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Alka-Seltzer Rockets

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m85476585

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The rocketry club at Georgia Tech is going to do a demo for elementary school students, but we are not allowed to launch rockets on campus. We can fly alka-seltzer rockets, but I don't know where to find Fujifilm canisters for them. I will check all the drug stores and camera places around here tomorrow, but it has been years since I've used film for anything, and I don't think I will have much luck finding any film canisters that will work (Kodak ones will not since the lid is not tight enough). Does anyone know where I can find film cans or a similar container that will work?
 

DaveCombs

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That really is the best place to find them - anyplace that does 1-hour or next-day processing. I grabbed a bunch from one of our local WalMarts, but they have since parted ways with me (I think we used most of them in a Scout welcome night to make little medical kits for the kids).
 

Gillard

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i've used alka seltzer and camera film cases lots for teaching acid reactions and rates of reactions.
i went to a local film developing place and they gave me a bag with about 300 cases. that was 4 years ago and i still have not used them all.
- try baking soda, its cheaper.
 

Micromeister

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They are a trip!
Yep any of the one hour shops or drug stores with photo printing. I also have friends and family Saving Fuijfilm canisters whenever they buy film.
1/8" craftfoam makes wonderful fins and NC.
 

proflaser

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An alternative for the selzer rockets is an air stomp rocket. It's a little effort to make a launcher out of a soda bottle and some tubing, but the rockets are safe.
 

m85476585

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An alternative for the selzer rockets is an air stomp rocket. It's a little effort to make a launcher out of a soda bottle and some tubing, but the rockets are safe.
How would you build the stomp mechanism?
 

Micromeister

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Can someone post a link to plans? Please?
Believe it or not, I can't put my hands on the photos I took at one of your launches last fall were I was pushing these alki-Rocs as part of a youth outreach program.
I'll have to see if I just deleted them or have them on a different flash drive.
I'll take a couple more pics of the parts and patterns. I know I didn't bother with a drawing I just happened do see that fuij Flim canisters fit very neatly in some of my old pile bottles and went on from there.
We used to do this with Baking soda and vinegar in school in the stone age 60's. shooting the film canister top accross the room, or a cork tapped in a large test tube. same reaction. The Alka-Seltzer rocket just inverts the process launching the bottle bottom rather then the lid:)
By using Alka Seltzer tables or a half table as the case may be, we can eliminate the vinegar (acid) substituting water instead sill generating enough CO2 to launch the bottle (model body). by adding the pill bottle to the mix it gives a little more body to the overall toy. and allows adding fins and other such to make it look a little more like something other then an empty film canister.
OH! one more observations these things need as hard (solid) and stable a surface as possible to launch from. a concrete curb is great. you can get 30-40 feet from a halftab flight. on a softer soil or plastic container top far less. Action and reaction remember.

Matt:
Making a stomp rocket ball launcher isn't that much trouble either; a good sized soft rubber ball, small pices of PVC pipe and some flexable hose that fits the PVC, and some duct tape are about all you need. Add a few old models(with taped or glued on nosecones) and an piece of tube to fit inside and away ya go:)
 
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Micromeister

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Couldn't find the flight pics, they must have gotten trashed:(

Heres a couple construction pics that may help. Give em a try that are truely a blast:)

Alka Seltzer-a-sm_(CO2) Rocket Parts & Pieces_06-2008.jpg


Alka Seltzer-b-sm_(CO2) Rkt Body Pill bottle& fuji can_08.jpg


Alka Seltzer-c-sm_(CO2) rkt 8th inCraftfoam fins_07-04-08.jpg


Alka Seltzer-d-sm_(CO2) Rkts & fuji film Canister_07-04-08.jpg
 
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RocketT.Coyote

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The current CAP Model Rocketry Program has participants building rubber-band-powered Goddard Rockets. These are made of foam pipe insulation, meat tray fins hot-glued in place, Rubber-band looped onto a soda straw and secured to the nose with a nylon tie-wrap. These are followed by Fuji-cannister rockects before going on to solid-fuel models. Sounds almost like 4-H Club's program.
 
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mjennings

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I don't know if there are any stores like this near Georgia Tech but back home in St Louis there are a couple of "electronic" stores that sell refurbished parts and such. They tend also to have lots of odds and ends, like film cans, pill bottles, and such. Also there are "Recycle Shops" that take the "One man's trash is another man's treasure" principal and applies capitalism to it. They sell peanut butter jars, egg crates TP tubes etc, for a small price, ie all you can fit in a paper grocery bag for $5. Might work out for you if you can find one of these.

