Soda and Mentos
Joey and his friend Colton put together a fun experiment for his 5th Grade Science Project. Somehow they learned that if you add a roll of Mentos to a 2 liter of soda, a reaction occurs that causes the soda to rocket out of the bottle. We don't have a video of the experiment itself, but here's an overview and video of how it works.
Below are 3 additional videos. The first is of the project itself. The second is Joey explaining the project to us, and the third is Joey and Colton explaining the project to one of the judges. Though you can't hear much on the third video, we thought watching Joey's interaction with his friend and the judge was pretty impressive.