Thursday, August 28, 2008

Menticulation of Diet Coke in Microgravity!

Note: since the appearance of the slashdot story, lots of people are commenting and making suggestions.  Thanks!  I'll reply to them as a group in a day or so.

As I've mention in several prior postings in the blog, the big experiment we wanted to do during the flight was seeing how the Diet Coke & Mentos reaction works in microgravity. If you haven't read those posts, please do so to get an idea of how the experimental apparatus and goals evolved over several weeks. You may also want to check out my Youtube videos for other high-speed videos I've done, including one that shows the reaction at 1200fps on the ground.

Before I go any further, I want to thank everyone at ZeroG and Space Adventures that went the extra mile to make this experiment possible, in particular the science liason, Michelle Peters. And I'd also like to thank the TSA screeners, who arrived on site already totally up to speed on what we wanted to do (they'd even seen my test videos). Whatever you may think about the rules that the TSA enforces (and I agree with Bruce Schneier in that regard), the fact of the matter is that the frontline staff that you deal with have little or no freedom to apply common-sense discretion, and are often placed in situations where they don't have the time, or the background knowledge, to make an informed decision, which means that the default answer is "no". When you couple that with the fact that anyone can be having a horrible day, and some small percentage of people are jerks to begin with (a smaller percentage than most people assume), and multiply by hundreds of thousands of people going through security a day, it's a recipe for horror stories.

But in our case, since the screeners had been pre-briefed, it was easy to demonstrate that everything we wanted to use was well within the TSA rules. The only thing that didn't fly was a tiny ball of modelling clay that we were going to use to mount the mento onto a ziptie with, and the screeners helped brainstorm an acceptable (and better!) mounting method.

As described in a previous post, the hypothesis that we wanted to test was that convection of the soda was an important part of the whole reaction; under normal gravity, bubbles formed around the mentos rise up through the soda, allowing more soda to come in contact with the candy, and thus more bubbles form. However, in microgravity, there's no "up", so any bubbles that form will just stay near the mento, and will in fact keep new cola from reaching it.

So lets get right to the video, and then discuss what we learned.



I'll begin by discussing what went wrong.

Our first problem was that we weren't quite in free-fall, because in order to do the experiment, we had to be strapped into seats next to the emergency exit window (to get the light we needed). If you think about the geometry of the parabolic arcs from the perspective of the actual plane, the true zero-g path forms a parabolic plane, and (I'll try and state this as plainly as possible) the pilot attempts to fly a path that causes the (physical) plane to follow the (geometric) plane.

I say "attempts", because it's humanly impossible for a pilot to do this perfectly. So anything attached to the plane (as we were) is going to experience some small amount of residual gravity, not to mention the effects of any air turbulence.

Even if the pilot does this perfectly, only those parts of the (physical) plane that intersect the (geometric) plane will be in true free fall. Anything above or below that perfect plane (in the perfectly-flown plane!) will experience a slight amount of residual acceleration, because it's not free to orbit the earth in a free fall path, but is rather being dragged along either slightly faster or slower than it really wants to travel. In practice, of course, this tidal effect is tiny compared to the errors caused by the pilot as he or she attempts to fly the true parabolic path.

So because the experiment was attached to us, and we were strapped into the seats, and the seats were attached to the plane, the entire apparatus was subject to some residual accelerations. In order to eliminate them, the Mark II Menticulation apparatus will have to be free-floating, self-contained, and will have to operate without being touched. This will permit it to freely fall in a zero-g parabola independent of the path of the body of the plane (although there will be some residual effects due to things like air currents in the cabin, of course).

As a side-point, it's interesting to note that on these flights, from the standpoint of the passengers, the pilot doesn't need to fly an absolutely perfect parabola; as long as he or she can fly a path that is, on average, close to the perfect path, nobody inside the plane will really notice the difference.

The second problem we had was that we wanted to create a reasonably sized ball of soda, and then put the mento into it. However, the nozzle we used to control the soda flow was too small, and we couldn't control the exit velocity properly (and so we got all the squirts). On the second parabola (not in the video), we tried removing the nozzle, but we couldn't get a bubble of soda to detach from the bottle, and everything got messy - a blob of soda impacted right on the camera window, obscuring a lot of the view.

