Presenter: Tony Wayne, Albemarle High School, twayne@k12albemarle.org.     

Va. SOL:
PH.7   The student will investigate and understand properties of fluids.
            … f) Bernoulli’s principle.

National Standards:
http://www.nap.edu/readingroom/books/nses/html/6e.html#ps

Topic/Concept
Conceptual approach to Bernoulli’s Principle.

Materials

• Bernoulli shooter (see construction details below.)
• 3 or more Ping Pong™ balls
• leaf blower

Safety Considerations

            Don’t aim the shooter towards any students.

Presentation

This makes a good culminating activity for Bernoulli’s principle.  Have a student hold the leaf blower in such a way that it blows horizontally. Take 3 or 4 ping pong™ balls and load them into the vertical tube. Then hold the shooter such that the air flows through the horizontal tube. The ping pong balls will shoot out of the horizontal tube in a few seconds. Then I show an animation showing how it works. Here is the animation.

How the physics is demonstrated

This video is located on YouTube at http://youtu.be/1L9ymG2wyyY

Bernoulli’s principle says that air that is moving fast compared to the surrounding air creates a lower pressure. The air moving horizontally through the tube is faster than the air in the vertical tube. This means a lower pressure is created above the vertical tube causing the higher pressure under the tube to move the balls up into the air stream.

In the video shown above. the balls bounce as they are pushed up into the air stream. Also, this shooter has 1/2 inch holes drilled into the vertical feed pipe. These holes are covered up with clear packaging tape. The purpose of the holes is to see the balls rise. Although it happens so fast that is was only seen at 240 frames per second.

Construction  and Tips Regarding the Demonstration

This is made from 1.5” SCHEDULE 40 PVC pipe. This will pipe will fit a ping pong™ ball perfectly with about 1 mm of room to spare. The pipe is available from a hardware store. Take a ping pong™ with you to check for size compatibility. You will need a section about a foot long and a second piece about 18 inches long. (You may need a pipe cutter or a hack saw to cut these pieces out of a 5 or 10 foot section that the store sells.) The lengths are not critical. You will also need a “Tee” section. This will connect the two sections. Stick them together in a 90° configuration. You can use PVC cement to permanently hold them together. (If you do use the PVC cement pay special attention to the warnings. The fumes are very dangerous. I only use it outside.) A friction fit without the cement is enough to hold the pipe pieces together.

Extension

Have the students calculate the minimum air needed to accelerate 1 ping pong ball at 1.00 m/s².

Sources & References

None