Theoretical and Experimental Analysis of the Physics of Water Rockets

When I read the title of this paper, my first remark was "No!!".

Anyone reading this blog for a while would have seen my entry on The Physics of Human Bottle Rocket, which includes a crazy video of a crazy man being strapped to one of these bottle rocket. So now it appears that there is a paper describing water rockets. I'm not sure if it is the same thing, but it is amusing nevertheless.

R Barrio-Perotti et al., Eur. J. Phys. v. 31, p.1131 (2010).

Abstract:A simple rocket can be made using a plastic bottle filled with a volume of water and pressurized air. When opened, the air pressure pushes the water out of the bottle. This causes an increase in the bottle momentum so that it can be propelled to fairly long distances or heights. Water rockets are widely used as an educational activity, and several mathematical models have been proposed to investigate and predict their physics. However, the real equations that describe the physics of the rockets are so complicated that certain assumptions are usually made to obtain models that are easier to use. These models provide relatively good predictions but fail in describing the complex physics of the flow. This paper presents a detailed theoretical analysis of the physics of water rockets that concludes with the proposal of a physical model. The validity of the model is checked by a series of field tests. The tests showed maximum differences with predictions of about 6%. The proposed model is finally used to investigate the temporal evolution of some significant variables during the propulsion and flight of the rocket. The experience and procedure described in this paper can be proposed to graduate students and also at undergraduate level if certain simplifications are assumed in the general equations.

Published 29 July 2010

Note that you may obtain a free copy of the paper within 30 days of online publication.


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