Principle Demonstrated: Bernoulli’s Law
PH.7 The student will investigate and understand properties of fluids.
… f) Bernoulli’s principle.
Conceptual approach to Bernoulli’s Principle.
Before turning on the leaf blower look in the direction the blower will be pointing. Don’t aim the leaf blower towards any loose posters on the wall or towards anything hanging from the ceiling.
When doing a demonstration I like to have the students do three steps as part of the demonstration.
Observe the demonstration. If possible I'll have the students be a part of the demonstration.
Now for this demo's details.
How the physics is demonstrated
Bernoulli’s principle says that air that is moving fast compared to the surrounding air creates a lower pressure. The air moving over the top of the toilet paper is moving faster than the air underneath the toilet paper. This creates a lower pressure above the toilet paper. The high pressure lifts the toilet paper up into the air steam of the leaf blower.
Construction and Tips Regarding the Demonstration
This presentation is quick, simple and gets more than one student involved. If you have the resources you can redesign a leaf blower just for the purpose of building a quicker "T.P.'ing machine". Get a point roller and slide a roll or 2 of toilet paper on it. Use duct tape, (Gorilla™ tape would be better,) To attach the roller to the end of the leaf blower's air tube. You may need some wood to prop it at the right height and to keep the roller level.
If the wind speed is 75 mph over the top of the tissue paper then how would a strip of 50 squares be lifted? Better yet, measure the air speed of your leaf blower and use this for this calculation.
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