrounding air will also go through the opening of the airbag. I would like to see an expiation using equations and math and physics, or at least be pointed in the right direction. Thank You.
 

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  • #2
 

1. What is the concept behind the Bernoulli bag experiment?

The Bernoulli bag experiment demonstrates the principle of Bernoulli's equation, which states that as the speed of a fluid (such as air) increases, its pressure decreases. In this experiment, the bag is filled with air and the opening is sealed. As the bag is squeezed, the air inside is forced to move faster, resulting in a decrease in pressure and causing the bag to expand.

2. What materials are needed to conduct the Bernoulli bag experiment?

The materials needed for this experiment include a plastic bag (such as a sandwich bag), a straw, and a rubber band. Optional materials include a ruler and a stopwatch for measuring the expansion rate of the bag.

3. How does the size of the straw affect the results of the experiment?

The size of the straw does not significantly affect the results of the experiment. As long as the straw is small enough to fit through the opening of the bag and create an airtight seal, the principle of Bernoulli's equation will still be demonstrated.

4. Can the Bernoulli bag experiment be used to explain other real-world phenomena?

Yes, the Bernoulli bag experiment can be used to explain many real-world phenomena, such as how airplanes are able to stay in the air and how curveballs in baseball can be thrown. It also has applications in industries such as aerodynamics and fluid mechanics.

5. Are there any safety precautions to keep in mind when conducting the Bernoulli bag experiment?

Yes, it is important to use a plastic bag and a small straw for this experiment to prevent any potential injuries. Additionally, ensure that the bag is not overfilled with air to avoid bursting. It is also recommended to conduct the experiment in a clear and open space to prevent any accidents or damage to nearby objects.

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