Date: Fri Sep 21 09:24:57 2007

Author: Richard Heckathorn

Subject: Exploding Can

Post:
Greetings,

I first saw this demonstrated at a "Man Made
World" workshop.

They were demonstrating that the explosion would
occur only with a correct air gas mixture.

I have a Charlie Chip can that I do the demo with.
I set it up, light the gas at the top and go on
with my teaching. In about 10 minutes it goes off
and any student who were asleep were no longer.

Seriously, I then tell the students that we have
much equipment that they do not know about that
might cause a problem if they do not know how to
operate it. So, please ask if you would like to
know how something works.

A charged van de Graaff generator connected to a
small Leyden jar setting on the counter will also
draw attention to inquisitive students who cannot
keep their hands off things.

A string (with do not pull) connected to something
overhead will always get pulled.

Maybe in a time of lawsuit happy people this needs
to be curtailed.

Dick




Helping teachers who facilitate, motivating
students who learn.
Dick Heckathorn 14665 Pawnee Trail Middleburg
Hts, OH 44130 440-826-0834
web.cvcaroyals.org/~rheckathorn/
Adjunct Physics Teacher - Baldwin Wallace College
Physics is learning how to communicate with ones
environment so that it will talk back.


-----Original Message-----
From: tap-l-owner@lists.ncsu.edu
[mailto:tap-l-owner@lists.ncsu.edu] On Behalf Of
Douglas Johnson
Sent: Thursday, September 20, 2007 2:54 PM
To: tap-l@lists.ncsu.edu
Subject: Re: [tap-l] flame tube safety question


I believe this demo is very safe since most of us
have one and have
never seen this as a threat for 10 or more years.
I also have a
explosion can demo, with a gallon size paint can
filled with natural
gas. The hole is 1/2" in diameter in the top of
it and a smaller
side hole on the bottom edge. When it is filled
with natural gas,
when the gas source is turned off, it takes 10
minutes after the
flame is on to explode off the lid of the can.
The air/fuel mixture
has to be just right before the explosion occurs.
As already
mentioned, the holes are small enough that the
flame will never get
into the tube and when the gas is turned off, the
flames go out at
the same time. The exploding can demo I described
is found on the
weblink below. ....Doug J.

http://parallax.sci.csupomona.edu/e107/showdemo.ph
p?demindex=TH-F-EG



>Daniel,
>
>I've not done this one. But I really want to.
>
>The one thing that bothers me about this design
is the possibility
>of a gas/air mixture inside the tube igniting. I
suppose that the
>energy of a small volume like this isn't very
much. But in a
>tightly-sealed rigid container I'm not sure I
know the maximum
>possible pressure. The temperature, pressure, and
combustion rate
>all feedback on each other.
>
>I'd be much more comfortable with this one if it
included a larger
>hole somewhere that was sealed with a thin piece
of tape. If it
>would happen to ignite, the pressure could blow
out this hole and
>would not build up. It seems like that would
greatly lower the
>maximum possible pressure.
>
>A little bit of failure testing with various gas
mixtures would be
>reassuring... and a lot of fun. Add a spark plug.
There might even
>be a new demo in that.
>
>Paul
>
>
>
>On Sep 19, 2007, at 3:46 PM, Daniel Kaplan wrote:
>
>>I am a high school physics teacher. My physics
club students want
>>to build a ruben's tube. I would like to use
this in my classes. I
>>want to build a version that will go on my
teacher demo desk which
>>is only 8 feet long. This is in a traditional
classroom that has
>>10' high ceilings. The demo desk is 3' from the
nearest wall. Since
>>there is house gas on the demo desk, I planned
on using that for
>>the gas source. From the videos that I saw on
line it seems like I
>>should be able to control things fairly well. If
I take reasonable
>>precautions, does anyone see any issues about
trying to make this
>>work under those constraints?
>>
>>
>>Thanks.
>>
>>
>>Daniel Kaplan
>>
>>Physics Teacher
>>
>>Matawan Regional High School
>>
>>NJ




From tap-l-owner@lists.ncsu.edu Fri Sep 21 09:24:57 2007
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