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Author Topic: rocket equation  (Read 8106 times)
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ahmedelshfie
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on: April 23, 2010, 12:01:45 am » posted from:,,Brazil

This applet created by Prof Hwang
Modified by Ahmed
Original project rocket equation



A typical rocket engine can handle a significant fraction of its own mass in propellant each second, with the propellant leaving the nozzle at several kilometres per second. This means that the thrust-to-weight ratio of a rocket engine, and often the entire vehicle can be very high, in extreme cases over 100.
It can be shown that the net thrust of a rocket is:

F_n = \dot{m}\;v_{e}

where:

\dot{m} =\,propellant flow (kg/s or lb/s)

v_{e} =\,the effective exhaust velocity (m/s or ft/s)

The v_{e} of a rocket engine is often almost constant in a vacuum, but in practice the effective exhaust velocity of rocket engines goes down when operated within an atmosphere as the atmospheric pressure goes up. In space, the effective exhaust velocity is equal to the actual exhaust velocity. In the atmosphere, the two velocities are close in value.

The Tsiolkovsky rocket equation, or ideal rocket equation, is a mathematical equation that relates the delta v with effective exhaust velocity and the initial and end mass of a rocket.

The equation is named after Konstantin Eduardovich Tsiolkovskii|Konstantin Tsiolkovsky who independently derived it and published it in his 1903 work(К. Э. Циолковский, Исследование мировых пространств реактивными приборами, 1903. It is available online http://epizodsspace.airbase.ru/bibl/dorev-knigi/ciolkovskiy/sm.rar here in a RARed PDF). It considers the principle of a rocket: a device that can apply an acceleration to itself (a thrust) by expelling part of its mass with high speed in the opposite direction, due to the conservation of momentum.

For any such maneuver (or journey involving a number of such maneuvers):

:\Delta v\ = v_\text{e} \ln \frac {m_0} {m_1}= v_\text{e} \ln \frac {m_0} {m_0-\dot{m}t}

where:
:m_0 is the initial total mass, including propellant.
:m_1 is the final total mass.
:v_\text{e} is the effective exhaust velocity. (v_\text{e} = I_\text{sp} \cdot g_0)
:\Delta v is \delta-v.

Units used for mass or velocity do not matter as long as they are consistent.

The following is a simulation of a rocket.
You can change
1. ratio: The initial rocket mass/ final rocket mass ratio,
2. pratio: propellant mass/ total mass
3. dmdt:\dot{m}
4. T: total acceleation time
5. u: v_{e}
It will draw it's displacement as a function of time x(t) and velocity as a function of time v(t).

Embed a running copy of this simulation

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Press the Alt key and the left mouse button to drag the applet off the browser and onto the desktop. This work is licensed under a Creative Commons Attribution 2.5 Taiwan License
  • Please feel free to post your ideas about how to use the simulation for better teaching and learning.
  • Post questions to be asked to help students to think, to explore.
  • Upload worksheets as attached files to share with more users.
Let's work together. We can help more users understand physics conceptually and enjoy the fun of learning physics!


* rocket equation.gif (18.99 KB, 715x526 - viewed 484 times.)
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ahmedelshfie
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Reply #1 on: April 26, 2010, 06:38:41 am » posted from:Uberaba,Minas Gerais,Brazil

Images from  http://en.wikipedia.org/wiki/Tsiolkovsky_rocket_equation


* 220px-Deltavs.svg.png (30.21 KB, 220x311 - viewed 424 times.)

* 220px-Rocket_mass_ratio_versus_delta-v.png (9.4 KB, 220x145 - viewed 411 times.)

* Var_mass_1system.PNG (0.91 KB, 405x128 - viewed 438 times.)

* Var_mass_system.PNG (0.91 KB, 405x128 - viewed 438 times.)
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ahmedelshfie
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Reply #2 on: June 26, 2010, 12:33:33 am » posted from:SAO PAULO,SAO PAULO,BRAZIL

The Tsiolkovsky rocket equation, or ideal rocket equation, is a mathematical equation that relates the delta-v (the maximum change of speed of the rocket) with the effective exhaust velocity and the initial and final mass of a rocket or other reaction engine.
The equation is named after Konstantin Tsiolkovsky who independently derived it and published it in his 1903 work.
It considers the principle of a rocket: a device that can apply an acceleration to itself (a thrust) by expelling part of its mass with high speed in the opposite direction, due to the conservation of momentum.
For any such maneuver (or journey involving a number of such maneuvers
History
This equation was independently derived by Konstantin Tsiolkovsky towards the end of the 19th century and is widely known under this name and ideal rocket equation. However a recently discovered pamphlet "A Treatise on the Motion of Rockets" by William Moore,,shows that the earliest known derivation of this kind of equation was in fact at the Royal Military Academy at Woolwich in England in 1813, and was used for weapons research.
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