In order to fix this, we're going to have to come up with a method that deploys a preformed, properly positioned bubble of soda.

Finally, the video was slightly out of focus. We had to manually set the focus on the camera before doing the experiment, and it was difficult to keep the coke and mento at the correct distance, considering all the other things we were having to do.

Even with all these problems, I think we got some interesting video and results. It's not definitive, but it looks like the reaction is slowed down by the lack of gravity, and we also noticed something we weren't looking for; the cola apparently clings to the mento (likely, it's hydrophilic), resulting in the interesting dynamics when I moved the candy. A followup experiment might be to compare the behavior of some water surrounding a mento vs. a ball bearing.

The Mark II Menticulator - Initial Design

I've spent a few hours thinking about an improved experimental apparatus, and I think I've come up with something that, with a little refinement, will do the trick.

The experiment will be housed in a transparent case constructed of acrylic or lexan panels locked together by t-slotted structural framing. Inside will be a rubber balloon of soda trapped between two spoonlike holders, one above, and one below. A hobby r/c servo will be mounted inside the box, with two arms extending from it, such that if it rotates in one direction, a sharp tip will puncture the balloon, hopefully releasing the soda which will remain between the spoons; then when it rotates in the other direction, a mento will be moved to the center of the bubble of soda.

The servo will be directly controlled (no radios onboard!) by a small hobby microprocessor such as an Arduino. The microprocessor could also have some sensors to collect related telemetry (accelerometers and so forth).

Finally, several strips of high-intensity LEDs will provide the needed light for the Exilim EX-F1 camera.

46 comments:

Frank said...

Cool project!
I did an experiment in zero g with glass marbles a year ago.

http://raumwiese.macbay.de/zero-g/PROJECT.html

MadOverlord said...

Wonderful images, thanks for linking to them. Looks like you encountered similar issues with getting close to zero g in the camera field as I did.

Anonymous said...

I was struck by the thought that perhaps if a Mentos surrounded a steel ball bearing then perhaps it could be held in space by a magnetic field or even shot to an appropriate point in the experimental apparatus.

Nice vid
-Monsignor Funkibut

MadOverlord said...

That's possible, but there are several problems:

1) It would require significant magnetic fields and precision control over them. The pilot might get a wee bit upset when you fire them up and his backup magnetic compass goes berserk.

2) You couldn't test it under normal gravity conditions. You only get one shot per flight to get things right, so you want to control things as much as possible. The KISS principle rules here.

Anonymous said...

Cool experiment.

What song is that in the video?

MadOverlord said...

It's Aquarium, from The Carnival of the Animals, by Camille Saint-Saƫns.

http://en.wikipedia.org/wiki/The_Carnival_of_the_Animals

James Cape said...

Obviously, the balloon (or whatever) container you're using to keep the cola in has to be large enough so the balloon isn't being stretched when it's filled with cola.

Otherwise the balloon will be trying to push the cola out all the time, and when you puncture it the cola will come squirting out of the hole. [Insert $0.50 terms like "isobaric process" and "tensile strength" for all that here.]

Perhaps a hard container coated in such a way that the cola doesn't come with it when you crack it open? ["surface tension", etc.]

C. Watford said...

Glad to see a fellow Wilmingtonian getting some press on Slashdot. An alternate idea to the balloon is a plastic globe with a seam at the hemisphere. Motors could pull the two hemispheres apart revealing a (mostly) spheroid soda ball. Adding the mento would probably be best done on an arm you control, as I'm certain the soda ball's exact location will be highly variable. Regardless, have fun doing the next experiment!

Anonymous said...

Create a spherical container for the cola, and make it easy to remove the container from around the cola when in freefall. That might be a lot easier way to get a large sphere of free floating cola than to push it through any nozzle.

Mike said...

To create a large bubble of cola, you could try filling a baloon with the cola on the ground and sealing it. Escaping CO2 should pressurise it, then in microgravity you pop the balloon. Could get messy, but you hope the surface tension holds enough liquid together to be useful?

Anonymous said...

Very cool stuff. You might want to clarify some of the description: what you were experiencing was not residual gravity, but residual acceleration from the airframe not flying a perfect parabola.

Anonymous said...

why didn't you just drop a mento inside a cola bottle?

Anonymous said...

