Understanding Cofficient of Drag

Main Question or Discussion Point

Ok so i have looked and looked for a simple way to under stand how to find drag using the coefficient of drag.

the formula i found is off of NASA website and it reads

Drag = Coefficient * [ (Density * Velocity ^2)* .5 ] * reference area

here is my question
what units do i use.
When i set it up with these numbers
CD = 0.31 (unitless i know)
Ref Area = 8 sq ft (ruff guess)
Velocity = 75 fps
density = 24 in Hg

I end up with 167,400. but i know no clue as to what unit that is? should i be putting every thing in with different units... what is the end units?
 

Answers and Replies

2,903
13
I would do dimensional analysis.
 
At the risk of sounding like a moron..... HUH?
 
Andy Resnick
Science Advisor
Education Advisor
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1,718
Can you post a link to the site? Doing a quick dimensional analysis gives a consistent result:

[drag] = ML/T^2 (force, M = mass, L = length, T = time)

but you have odd units of density: pressure? It should be M/L^3
 
http://www.grc.nasa.gov/WWW/K-12/airplane/drageq.html" [Broken]
 
Last edited by a moderator:
2,903
13
Please google dimensional analysis.


Hint: You can find this also in any chemistry book.
 

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