Engineering ToolBox - Resources, Tools and Basic Information for Engineering and Design of Technical Applications!

Jet Propulsion

Calculate the propulsive discharge force or thrust induced by an incompressible jet flow.

Sponsored Links

The velocity out of a free jet can be expressed as

v2 = (2 (p1 - p2) / ρ)1/2                              (1)


v2 = velocity out of the jet (m/s)

p1 = pressure before the jet (N/m2, Pa)

p2 = ambient pressure after the jet (N/m2, Pa)

ρ = density of the fluid (kg/m3)

Note! - the density ρ is constant in incompressible flows and the equations are valid for liquids (like water) but not for gases (like air).

The flow volume out of a jet can be expressed as

q = A v2                                (2)


q = volume flow (m3/s)

A = orifice area of the jet (m2)

The propulsive force or thrust induced by the jet can be expressed as

F = ρ q (v2 - v1)                                (3)


v1 = jet velocity (m/s)

If the jet is not moving

v1 = 0

and (3) can be expressed as

F = ρ q v2                                    (3b)

- or alternatively with (2)

F = ρ A v22                                  (3c)   

Substituting v2 with eq. (1) in eq. (3c) - the propulsive force or thrust induced by a jet not moving (v1 = 0) be expressed as

F = 2 A (p1 - p2)                                 (4)

Example - Propulsive Force

garden hose jet flow

Water flows through a garden hose with diameter 15 mm. The water pressure just before the outlet is 4 105 Pa (abs) and the atmospheric pressure is 1 105 Pa (abs).

The outlet area of the hose can be calculated as

A = π ((15 mm) (0.001 m/mm) / 2)2

   = 1.77 10-4  (m2)

The propulsive force can be calculated as

F = 2 (1.77 10-4 m2) ((4 105 Pa) - (1 105 Pa))

   = 106 N

Water jet propulsion

Sponsored Links

Related Topics

  • Fluid Mechanics

    The study of fluids - liquids and gases. Involving velocity, pressure, density and temperature as functions of space and time.

Related Documents

Sponsored Links

Engineering ToolBox - SketchUp Extension - Online 3D modeling!

3D Engineering ToolBox Extension to SketchUp - add parametric components to your SketchUp model

Add standard and customized parametric components - like flange beams, lumbers, piping, stairs and more - to your Sketchup model with the Engineering ToolBox - SketchUp Extension - enabled for use with older versions of the amazing SketchUp Make and the newer "up to date" SketchUp Pro . Add the Engineering ToolBox extension to your SketchUp Make/Pro from the Extension Warehouse !

Translate this Page

Translate this page to Your Own Language .

About the Engineering ToolBox!

Privacy Policy

We don't collect information from our users. More about


This page can be cited as

  • The Engineering ToolBox (2013). Jet Propulsion. [online] Available at: [Accessed Day Month Year].

Modify the access date according your visit.


3D Engineering ToolBox - draw and model technical applications! 2D Engineering ToolBox - create and share online diagram drawing templates! Engineering ToolBox Apps - mobile online and offline engineering applications!

Unit Converter


Sponsored Links