Also you might want to try a specialty camera shop that does developing.
 

MarkII

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I'm not sure why the firmness of the surface that they are launched from should make any difference -- if these are reaction motors, then they shouldn't need anything outside of the rocket for the exhaust to push against.

MarkII
 

Micromeister

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Makes a HUGE difference in preformance. The harder the surface the canister cap is sitting on decreases the mount of deflection of the pressure released.

Observed examples:
* 1st flt: model set directly on a concrete curb sent the model about 35-40 feet.
* 2nd flt: Same model sitting on a rubbermaid 30gal tub soft Plasitc top set on grass sent the model about 7 feet.
*3rd flt: same day, same model set on dry dirt sent the model about 12-15 feet.
*4th flt: same model on another concrete curb, flight to about 30-35feet.
While it's true some portion of the difference comes from the amount of gas generated during build up in the model reaction of the tablet half in water, it doesn't account for that much difference, especially when the first and second flight examples were from the same tablet, which was split pretty closely in half with the same measured amount of water. This does assumes the "pop" pressure between cap and body remains about the same over these three flight, but will, i'm sure degrade with ware over time.
 
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MarkII

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So, hypothetically, such a rocket would not produce any thrust if it was operated in the vacuum of space, because its exhaust jet would have no surface to push off against after it left the nozzle? I must have misread Newton, then. I always thought that the amount of thrust that a reaction engine generated was (at the scale that we use them) determined by the amount of mass ejected out of its nozzle and the speed at which it was ejected. I did not think that the thrust of the engine itself was affected at all by whether or not there was a hard, solid surface for the exhausted mass to strike after it left the engine.

MarkII
 

Peartree

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Of course not. I'm thinking that a softer surface allows more mass (the lid) to be thrown away quickly. Perhaps on a hard surface the lid come off more slowly (in relative terms) thus creating a more beneficial thrust 'nozzle' around the edge of the lid?? It's got to be in the physics somehow.
 

Micromeister

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Of Coarse not; we have no nozzle as such.

Actually without going onto all the useless details... These seltzer rockets are more like a rifle shot with recoil then Rocket engine firing....who CARES which of Newtons laws are being followed.. and they are.... these little things are so much fun, the kids really don't need to know the difference at this level.
Just take the experience for what it is, EXPERENCE and follow the advice or better yet stop talking about stuff that really doesn't make any difference and go do some experimenting on your own and have some fun:)
 
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falingtrea

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Looks like those would also work with solid CO2(dry ice) as well. I used to make them at work using the photo coating containers that came with polaroid BW film we used in a scope camera. Great way to make a co-worker jump when they went off. :D
 

MarkII

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So they work more like tiny mortar shells or cannons? That would explain why the escaping gas needs a hard surface to rebound against. In any event, they sound like a hoot. :D

MarkII
 

falingtrea

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Yeah, A soft surface would act like a recoil pad on a gun and absorb some of the energy that would have been used to propell the "rocket"
 

RangerStl

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Of course not. I'm thinking that a softer surface allows more mass (the lid) to be thrown away quickly. Perhaps on a hard surface the lid come off more slowly (in relative terms) thus creating a more beneficial thrust 'nozzle' around the edge of the lid?? It's got to be in the physics somehow.
The more a lid moves, the more energy it absorbs and takes away from the forward flight of the can. If you set it on a curb, the reaction is trying to move the earth backwards. Mass of earth is nearly infinite w.r.t. can so velocity of earth ~ 0. Thus the momentum extracted from the system nearly zero.

If you set it on a plastic tub, you move the plastic tub and the momentum of the lid's movement is subtracted from the can's forward flight.

Not thrust, just momentum conservation.

N
 

Peartree

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I might have thought so, but wouldn't the the mass energy equation only include the mass of the lid and its speed? The energy imparted on the "rocket" would be equal to the force with which the lid was thrown. Once the distance of the lid to the "rocket" is greater than zero, it cannot impart force upon it directly but has to act in some indirect fashion.

Example: If an astronaut throws a baseball, he/she is pushed back with a force equal to the force imparted on the baseball. Once the ball is released, regardless of what the ball hits, there is no additional effect on the astronaut.
 

