Episode 57: Diet Coke and Mentos, Postage Stamp on a Helicopter
- Diet Coke and Mentos: CO2, aspartame, potassium benzoate, and caffeine in the Diet Coke, gum Arabic and gelatin in the Mentos, as well as the tiny pits on a Mentos candy (nucleation sites) are responsible for the explosive reaction of Diet Coke and Mentos
- Postage stamp on a helicopter: mythbusted. If you stuck ~8000 postage stamps, you could crash a copter, but a single postage stamp won't make a difference.
- Methane soap bubbles, homemade smoke bombs, dry ice bombs, and hydrogen potato chip bombs can be as spectacular as Diet Coke and Mentos, but not nearly as safe or easy to procure ingredients for.
The Diet Coke and Mentos segment wasn't a myth, and they admitted as much. They wanted to investigate all the varying explanations for the reaction they had heard. They first investigated the ingredients of Diet Coke and found that CO2, aspartame, potassium benzoate, and caffeine all contributed to the reaction. They next tested the ingredients of Mentos and isolated gum arabic and gelatin as causes. They also found that the small pits on Mentos contribute to the reaction by providing nucleation sites. With all this information in hand, they decided to build a rocket, which was a big failure. They then did a spout height competition, which beat the unofficial record of 18ft (they got 29+ft). Finally, they tried to create their own fun Internet craze that would be fun (i.e. explosive), safe, and easy to put together, but failed. They had fun down though: flaming columns of methane soap bubbles, homemade smoke bombs, dry ice bombs, and hydrogen potato chip bombs.
As with many of their myths, they first started off with some scale models tests. With a 1/7th scale R/C helicopter, they weren't able to get any deflection of the blades under the normal conditions of the myth. With an 8000 postage stamp equivalent, they got the copter to shatter into pieces. They finished their testing with an actual helicopter from the Oakland Police Department. The copter was able to fly with a postage stamp on the top and tail boom rotor, and a velocimeter showed that there was very little different in later motion with the postage stamp applied. busted
Diet Coke and Mentos
Investigate: why does Mentos cause Diet Coke to geyser?
See also: pop rocks + soda myth
This isn't a myth as they know it occurs, but the MythBusters wanted to determine which of the various explanations for the explosive powers of Mentos and Diet Coke is correct.
The Diet Coke and Mentos craze can be credited to the Eepybirds of Maine, whose video of choreographed fountains spread like wildfire across the Internet. Their video used 101 bottles of Diet Coke 523 Mentos.
Adam's tried dropping in four Mentos into Coke for his very first time: "I think we're gonna have to try that a whole bunch more times"
What in the Diet Coke is responsible for the reaction?
Jamie degassed the soda by sticking a balloon over the top of soda bottle and shaking it until all the CO2 had been removed. Unsurprisingly, dropping in Mentos after that had no reaction.
They wanted to figure out what else in the Diet Coke might be responsible for the reaction, so they next they got some soda water, which is just CO2 and water. They dropped Mentos into both the soda water and a Diet Coke bottle: both reacted, but the Diet Coke definitely shot higher into the air. That meant that there were ingredients other than CO2 at work.
Adam decided to test each of the individual ingredients in Diet Coke to see if any of them caused a greater reaction. The baseline was 3", which was how high soda water by itself reacted . Each ingredient was mixed in with soda water and tested:
- Aspartame (artificial sweetener): the reaction was 20x higher than soda water alone (~60")
- Anhydrous Citric Acid: nothing
- Phosphoric Acid: nothing
- Potassium Benzoate (preservative): the reaction was definitely stronger -- there was even a reaction from the soda water when the preservative was first added.
- Caffeine: also caused a stronger reaction
Based on Adam's experiment, they isolated out four ingredients of Diet Coke that were important: CO2, aspartame, potassium benzoate, and caffeine.
What in Mentos is responsible for the reaction?
Adam tested the various ingredients of Mentos and found that gum Arabic and gelatin as two likely candidates. Both ingredients caused the soda water to overflow, though neither caused a geyser.
