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Table of forces involved

Forces Balance Diagram / Diagramme d'équilibre des forces

1.Forces that help propel the projectile/rocket

Composantes de propulsion de la fusée

1. Water jet thrust

Forces au dues à l'éjection d'eau

2. Compressed air jet thrust

Force dues à l'éjection d'air

3.'Specific Impulse' continuity during jet phase.


Note: Any factors that improve or influence specific impulse.

  • Nozzle form and profile. 

  • Stability of duct during expansion and acceleration phases.

  • Dynamic fluid flow characteristics.

  • Reduced turbulent fluid flow.

  • Stable flight dynamics after decollage/launch.

  • Expansion control of fluid flow both before and after leaving the nozzle.

  • 'Tsiolkovski ' factor.


4. Elasticity of the plastic bottle.

Forces résultant de l'élasticité de la bouteille


2.Forces that resist the motion of the rocket/projectile

Composantes de résistance au mouvement de la fusée

4. Weight of the rocket M*g

Poids de la fusée

5. Aerodynamic resistance or Drag force

Résistance aérodynamique



6. Dynamic instability of rocket.

Instabilité dynamique de la fusée

7. Air turbulence or cross-wind that have components that oppose the trajectory of the rocket.

8. Meteo variables: Wind, rain, hail


Turbulences de l'air et vent latéral agissant en sens opposé à la trajectoire.

Facteurs météorologiques: vent, pluie, grêle

9. Physical parameters of the environment (medium) in which the projectile flies.

Density, viscosity, kinematic viscosity, temperature, pressure etc.


Paramètres physique du milieu dans lequel se déplace la fusée:

Densité, viscosité statique et dynamique, température, pression etc…

10. Jet stream fluid dynamics.

11. Nozzle efficiency /Turbulent flow

                Convergent, divergent

Dynamique du courant fluide

Rendement de la tuyère

  Convergente ou divergente

Created by John Gwynn and Prof Jean LeBot.

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This site was created on the 15th April 2003

 ©John Gwynn and sons2003 

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 as long as you give us proper credit (by referring to "The Water-Rocket Explorer" http://waterocket.explorer.free.fr).