It seems like the easiest way to do this would be to use a baggie of of coke with an appendix baggie that holds the mento that is seperated off by a zip loc or other seal.

Ram said...

if you want a precise way of measuring the the rate of reaction, moreso than just eyeballing the bubbles you should try to measure the amount of gas evolved. If you took an empty (of air) plastic bag and sealed over the edge of the coke bottle, then removed it after a fix amount of time you could measure gas evolved. You would need to make an air/liquid tight seal between the bag and coke bottle. You could do the same experiment on earth and measure the volume there too. Seems like that would be cleaner and more precise than eyeballing an uncontrolled volume of soda reacting with a mentos. It would be hard to compare anyway.

Idea for measuring the volume: submerge the sealed bag in a measuring container full of water.

Aaron said...

hmm, would the balloon bursting cause a very large disturbance to the sphere? Maybe a test could be performed in something that's immiscible with the cola? Mineral oil is a little heavy, but could do the trick.

Or, stretch a balloon over a small drinking glass (shot-glass sized). Then the effects of the balloon on the soda would be minimized.

CPerdue said...

Rapid deployment setup: Impale 4 Mentos on a hollow metal 1/8'' rod, which is fed through a soda cap. Wrap the Mentos within a small, deflated balloon. Using tape, seal the end of the balloon onto the metal rod so it's airtight. Insert the tip of the rod with Mentos/balloon into an empty 2-liter bottle. Once in the 2-liter, blow on the metal rod to inflate the balloon around the Mentos. Once at desired size, seal the end of the rod so the balloon remains inflated around the Mentos. Insert a second metal rod through the soda cap, taping it next to the original metal rod, but positioning its tip about a 1/4" from the surface of the balloon. Sharpen the end of a thin metal wire, or use a slightly higher gauge wire that will fit, and place it inside the 2nd metal tube. This will be used to puncture the balloon. Lastly, fill the 2-liter with soda, and screw the cap/rods on. Now you should have a full 2-liter of soda, inside of which is an air-filled balloon surrounding 4 Mentos. At your leisure, you can push the sharpened wire through the 2nd tube to puncture the balloon, instantly surrounding the Mentos with soda in a closed environment. The only flaw in this design is that soda will shoot out of the wire tube at a high velocity once the bubbling occurs, so the apparatus will need to be initiated within one of your hand bags.

Chris said...

Pop a balloon, you has a ball of cola?

Matt said...

I had the same idea about the balloon - but maybe rather than try and pierce it, chemically compromise it. I have discovered serendipitously that the 'Air Therapy' product from http://www.miarose.com/ causes balloons to burst. Then again, they're under more pressure when inflated. Still, there must be a chemical means to cause the cola containment sphere to gracefully wither.

Rustin H. Wright said...

Nice. Very nice. As a guy who was very into liquids in microgravity in high school, I'm delighted to see the field turn up again. Makes me want to send y'all my old copy of Prandtl though perhaps the work of C.V. Boys would be more in the spirit. One suggestion; you might want to refer to the 'aircraft" so as to distinguish it from the field of reference.

Happy menticulation!

-Rustin

realman10000 said...

Why not create a sort of glass sphere with a chamber in the center with a mentos attached and pumps placed equidistant on the ends of the x,y, and z axis that direct the soda into the center where the mentos is. also there would need to be a vent somehow for the reaction.

Anonymous said...

Cut a coke bottle in half horizontally (so you have a top with a nozzle and a bottom with the base), wrap duct tape around the "wound", and fill with cola. Then, in minimum gs, unwrap the tape and pull the two halves of the bottle apart. Though I don't know how to get the mento in there. Maybe... toss it gently into the floating cola?

Anonymous said...

Please remember you are NOT weightless or 0g. You are inside object that is falling/flying such that your interaction with that object appears to be 0g. All objects in that environment have this appearance. There is no "left over" g. Just the imperfection of manufacturing this environment.

Even the space shuttle is not in a 0G. It just the orbit (tangential velocity to direction of gravity's "pull") places the objects in what appears to be 0g. Or better words "constant free fall" "free fall" is not 0g, it just you "never" hit bottom.

Anonymous said...

For manual control you could use IR to transmit the signals (if the camera is not affected by having a too weak IR filter)

Good Luck!
Georg

Anonymous said...