They also tested the theory that the Mentos reaction is also due to the fact that Mentos candies are pitted, which provides nucleation sites, i.e. areas where the CO2 can convert to gas bubbles. The Mentos candies also sink, which cause many bubbles to form at the bottom of the bottle.
They got some Mentos flavors that have a smoother coating (wax coating). The ingredients of these smooth Mentos are otherwise the same, yet the smooth Mentos didn't cause any reaction when dropped into the soda water.
The ingredients of the Mentos and Diet Coke, in combination with the nucleation sites, cause a cascade effect by which the CO2 in the soda is quickly released.
Mentos + Diet Coke Rocket
With all the ingredients of the reaction isolated, they decided to build a rocket. They went with a four-bottle design that had PVC tubing to redirect the force of the expelled CO2 downward. They also created a release mechanism using magnets inside of the tubes to hold the Mentos until launch.
In their first test launch, there were tons of leaks, so instead of moving upwards, the rocket contraption simply rotated around. They also felt the design was too heavy, so Jamie worked on lightening the build. Adam decided that mounting a Diet Coke bottle the lathe was a fun idea -- perhaps he is harboring a secret desire to be killed by Jamie. Predictably, the Coke exploded all over the lathe.
Jamie's new design was a single-bottle contraption. It failed to launch, even when they stuck it on a ramp so it could shoot off at an angle. They tried many other variations that only did slightly better and eventually Adam resorted to slamming Diet Coke bottles on the ground to get them to explode.
Diet Coke/Mentos Rocket: failed
Jamie and Adam decided to face off in a challenge to see how could shoot the highest Diet Coke + Mentos geyser spout. The unofficial record is 18 ft. Adam started off by making a nozzle that he quickly fashioned into a light-saber ("plasma sword") handle (Adam: "Except instead of a limited beam of pure plasma, it's soda! Yeah!"). Jamie had a competing nozzle design that didn't have a built-in release mechanism, so it was a bit more difficult to attach (Jamie: "They keep trying to get me to compete and, you know what, I don't like it"). Both Adam's and Jamie's nozzles went 23 ft. Jamie ended the competition by turning himself into a geyser: he poured some Diet Coke into his mouth, popped in a Mentos, and spouted forth.
Adam and Jamie next combined forces to build a spout. The first attempt went 29 ft, but Jamie had trouble holding the spout on. They did another attempt, which went higher. They next tried some other ingredients based on their earlier studies. They hit pay dirt with rock salt went 34ft.
- Unofficial record is 18 ft
- Adam's nozzle: 23 ft
- Jamie's nozzle: 23 ft
- Adam and Jamie's nozzle (with Mentos): 29+ ft (they didn't report the height of the second try, which was higher)
- Adam and Jamie's nozzle (with rock salt): 34 ft
The next ‘big' thing
Adam and Jamie wanted to start an explosive Internet craze of their own.
Flaming columns of methane bubbles (Adam's contribution): You bubble methane up through soapy water. The methane causes a column of bubbles to rise up into the air. You can then set the column on fire to get a mid-air explosion. Their first attempt formed a lop-sided column, which started to fly away as Adam released it, but not too far away: both the bucket of bubbles and the flying column went up in flames when lit. Their second attempt was even better: the built ~4ft column, which went up with a nice flourish.
Adam: "I have to say, for my money, that rivals the candy and soda. However, the candy and soda that's safe enough for any four year old to do --- I mean at least they're from everything except for getting yelled at by their parents. This one, it's not safe for pretty much any of our viewers. We've done it, now you don't have to."
Smoke bombs (Jamie's contribution): you cook salt peter and sugar until its hot and molasses-y, pack into some molds, and stick some matches in it with the match heads out so they can be lit. Adam tried to make a larger batch than Jamie, which ended up going up in red flames on the stove (Adam: "So that‘s what can happen… And that‘s why you don‘t try this at home").
Adam decided to use the smoke bombs to get revenge and Kari and Tory for electrocuting him in Baghdad Battery "Well, all I gotta say is, ‘Payback is rough.'" Adam tossed one of the smoke bombs in on the build team as they were testing another experiment (possible Exploding Pants), but it didn't go as well as Adam hoped. In a fine display of their training, Grant immediately reach for his ear protection and Tory put on safety glasses, but it wasn't really necessary. Tory: "is it a hockey puck. It's a flaming hockey puck." Kari put it out with a fire extinguisher and they shooed Adam by shooting him with the extinguisher.
