- Forces and Motion
This demonstration unleashes the power of candy and soda to propel a rocket car.
Rocket propulsion works because of pressurized gas. When the gas escapes the rocket (going down), it pushes the rocket up. If we turn the rocket on its side, the gas will push behind the rocket to propel it forward. Put some wheels beneath it and you have a rocket car! We can use a variety of methods to create pressurized gas. This activity uses Mentos and Diet Coke.
Mentos and soda “Rocket Fuel”
Soda is fizzy because it contains molecules of carbon dioxide (CO2). When it’s poured into a glass, the carbon dioxide molecules separate from the water by forming bubbles—a process called nucleation—and escaping into the air. After a while, the soda will go flat, but this process takes some time and isn’t powerful enough to propel our rocket car. By adding Mentos candy to the soda, we can speed up the nucleation process to cause a geyser powerful enough to spray high into the air or, in this case, move a rocket car.
Gum arabic on the Mentos’ surface breaks up the surface tension of the water in the pop. The surface of Mentos is rough and filled with tiny dimples and holes that are great spots for nucleation because of how they increase the surfacearea available for reaction. When Mentos and soda come into contact, lots of CO2 bubbles form very quickly and cause a "geyser"-like eruption.
Although any carbonated beverage will produce a similar effect, we recommend Diet Coke for two reasons:
- Aspartame, the artificial sweetener in Diet Coke, speeds up the reaction even more because water with aspartame in it has a lower surface tension than sugary water (this allows the bubbles to escape more easily)
- It’s much less sticky to clean up!