Coke rocket making, the latest craze sweeping the internet has attracted the approval of the American Institute of Aeronautics and Astronautics (AIAA), which has updated its annual student water rocket competition to include the event.Teenagers have been swapping mobile telephone videos
of the experiment in which mint chewy candies are placed into a 2litre (64US Fl oz) bottle of diet cola to produce a chemical reaction that produces enough power to propel the contents up to 20m (66ft) into the air. If projected against the floor, the force can propel the entire bottle upwards. An example can be seen in the video clip below, one of thousands circulating the internet.
This phenomenon has attracted the attention of the AIAA's Student Branch at California State Polytechnic University, Pomona
, which runs an annual competition aimed at encouraging young people to think about the basics of aerodynamic design and propulsion. The addition of the compressed carbon dioxide "engine" gives the competition a new edge, Cal Poly Pomona says.
In the experiments undertaken by teenagers, Mentos brand mint confectionery reacts quickly with Diet Coca-Cola brand soda, causing an almost immediate release of the carbon dioxide stored in the soda. The escaping bubbles quickly turn into raging foam, and the pressure builds dramatically.
Theories are still being developed as to what exactly produces the violent reaction. Chemists theorised that a substance called gum Arabic in the Mentos breaks the surface tension of the soda, allowing the carbon dioxide bubbles to escape rapidly. However, gum Arabic is likely to be only a catalyst for a larger, physical reaction.
The explanation currently favoured by physicists is nucleation sites. Any liquid supersaturated with gas reacts on a nucleation site, or a place where the gas is able to form bubbles.
Nucleation sites can be scratches on a surface or specks of dust. Champagne glasses are designed to hold several thousand imperfections, or nucleation sites, to increase the creamy texture of the wine. The surface of a Mentos has thousands of nucleation sites in the forms of microscopic nooks and crannies on the surface. A sinking Mentos mint reacts as it falls, multiplying the propulsion effect.
It is not known whether any of AIAA’s older members will conduct further study into the effect for use in aero engines.