MarkII

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I might have thought so, but wouldn't the the mass energy equation only include the mass of the lid and its speed? The energy imparted on the "rocket" would be equal to the force with which the lid was thrown. Once the distance of the lid to the "rocket" is greater than zero, it cannot impart force upon it directly but has to act in some indirect fashion.

Example: If an astronaut throws a baseball, he/she is pushed back with a force equal to the force imparted on the baseball. Once the ball is released, regardless of what the ball hits, there is no additional effect on the astronaut.
I was wondering that, too. This was the heart of my original question (much less clearly expressed than yours). If having a hard rebound surface behind it really makes that much difference in the resulting trajectory, then the "rocket" is really being propelled more in the manner of a mortar or artillery shell. Which means that it is not really flying as a result of rocket propulsion at all, but by an explosive discharge. ("Explosive" meaning, in this case, the sudden release of a pressurized gas.) Although the "Alka-Seltzer rocket" is not being blasted out of a tube, the firm launch surface that seems to be so necessary for its performance is acting just like the rear bulkhead of a mortar tube or howitzer. In true rocket propulsion, it is the movement of the reaction mass out of the nozzle, and not what the mass strikes afterward, that produces the thrust.

MarkII
 
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Micromeister

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I believe this was sort of stated in post 18. Rifle, mortar, or Cannon all the same reaction. They are not "really" rocket propelled, again we have no nozzle involved.
 

Peartree

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I was wondering that, too. This was the heart of my original question (much less clearly expressed than yours). If having a hard rebound surface behind it really makes that much difference in the resulting trajectory, then the "rocket" is really being propelled more in the manner of a mortar or artillery shell. Which means that it is not really flying as a result of rocket propulsion at all, but by an explosive discharge. ("Explosive" meaning, in this case, the sudden release of a pressurized gas.) Although the "Alka-Seltzer rocket" is not being blasted out of a tube, the firm launch surface that seems to be so necessary for its performance is acting just like the rear bulkhead of a mortar tube or howitzer. In true rocket propulsion, it is the movement of the reaction mass out of the nozzle, and not what the mass strikes afterward, that produces the thrust.

MarkII

Micromeister said:
I believe this was sort of stated in post 18. Rifle, mortar, or Cannon all the same reaction. They are not "really" rocket propelled, again we have no nozzle involved.
I typed a post about this yesterday morning but before I could finish one of our cats sat on the mouse and deleted it (at least I think that's what happened) and then I had to leave for work so I couldn't finish. Whether there is a nozzle or not doesn't answer the question we've been ruminating (don't get to use THAT word very often) about. In a pure action/reaction event whether there is an explosion or a nozzle controlled impulse, we're not clear on why the "launch" surface has a significant impact on the altitude attained. I knew he answer had to be in the physics and I think that you are both right. If it were a nozzle controlled impulse, the force of the jet from the nozzle pushes against the air/atmosphere and so the surface wouldn't matter, but why does the surface matter? An explosion action/reaction *should* be like the astronaut/baseball example. The explosion just pushes the lid away transferring the force of the transferred energy to the *rocket.* Since Micromeister's experiments clearly show that the surface matters, it is obviously not quite so simple.

What I think is happening:

It *is* like (or at least similar to) the astronaut/baseball example but with an important difference. In this case, the astronaut is standing next to a brick wall. If he is sufficiently close to the wall, then when he "throws" the ball (the explosion) the ball goes nowhere (and is not a part of the mathematics/physics problem at all) but the astronaut "pushes off" against the wall. All of the energy of the "push" is transferred to the astronaut/rocket since the wall obviously isn't going anywhere.

If the astronaut is a step (maybe a half step) away from the wall and throws the ball, the energy is transferred differently. Instead of pushing off against the wall and *all* of the energy being transferred to the astronaut, some of the energy is transferred to the astronaut/rocket and some to the baseball/lid. Given a fixed impulse, conservation of energy demands that the more things that are made to move from the force of the explosion/push, the less energy each of them can have.

If this is what is happening, then in order to maximize the altitude of the "rocket," one would want to design your base so that the film can lid does not move at all (or as little as possible).

Does that sound right?
 

