Date: Thu, 28 Aug 2003 17:45:37 -0400

Author: John Cockman

Subject: Sodium Polyacrylate


Apparently Texas law does prohibit anything like this:

zip gun: a device or combination of devices that was not originally a
firearm and is adapted to expel a projectile through a smooth-bore or
rifled-bore barrel by using the energy generated by an explosion or
burning substance.

Here's a case in Colorado:


On Thursday, August 28, 2003, at 12:18 PM, Karl Trappe wrote:

> I doubt that they are illegal because I doubt that the issue has ever
> been raised by anyone in authority to outlaw them. The potato guns
> were outlawed in some communities where they were misused. Its a
> little harder to over-project the tennis ball.
> I agree that cardboard seems safer, but I do believe that multiple
> tape seams are much weaker than most cardboard, so it would fail
> before the cardboard. I'm not sure how you would create the gas
> expansion chamber in a cardboard one, or how you would plug the end
> piece of that chamber, from which all of the gas must "react" to
> propel the ball forward.
> If you still want to build one...those are the instructions I used.
> Karl
>> I've never built one.
>> But I must advocate making these out of cardboard. It's plenty
>> strong enough. It's used to send fireworks hundreds of feet into the
>> air by the same method.
>> When cardboard ruptures, the shards have a very low density and do
>> not have a long range in the air. A metal shard can go a long
>> distance and still put holes through you when it gets there.
>> The duct tape may be a reasonable precaution. But the steel can
>> cannon looks a lot like a pipe bomb.
>> I read somewhere that these devices are actually considered to be
>> "zip guns" and are quite illegal.
>> Paul
>> On Wednesday, August 27, 2003, at 11:10 PM, Karl Trappe wrote:
>>> Bob: This is Andy Graham's formula from Appalacian State.
>>> You *MUST* assemble this canon with duct tape (carpet tape). This
>>> is for safety reasons. If a joint fails due to excess gas
>>> pressure...that's good, because the alternative is for the can to
>>> fail and send fragments outward. With that said, the cans are the
>>> next item.
>>> Used to be, you used soup cans, because they were exactly the right
>>> size to stuff a tennis ball snugly enough to get sealing of the
>>> chamber for the gas pressure to build up. Now, you will have to
>>> locate the diced tomato cans that are the same size. Be sure to
>>> compare them in the store before buying. The reason is that nearly
>>> all soup cans have a seamless bottom. You need cans for which you
>>> can 'can open" the top, and in some cases the bottom, as well. You
>>> *could* use a mixture of cans.
>>> The 1st can is the ignition chamber. It could be a seamless can.
>>> Remove the top completely. Drill a hole in the side near the bottom
>>> end. This will be the lighting hole. Something in the 1/4 to 3/8
>>> inch diameter should work well.
>>> The 2nd can has a large hole cut in the bottom, to which a tennis
>>> ball nicely plugs the opening. I use a chassis punch, gut you could
>>> use a circle saw to cut this clean and symmetrically round hole.
>>> Remove the top completely.
>>> The 3rd and 4th (and possibly 5th) cans are just barrel extensions.
>>> They must be cans for which you can remove both ends.
>>> Now assemble your barrel with duct tape wraps at each seam. Two
>>> windings overlapping should be enough.
>>> Now tape your barrel to your wheel set. We use a roller skate base.
>>> Make certain that the ignition hole is pointing upward.
>>> Fueling is the next trick. Sometimes we use conventional lighter
>>> fluid. You could use methanol in a squirt bottle. The amount is
>>> tricky. *One* nice squirt should do. Squirt it into the lighter >
>>> hole.
>>> The next step is critical. Rotate (swirl) the canon so that the
>>> entire surface of the 1st can is coated. Often, we "sling' the
>>> excess out the barrel to get rid of *liquid* fuel. Remember, its
>>> the vapor that fires this thing, not the fuel burning.
>>> HOWEVER* too much fuel vapor without enough oxygen, will result in
>>> the canon being a dud. This is the most annoying part of this demo.
>>> In fact, 2nd firings usually fail because of too much unspent fuel
>>> or too much burned fuel and insufficient oxygen to allow a burn.
>>> *Subsequent firings* almost always require blowing out the chamber
>>> to replenish the oxygen.
>>> Next insert the tennis ball into the end of the barrel. Poke it to
>>> the back of the barrel until it seats on the hole at the bottom of
>>> the 2nd can. This will close off the 1st can as the single burn
>>> chamber. If you inserted the tennis ball before fueling, you can
>>> expect to burn the fuzz off of the tennis ball in a nice circle the
>>> size of the 2nd chamber bottom. It does not smell good.
>>> Lighting is straightforward. Use one of those fireplace lighters
>>> (or even a fireplace match). But watch where you point the thing.
>>> This *is* a canon, after all.
>>> The lighter the wheel set the better the recoil, but suit yourself
>>> depending on what you want to show. If you place this demo on a
>>> tabletop, be sure to block the wheels in the recoil direction or you
>>> will have a dented and inoperable canon. At some point you'll grow
>>> tired of eating diced tomatoes...
>>> Enjoy, and thanks to Andy Graham for many years of doing this one at
>>> the AAPT Lecture Demo Workshops. Karl
>>>> Does anybody have some simple plans for a tennisball cannon using
>>>> lighter fluid? I have a toy truck to attach a cannon to, but I'm
>>>> not
>>>> sure what to use for thr cannon part.
>>>> Thanks,
>>>> Bob Torrelli
>>>> Euclid High School
>>> --
>>> Dr. Karl I. Trappe Desk (512) 471-4152/471-1823
>>> Lecture Demonstration Office Office (512) 471-5411
>>> Physics Department, Mail Stop C-1600 Home (512) 264-1616
>>> The University of Texas at Austin
>>> Austin, Texas 78712-1081
> --
> Dr. Karl I. Trappe Desk (512) 471-4152/471-1823
> Lecture Demonstration Office Office (512) 471-5411
> Physics Department, Mail Stop C-1600 Home (512) 264-1616
> The University of Texas at Austin
> Austin, Texas 78712-1081
From Thu Aug 28 18:10:58 2003
Date: Thu, 28 Aug 2003 17:45:37 -0400
From: John Cockman
Subject: Sodium Polyacrylate
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I found a supplier for Sodium Polyacrylate (the super absorber in disposable

Carolina Biological Supply Company

The catalog number is 89-1480.

Is there a PIRA number for this demonstration?

John Cockman

From Fri Aug 29 00:07:53 2003
Date: Thu, 28 Aug 2003 21:10:25 -0700
Subject: Re: Sodium Polyacrylate
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