Tuesday, July 29, 2008

Diet Coke and Mentos: Soda-Candy Explosions

Tonya Coffey and her students reported "an experimental study of the Diet Coke and Mentos reaction (made famous in a 2006 Mythbusters episode), and consider(ed) many aspects of the reaction, including the ingredients in the candy and soda, the roughness of the candy, the temperature of the soda, and the duration of the reaction." (Am. J. Phys., 2008, 76(6), 551 - 557)


1. The Mythbusters correctly identified potassium benzoate and aspartame as key ingredients in the Diet Coke–Mentos reaction. (Static water) Contact angle measurements were used to show that these ingredients reduce the work required for bubble formation, allowing carbon dioxide to rapidly escape from the soda. The small amount of caffeine in Diet Coke is unlikely to contribute significantly to the reaction.

2. The Mythbusters also correctly identified the roughness of the samples as one of the main causes of the reaction. The importance of sample roughness was shown by comparing SEM and AFM images of the samples to the explosive power of the reaction. Increased surface roughness implies a higher surface area to volume ratio, meaning that more growth sites should be present on per unit volume.

3. Samples which encounter less viscous drag and hence fall more quickly through the soda will cause a more explosive reaction. Also, for the same amount of mass lost, the eruption will be more dramatic when the reaction takes place over a shorter time.

4. Finally, hotter beverages result in a more explosive reaction. (A direct illustration of Henry's law and Le Chatelier's Principle)

The kinds of things researchers do...like popping candy into sodas and watching them fizzle and frazzle.

Thursday, July 24, 2008

Monty Hall Problem

This was shown in the movie 21. I got the answer wrong, and had a vigorous debate with a friend who was watching the show with me. It turned out she had taken a Math class on this in her undergrad. Bugger. She kept repeating - "conditional probability!".

Suppose you're on a game show and you're given the choice of three doors. Behind one door is a car; behind the others, goats. The car and the goats were placed randomly behind the doors before the show. The rules of the game show are as follows: After you have chosen a door, the door remains closed for the time being. The game show host, Monty Hall, who knows what is behind the doors, now has to open one of the two remaining doors, and the door he opens must have a goat behind it. If both remaining doors have goats behind them, he chooses one randomly. After Monty Hall opens a door with a goat, he will ask you to decide whether you want to stay with your first choice or to switch to the last remaining door. Imagine that you chose Door 1 and the host opens Door 3, which has a goat. He then asks you "Do you want to switch to Door Number 2?" Is it to your advantage to change your choice?

Friday, July 18, 2008

F-king word play (on a friday)

From the MSN conversation with A, who prefers to call herself HG:

HG: sigh, and I kinda like this other guy... but since I've graduated, probably won't see him much anymore. Lately been wondering if I should ask him out

tk says:
fuck him lah

HG says:

tk says:

HG says:
not so fast bah hahaha

tk says:

HG says:
I don't even know if he has a gf or not... he never talks about his love life. hahahah. And I'm kinda not the person to ask. Hmm, this is going to be difficult. haha

tk says:
Doesn't matter right. Just go for it. Fuck the other girl, if she exists

HG says: >_< I just want the guy. hahah. I don't think he's attached though. Nobody else has heard of a gf

tk says: Not fuck the other girl literally

HG says: lol. I know.

tk says: But ask her to scram. lol

HG says: hahahhahahahah

tk says: fuck in these cases, have multiple meanings

HG says: Wonderful word. hahah

tk says: Yup. One of the most wonderful words in the English language.

HG says: lol. Versatile too!

tk says: Exactly

I first came across this when I was in BMT more than a decade ago. Self-explanatory.