Servos seems like overkill. How about a stick that pokes out of the box and you turn manually? You can seal the hole with felt & grease or rubber grommets.

Nick Phillips said...

What you need to insert the mento is a long tube with the end sealed with some kind of plastic/rubber "sphincter" (I can think of several ways this could work). The mento is sealed inside the tube, with something some kind of rod inserted in the other end of the tube to push the mento through the hole in the elastic. Like your tube is laying a mento egg. If you insert the tube so that the tip is in the centre of your blob of cola before laying the mento, "that should work"...

Well, *I* know what I mean ;-)

Anonymous said...

This is a cool experiment.

It's hard to believe that a company in the business of providing a "zero G" environment would not have an autopilot that could do the job. As long as your ball of soda is floating without hitting anything, there are no extraneous forces acting on it. It's in free fall with no wind and should give you the effect you're after.

Anonymous said...

It's like a baloon! and then... something happens!

Although the relief of preassure from the baloon might cause the cola bubble expand in some way, but I bet somebody has already done it, you can look it up.

Ger said...

Does the cola HAVE to be in a free floating sphere?

I would think that if you made a 6 inch cube with a slide off or hinged lid and fixed that within a 20 inch or so cube you could easily rig an arm to swing the Mentos into the center of the inner cola containing cube. If one side of the small cube was actually also the outer wall of the outer cube you would also likely be able to get a clearer video.

Granted a free floating sphere of cola would look cooler but achieving that would likely be a bit more difficult.

A free floating sphere would also be prone to wanting to float around and possibly hit the closest surface of your outer vessel. A fixed cube would keep most of the cola from wandering off.

Anonymous said...

As others have mentioned, I think the balloon idea will disturb the sphere too much. If it were me, I'd build an open sphere space out of 2 hoops (90 deg to each other at the N/S poles), mount 8 rigid tubes to the hoops (4 each sphere at 90 deg equal distant, 45 deg offset from the N/S poles of the hoops) all directed to the middle of the sphere space from all directions. Connected to the rigid tubes would be flexible tubing (all equal length) to bring the cola to the center of the sphere space. These flexible tubes would connect to a manifold, then to the 2 liter cola bottle, and a practiced squeeze on the bottle could deliver just the right amount of cola to the sphere. In zero g, having the cola meet in the middle from 8 directions from the two hoops should cancel out the motion and leave it near the center of the sphere space. The mentos could be prepositioned in the middle of the sphere space and have some manual adjustment like experiment 1 in case one of the tubes malfunctions or residual gravity moves the ball of soda.

Hannibal said...

I hate to sound overly simplistic here, with all the well thought out comments, but here's my 2 cents worth...

If you place one or more of the Mentos on say a small diameter knitting needle (pierced through the center, like the string that was used) then just immerse the "Mentos stick" of Mentos into the full 2 liter bottle, won't that have the same effect as you're looking for? The knitting needle should be a minimum of say 10" long, so as to get full immersion into the bottle. According to my wife, the smallest size/gauge available is a "5", although with some searching, she says you can find as small as a "2". This is a FAR less expensive way to complete your experiment than using servos, etc.

Just a thought guys... looking forward to upcoming updates. This stuff is fascinating. :)

Anonymous said...

Why not strap a tube with a spring to the top of the coke bottle loaded with mentos with a gate? release the gate and the mentos are pushed by the spring into the bottle.

Joe

opie said...

as for creating a sphere of cola, i remember a water balloon that was popped in zero G creating a near sphere. then thrust a mentos into the sphere. would be a hell of a set up to do in a safety bag, but do-able.

http://spaceflightsystems.grc.nasa.gov/WaterBalloon/

about 1/3 the way down. donno how the carbonation would affect the experiment. but an idea on how to fill it. put a balloon over a 2 or 3 liter tightly (like a water hose end) and compress the bottle till balloon is filled. this should transfer the fluid with minimal shaking and at a controllable pressure.

also, make sure that the mentos is not connected to the plane... free floating cast member maybe.

Richard said...

Didn't the Mythbusters show that removing the cola from the bottle changes the dynamics of the cola? It doesn't react nearly as much to mentos after being removed from its bottle.

Valisk said...

No such word as menticulation

Anonymous said...

