Article (Scientific journals)
A more thorough analysis of water rockets: Moist adiabats, transient flows, and inertial forces in a soda bottle
Gommes, Cédric
2010In American Journal of Physics, 78 (3), p. 236-243
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Keywords :
Water rockets; rocket propulsion
Abstract :
[en] Although water rockets are widely used to illustrate first year physics principles, accurate measurements show that they outperform the usual textbook analysis at the beginning of the thrust phase. This paper gives a more thorough analysis of this problem. It is shown that the air expansion in the rocket is accompanied by water vapor condensation, which provides an extra thrust; the downward acceleration of water within the rocket also contributes to the thrust, an effect that is negligible in other types of rockets; the apparent gravity resulting from the acceleration of the rocket contributes as much to water ejection as does the pressure difference between the inside and outside of the rocket; and the water flow is transient, which precludes the use of Bernoulli’s equation. Although none of these effects is negligible, they mostly cancel each other, and the overall accuracy of the analysis is only marginally improved. There remains a difference between theory and experiment with water rockets.
Research center :
Department of Chemical Engineering
Disciplines :
Physics
Author, co-author :
Gommes, Cédric  ;  Université de Liège - ULiège > Département de chimie appliquée > Génie chimique - Génie catalytique
Language :
English
Title :
A more thorough analysis of water rockets: Moist adiabats, transient flows, and inertial forces in a soda bottle
Publication date :
March 2010
Journal title :
American Journal of Physics
ISSN :
0002-9505
Publisher :
American Association of Physics Teachers, Melville, United States - New York
Volume :
78
Issue :
3
Pages :
236-243
Peer reviewed :
Peer Reviewed verified by ORBi
Funders :
F.R.S.-FNRS - Fonds de la Recherche Scientifique [BE]
Available on ORBi :
since 17 May 2010

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