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

  • #1
6
0
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.
 

Answers and Replies

  • #2
DrClaude
Mentor
7,758
4,268
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).
 
  • #5
6
0
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
 
  • #6
21,951
4,996
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.
 

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

  • Last Post
Replies
8
Views
3K
Replies
9
Views
9K
  • Last Post
Replies
4
Views
203
  • Last Post
Replies
0
Views
4K
Replies
6
Views
8K
Replies
5
Views
2K
Replies
7
Views
3K
Replies
4
Views
2K
Replies
6
Views
5K
  • Last Post
Replies
3
Views
3K
Top