Taking the cap off and dropping them in is probably a bit dangerous.
Doesn’t look particularly dangerous to me, unless you include the danger of running into one of those posts (or off the edge of the roof) in attempting to get away from the Coke-geyser.
I was including the possibility of getting Coke in the eye. That can’t be good.
I’ve been doing this in the backyard to entertain the kids for a month or two now. But try as I might I can’t get more than about a four foot geyser.
Anyone have any tips on getting the whole ‘shoot to the sky’ effect going?
Won’t drilling the small hole in the cap make your geyser higher and stronger? snicker That sounded way dirtier than I intended.
I don’t know all the fancy technical terms, probably something about “occlusion” and “flow patterns” and stuff, but I know when I put my thumb over the hose nozzle, it makes it spray harder and further, without changing how much or how fast the faucet is putting water into the other end of the hose.
I tried this at my buddies house. His kids loved it. Rolled a piece of paper up and stacked the mentos inside that, with another piece of paper below the tube to keep them from falling in. Pulled the paper out and ran. Yeehaw fun.
WhyNot, I’m glad I’m not the only one finding this discussion getting a little risque. Oh well, you know what they say - a dirty mind is a terrible thing to waste. 
Bastard, you stole my joke.
If you drill a hole in the Mentos, and put a string or wire through them, then drill a hole in the cap to the soda, and put them under the cap, holding the string or wire taut, then screw the cap back on, you can then release the string or wire, they will drop into the soda, which will then be forced out of the hole in the cap, rather than the much larger mouth of the bottle. They also recommend trying drilling multiple holes in the cap for fancier effects.
Here’s a video where a bunch of guys use the reaction to rocket the bottles skyward.
I also saw a similar one where they show them removing the outer paper wrapping of the mentos but leaving the inner wrapping on before they drop it in. I assume that it only takes a few moment for it to just come off by itself in the fluid.
If you watch the video I’d reccomend turning the volume down or off. That song is annoying.
My chemistry professor confirms this explanation, FWIW.
Darn, beaten barely into the thread by a real chemistry professor. I’m just a HS chem teacher, which puts me off the ladder of the rankings of scientists. I think I get to be in the room with the ladder, is all.
Yeah, it’s the nucleation sites. The pressure comes from letting out all of the dissolved CO2. That bottle gets really stiff. I managed to make a couple decent rockets for my classes. I also did it with Certs when 7-11 didn’t have Mentos. It’s just all a way to get out all the dissolved gas inside a minute.
I did that one.
It made a neat spray about 8 feet high at first, then it settled down to a foamy 2-foot arc that lasted about 10 seconds.
It was kinda neat.