Rocket Thrust: Power Your Launch Into Space

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    Rocket Thrust
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Discussion Overview

The discussion revolves around the concept of rocket thrust and the reference frames used to analyze the motion of rockets, particularly focusing on the relationship between exhaust velocity and rocket speed. It includes theoretical considerations and mathematical reasoning related to the mechanics of rocket propulsion.

Discussion Character

  • Technical explanation, Mathematical reasoning, Debate/contested

Main Points Raised

  • Some participants assert that the reference frame of the rocket is the simplest choice for analysis, questioning the necessity of more complex frames.
  • There is confusion regarding the expression for exhaust velocity relative to the rocket, with one participant stating it should be "v" instead of "u" in the equation.
  • Another participant clarifies that the rocket's speed after expelling exhaust is represented as v + delta v, while the speed of the ejected material is defined as U, leading to a calculation of the difference as v + delta v - U.

Areas of Agreement / Disagreement

Participants express differing views on the correct formulation of exhaust velocity and the appropriate reference frame, indicating that multiple competing views remain without a clear consensus.

Contextual Notes

There are unresolved questions regarding the definitions and assumptions behind the variables used in the equations, as well as the implications of choosing different reference frames.

TkoT
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TL;DR
Confusion of thrust of a rocket
I saw the information of thrust of a rocket in the hyperphysics website, but I cant understand it.
1.why do the problem need to observe in two frame ( from an external framework and rocket frame of)?
2.why do the exhaust velocity relative to the rocket u=u+deltav-U?

Thank You
thrust of rocket2.png
 
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The reference frame of the rocket is the easiest one. You can always choose whatever reference frame you want but why make it harder than needed?
2.why do the exhaust velocity relative to the rocket u=u+deltav-U?
Where do you get that from? The exhaust velocity relative to the rocket is u which is not equal to u+deltav-U.
 
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mfb said:
The reference frame of the rocket is the easiest one. You can always choose whatever reference frame you want but why make it harder than needed?Where do you get that from? The exhaust velocity relative to the rocket is u which is not equal to u+deltav-U.
typo,why do the exhaust velocity relative to the rocket u=v+deltav-U? should be "v" not "u".
i get the information from this website: http://hyperphysics.phy-astr.gsu.edu/hbase/rocket.html#c1
thank u for your reply
 
The rocket speed after expelling the exhaust is v+delta v, the ejected material moves at U by definition. They just calculate the difference, which is v + delta v - U
 
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