Hydrogen and potato chip bomb: You poke a hole in the top and bottom of a Pringles can, pump in hydrogen gas from the bottom, and set it alight. The tin container will get blown off, but the chips will be fine. Hydrogen is lighter than air, so it will rise out through the top. When you light the top, it will burn and cause air to be sucked in from the bottom. Eventually the air/hydrogen mix will be right, and the flame will go down into the can and cause it to explode. In their first test, Jamie set it on fire with a lighter, which turned out to be a bit of a mistake: the can exploded immediately with a loud pop, and Jamie wasn't wearing ear protection -- he seemed a bit annoyed at Adam, who had told him he didn't need any. The chips weren't quite undisturbed, though they weren't blown into bits. For the second try, they put on ear protection and got a longer pole to ignite it with. This time it went closer to spec: the hydrogen lit with a hard-to-see flame and burned for awhile, and then it suddenly popped. They tried it a couple more times, and it did leave the chips relatively intact. Adam: "…the results of blasting the can off a stack of chips and leaving them almost intact, I mean, it's just makes me smile just thinking about it." The hydrogen potato chip bomb is fun, but most people can't get hydrogen.
Dry ice bomb (Adam's suggestion): with a 2-liter bottle, dry ice and water, you can make a bomb. The dry ice is turned into gas by water, which builds up the pressure quickly. Adam stuck on the red safety suit, as this one is a bit dangerous. Jamie setup the bomb and ran away. It took awhile, but the soda bottle blew up into little shrapnel. According to Jamie and Adam, it was quite loud.
Adam and Jamie admitted they couldn't come up with anything as great as Diet Coke and Mentos, on the grounds that Diet Coke and Mentos is: safe, fun, and uses household ingredients that are easy to find. Everything Adam and Jamie tried was fun, but didn't do as well on the other criteria.
Postage Stamp on a Helicopter
Myth: A postage stamp stuck on the rotary blade of a helicopter will cause the rotors to unbalance and cause a helicopter crash.
They went to Century Helicopter Products in San Jose, where they picked up a trainer copter and a 1/7th scale model of the Oakland Police copter they were going to test.
Tory: "How hard is to fly these?"
Paul Pan: (Century Helicopters) "We tell customers that you're guaranteed that you're gonna crash"
Indeed, Grant tried to fly the trainer at the store and promptly crashed into the door. Grant and Tory later practiced with the trainer some more, but neither quite got it down.
In order to measure the deflection of the blades with postage stamps attached, they secured the 1/7th scale police copter to the table and put a scale up behind it. They first tested the blades without any stamp attached, which verified that the blades were level. They then attached a 1/7th scale postage stamp, which didn't show any deflection of the blades on the high-speed camera.
Tory: "I say we destroy it"
Grant: "This is why we can't have anything nice."
Grant attached a weight to the end of one of the rotor blades that was equivalent to 8,000 postage stamps (at 1/7th scale). The helicopter rocked the table back and forth until the tailor rotor fell off and the entire helicopter ripped off the table and fell to the floor in pieces. NOTE: It appeared from some of the clips that they did some more testing in-between the single postage stamp and the 8,000 postage stamp equivalents, but they didn't report the results.
Testing with an Oakland Police Department copter
They talked to Sergeant Rick Hassna of the Oakland PD and said that the rotors were sensitive to anything on them, including balloons, dust, and paint.
Chad Kuenzinger, rotor balance specialist, hooked up a velocimeter to the side of the copter below the rotors, where it could measure the lateral vibrations. Rick flew the copter into a hover position both with no postage stamp on the blade and with a single postage stamp:
- No postage stamp: 0.173 in/s (ips)
- Single postage stamp: 0.174 ips
In other words: mythbusted
For completeness, they put a postage stamp on the tail boom rotor and the top rotor and went for a flight. Their pilot felt no difference whatsoever.
Top and tail rotor and postage stamp: myth busted