Mentos & Diet Coke

you could use your cell phone and an app called " Rocklogger". One of the subroutines of the Rocklogger actually turns your cell phone into a level and surveying compass.

HERES A QUICKIE TUTORIAL

1.Measure the distance from the one holding the cell phone to the place where you shoot off the Mentos/coke (Like NEAR A WALL would be best)

2. Measure the distance from the ground to the phone's eye level of whoever is taking the measurement. (that is the actual zero ground level for your surveying app)

3. when the mentos foam is shot off, someone has to measure the maximum angle from your eye level to the highest elevation the foam "fountain" achieves.

3.Use the trig functions in the Rocklogger app and(using a TAN function) solve for the right triangles elevation.(Then add the additional elevation of the ground to ye level of the measurer.




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OR, if you have a hunter in the family. One who has a distance measuring range finder , you can accomplish the same as the app (except there would be a few extra steps)
Rocklogger is a student grade app that costs about a buck at the app store. It has a lot of other science and surveying tools on board so your kid can have some fun with it and HAVE EM BE OUTSIDE MORE.

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In my mind Using any formulas that have "time components" require you to know how fast the mess is going and I don't think that's gonna work unless you know the vertical elevation in discrete units.

Heres a little video on YouTube that is about measuring the height of a tree using trig functions.
(Using the cell phone app is so "today" though"
http://www.youtube.com/watch?v=-2w7Mdq5C58

First, create a hypothesis including the variables you think are important in determining the height of the plume. Doing this requires some understanding of what is happening when Mentos hits Diet Coke. Once you have the theory part done, identify what you think are the important factors.

Does the quantity of Diet Coke matter? (I think it might not.) Do the number of Mentos dropped matter? (Probably) What if you grind them up first? (Might matter a lot. Can you figure out why?) Does the size of the opening on the container matter? (Absolutely). How about the age and temperature of the Diet Coke. (Very likely)

Once you identify the variables you want to test, you design your experiment by testing various conditions while holding the other variables constant. That will allow you to test your ideas. Does the experimental data match your hypothesis? If not, revise your hypothesis and try again.

the chemistry of this violent reaction is related to 2 physical features of the entire system

1Mentos candies have a high surface area due to their "swiss cheese" like structure

2Aspartme in the diet soda, keeps surface tension down so the reaction is more violent.

The game is about measuring the height of the jet that erupts from the bottle(any size ). On one tv show (MYTHBUSTERS), they achievd an eruption of over 30 feet.
You can jack up the reaction with a teaspoonful of rock salt then the mentos

@farmerman, It is the right solution you have given, thanks for sharing this.

Imagine there will be a plethora of x-factors effecting the height (orientation of the Mento as it first hits the diet Coke (i.e. how many pits contact the diet Coke initially starting the reaction like,) local humidity and temperature, local gravity maybe (gravity varies place to place believe it or not,) that any formulae woudl be less than completely reliable. So short of high speed camera and a known height measure to compare it to you'd only be getting an approximation.

that looks just really funny