Model Rocket- What does the 'v' in drag=kv^2 really mean?

AI Thread Summary
The discussion revolves around determining the correct value for 'v' in the drag equation used to predict the peak altitude of a model rocket. The user seeks clarification on whether 'v' should reflect the rocket's velocity considering gravity and air resistance or just the motor's output. It is clarified that the velocity should be the actual speed of the rocket relative to the surrounding air, as the motor provides force rather than velocity. The user acknowledges the complexity of incorporating drag into their calculations due to having two unknowns: the drag force and the actual velocity. Ultimately, the user decides to forgo including drag in their calculations for simplicity.
Andy24
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Hello! I am predicting the peak altitude of a model rocket based on some ground tests. I know that Total Force on the rocket=Thrust-mg-kv^2 but am stuck as to which value for 'v' to use? Is it the velocity of the rocket with the effects of gravity and air resistance taken into account or the velocity purely from the motor (without any air resistance or gravity taken into account)?

Your help is appreciated, thanks.
 
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The velocity at any given time is the rate of change of position over time, how fast the object is actually going. There is no such thing as "the velocity purely from the motor": the motor does not give a velocity, it gives a force. The velocity will be the result of all the forces acting on the object (and its previous velocity if it is already moving).
 
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DrClaude said:
That's reminds me that I forgot to add that it is the velocity with respect to the surrounding air.

Thanks for your response.. I understand now. I actually calculated the velocity based on some ground testing (where I found out the impulse of the motor) and was hoping to incorporate drag.. This may give you context: https://www.physicsforums.com/threads/coefficient-of-drag-on-a-model-rocket.871810/
Thanks for your help though, I think I might just leave incorporating drag into my calculations as I have 2 unknowns- the force due to drag as well as the actual velocity. Thanks again,
Andrea
 
Andy24 said:
Hello! I am predicting the peak altitude of a model rocket based on some ground tests. I know that Total Force on the rocket=Thrust-mg-kv^2 but am stuck as to which value for 'v' to use? Is it the velocity of the rocket with the effects of gravity and air resistance taken into account or the velocity purely from the motor (without any air resistance or gravity taken into account)?
In this context, the terms "drag" and "air resistance" are synonymous.
 

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