One idea I haven't seen yet is coating the mentos in something that the coke would dissolve in a set period of time (TBD in earthside experiments). Then you could load everything either before boarding the plane or while getting to zero-g, set up the camera,and just wait for the coke to eat through the coating.

Ron said...

Remember how Tylenol used to come in little capsules that would dissolve in your stomach? Can you find/make a version of that same "capsule" stuff which dissolves in Diet Coke, instead of stomach acid?

If you can find it, and you can wrap your Mentos in it, you could insert the encapsulated Mentos into the Diet Coke *before* reaching zero G -- timing it such that the coating would dissolve just after you hit zero G. Then, hopefully, once you hit free fall, you'd be free to simply watch the menticulation unfold; you wouldn't have to do much.

You could even use one or more of the earlier parabolic arcs in the flight to fine-tune the timing.

Also -- after a few minutes of Googling and Wikpediing, I found Wikpedia's entry for gelcap, which offers some clues about where to start.

Anonymous said...

If there are no radios (RF) allowed on board, could you potentially trigger via IR? Like a TV remote control?

Anonymous said...

The balloon design wont work. In coke CO2 keeps solved because of a bit of overpressure that can not be maintained by a balloon. You probably will end up with a nice sphere of 'stale' coke that is unlikely zo react with mentos at all. kg, alx

BTW: I digg that mad scientist style of basic (aka at first impression useless) research ;-)

Anonymous said...

How about a balloon made of (a very thin film of) gelatin? If you time it right it could be fully dissolved exactly when you need it.

On the other hand I any balloon-popping method would be able to avoid the cola exploding in all directions...

Curtis said...

to ram: creative idea, but when you submerge your bag of gas, it loses volume do to increased pressure.

If you have the money to fly to vomit-comet, you can probably afford a gas buret to get a far more accurate measurement of gas volume (and of course you'd also need to local barometric pressure and the temperature at the time of the reading... refer to the "ideal gas law" http://en.wikipedia.org/wiki/Pv%3Dnrt which is actually not perfect but ought to be good enough for this....

Forrest Cavalier said...

Using an artificial light source gives you some freedom. Can you construct a single mount that positions the camera, light source, and the vessel containing the coke? Would this also eliminate the requirement to adjust the camera orientation and focus?

With such a setup, once on the arc, you reach through to open the vessel and insert the mento on a stick.

Toby said...

NASA did a very similar experiment on the ISS. They used alka-seltzer in a water bubble. I'm guessing the mentos/coke reaction is more violent but you may be able to learn something from the way NASA did it: youtube video (towards the end)

lccarson said...

In the spirit of brainstorming, I'm reminded of the scene in Spider and Jeanne Robinson's novel, Stardance, where a character plays with liquids in microgravity. Didn't he contain one blob in a hoop? Okay, physics folks, does that work? Does that work with cola? Then you've got a lens-shaped blob anchored to a frame, kind of like blowing bubbles. Easier target to hit with a Mentos.

Plus now I want to see what all the bubble-blowing stuff looks like in microgravity.

Tim said...

Switch to a clear soda. Perhaps a tonic water in a glass bottle for better filming. Mount a/some Mento(s) on a straw mounted to a second lid so that when the lid is on the mentos are insid the bottle. Encapsulate the mentos to keep them away from the soda with an operating arm through the straw that will open the capsule. Put a condom over the lid. In flight, open two bottles, top one off to eliminate as much air as possible, put on the rigged cap, start filming and open the capsule. The straw will vent excess pressure so a buildup of pressure won't effect your results, the condom isn't necessary except for containment so nothing disturbs the camera's view. Also can be done on mother earth as a control.

Max said...

My Idea: Get a clear acrylic pipe cap the bottom and fill it with soda.
Push the mentos through a latex sheet and tie it off. This should prevent it from coming in contact with the coke.
Mount the latex sheet to the top of the pipe.
When you untie the string and push the top of the mint, it should shoot downwards into the soda.
To accurately measure the amount of gas produced you could cut a hole in the side leading to a large balloon or other airtight container.
(this idea might not transfer to words very well, but I have a very clear mental image and I'm quite sure it would work)

Anonymous said...

If you have a sphere of cola, shouldn't a round ball of mentos be used as well?
I like the melting coating idea as well.