Bernouli's Principle Botched

I found a fun science experiment book--just little activities that can be done easily to illustrate random scientific principles.  I thought it would be fun to use for Matters of Interest here and there.

Yesterday I was all set to illustrate Bernouli's Principle by using a hair dryer to blow air across the top of a roll of toilet paper that was loosely looped over a broom handle.  The air was supposed to cause the toilet paper to rise and blow forward and cause the roll to unroll.

It sounded fun!

It wasn't.

The air blowing across the toilet paper did nothing more than cause the loose end of the toilet paper to rise and flap in the breeze.  We tried higher air flow.  We tried lower air flow.  We tried nudging the roll a little to get it going.

Nothing worked.

I tried to salvage the moment by showing them how cool it was that the TP would at least lift with all that air on the top and describing how this principle works over airplane wings.  E12 said with attitude, "So if someone blew air across the top of my head, I'd float?"

"Yes!" I exclaimed.  "If the air could move fast enough or hard enough above you to counteract the effects of gravity, and we could get the air pressure underneath you started, then you'd float.  You're lighter than an airplane, and airplanes are held up by the air pressure underneath them."

"You mean the only thing holding up a plane is air?" yelped S9.


"I'm not going on any more plane rides!" she stated firmly.

E12 grinned and said, "Cool!  I'm going to try to fly!"

Perhaps the lesson wasn't so botched after all?


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