Micromeister

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I typed a post about this yesterday morning but before I could finish one of our cats sat on the mouse and deleted it (at least I think that's what happened) and then I had to leave for work so I couldn't finish. Whether there is a nozzle or not doesn't answer the question we've been ruminating (don't get to use THAT word very often) about. In a pure action/reaction event whether there is an explosion or a nozzle controlled impulse, we're not clear on why the "launch" surface has a significant impact on the altitude attained. I knew he answer had to be in the physics and I think that you are both right. If it were a nozzle controlled impulse, the force of the jet from the nozzle pushes against the air/atmosphere and so the surface wouldn't matter, but why does the surface matter? An explosion action/reaction *should* be like the astronaut/baseball example. The explosion just pushes the lid away transferring the force of the transferred energy to the *rocket.* Since Micromeister's experiments clearly show that the surface matters, it is obviously not quite so simple.

What I think is happening:

It *is* like (or at least similar to) the astronaut/baseball example but with an important difference. In this case, the astronaut is standing next to a brick wall. If he is sufficiently close to the wall, then when he "throws" the ball (the explosion) the ball goes nowhere (and is not a part of the mathematics/physics problem at all) but the astronaut "pushes off" against the wall. All of the energy of the "push" is transferred to the astronaut/rocket since the wall obviously isn't going anywhere.

If the astronaut is a step (maybe a half step) away from the wall and throws the ball, the energy is transferred differently. Instead of pushing off against the wall and *all* of the energy being transferred to the astronaut, some of the energy is transferred to the astronaut/rocket and some to the baseball/lid. Given a fixed impulse, conservation of energy demands that the more things that are made to move from the force of the explosion/push, the less energy each of them can have.

If this is what is happening, then in order to maximize the altitude of the "rocket," one would want to design your base so that the film can lid does not move at all (or as little as possible).

Does that sound right?
John:
If your using the "ball" as the film canister lid, than yes what your thinking is pretty close.
If we use that same astronaut, ball and make the wall a streatched rubber surface in an anchored frame you'll see that some of the "Push" is absorbed or countered as he pushes off the surface which "gives" in proportion to the Push exerted. Personally I think the Rifle or Cannon recoil explaination is a closer example. The softer the retaining surface or entitiy restraining the solid surface (lid) the more energy is transferred away from the projectiles push.
Add the softness (flexability) of the grass under the semi-soft plastic tub top greatly increases the amount of distance the retaining force can travel transferring even more of the energy from the push.
 
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falingtrea

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What would probably be a better example would be to take that baseball and try to bounce it off of two surfaces, grass and cement sidewalk. On which surface does the ball bouce higher, if at all??

Another thing to try. What would happen if you put the "rocket" on a rubber membrane? I bet the cap would fly higher than the rocket body.
 

MarkII

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In a mortar tube, a cannon or a rifle barrel, and explosion is set off between the projectile and a solid bulkhead at one end of a tube. The explosion is not strong enough to burst the bulkhead or blow through the side of the tube, so it takes the path of least resistance and pushes the projectile out of the way (with considerable force) during its process of expansion out of the opening at the other end of the tube. The gas is contained, with only one exit, and this is what is harnessed to move the projectile.

The Alka-Seltzer rocket is not launched from a tube (imagine how high it would go if it was!) but it tossed into the air through an identical process. Imagine if you took a cannon (on a movable platform), loaded it and placed its mouth right up against the side of a cliff. When you fired it (by remote control from a safe distance), the cannonball would be forced down the tube toward the mouth, but would be stopped by the cliff face. The gas created by the explosive charge will still be expanding and seeking an outlet, and since it cannot move the ball (or the cliff), it will move the cannon.

In the Alka-Seltzer rocket, the cap is the cannonball, the canister itself is the cannon, and the firm launch platform is the cliff face. Yes, there is a large conservation of motion effect, since because the launch platform doesn't move, all of the energy is applied to the canister once the cap is blown off. But another important factor is that the firm launch surface, by stopping the cap (cannonball) before it completely separates from the canister, causes the expanding CO2 (the explosive charge) to be contained long enough to effect a large and powerful movement of the cannon (or canister).

This is somewhat similar, but not identical, to the way a rocket engine propels a rocket. In a rocket, as in a cannon, gas is rapidly generated by the burning of a highly energetic propellant within a closed-end tube that has only one outlet. In a rocket, though, the propellant undergoes a controlled burn, rather than explodes, and it passes out of the only opening in the tube through a nozzle that accelerates it to supersonic speed. The rocket moves by jet propulsion, and is not simply thrown aloft by an explosive charge. (An important distinction that seems to have been lost on a certain government agency.) So the Alka-Selter projectile (not really a rocket) is shot up into the air in the same way that a cannon shoots a cannonball, not in the same way that the Space Shuttle lifts off from the KSC.

MarkII
 
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