Date: Mon Apr 23 15:38:17 2007

Author: Frank Cascarano

Subject: Re: Big, loud, impressive demos

Post:
We do this several times a year. See my website for some pictures (just
keep hitting refresh for more photos): www.foothill.edu/~cascarano
We use a large PVC pipe with a bunch of tennis balls, which get launched
150-200 feet in the air. Very impressive. Not just the launch, with the
water and loud bang, but then waiting for the balls to come back down.
To answer your questions:
1) use a small weight (about 5 lbs)
2) We use a normal (32 gallon) plastic trash can, filled completely to the
top with water. We have a 5 foot length of 8" diameter PVC pipe (open at
both ends) sitting vertically in the trash can. Drop in the weight and
bottle, add about 15 tennis balls, and get back. I have no idea where to
get the PVC pipe. It was donated by a student who works on construction.
3) About an inch in the bottom of the PET bottle. Use bottles that are
made to hold pressure (carbonated soda bottles, about 1 liter work
well). Water bottles don't seem to work.
4) It is always a big hit for us.

Feel free to email me if you have any more questions. (Finally, I get to
contribute to the list!)
-Frank

At 07:15 AM 4/23/2007, you wrote:
>Hi all,
>
>Our Chemistry department put on an impromptu outdoor demo show last year
>that included a host of impressive demos: The thermite reaction, igniting
>a hydrogen balloon, natural gas soap bubbles, sodium in water, among others.
>This year, I'd like to counter their demos with a series of my own. I
>have questions about a specific one I saw a few years ago, but please feel
>free to add suggestions to this thread.
>
>At a Summer AAPT meeting in years past (Sacramento, I'm thinking), I
>witnessed the following demonstration.
>
>A weighted 2-liter bottle was partially filled with liquid nitrogen and
>then sunk to the bottom of a barrel full of water. A few seconds went by
>and BOOM - a large volume of water was displaced in approximately three
>nanoseconds. There was an audible gasp from the audience. I've been
>talking about this demo ever since I saw it, but since we don't typically
>do large demos shows at Haverford, I've never tried it myself. I have a
>few questions about the safety of this demo, before I blindly test it out.
>
>1. By what mechanism was the bottle sunk in the barrel? I want to ensure
>I design something that doesn't become a projectile.
>2. Is it safe to do this demo in an industrial sized plastic barrel (i.e.
>a large cylindrical trash bin) or should I use a metal drum. If it's the
>latter, does anyone know where I can acquire one?
>3. How much LN2 should I use?
>4. Is this demo as surprising as I remember?
>
>Other ideas for spectacular outdoor demos would also be appreciated!
>
>Thanks very much,
>Scott Shelley.



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