Re: Calculating Drag
Hi Ben,
I looked on the internet for about 2 hours and couldn't find a thing.
I guess I should of been more specific. I am dealing with the speed
of bullets. So we are definetly talking about over the speed of sound.
But then again in flight they slow down to below the speed of sound.
But I don't believe I will be dealing with them when they get to that
point. What does k stand for? Would that be the coeficient of the bullet?
F is the negative force on the bullet right? Over the speed of sound
does the bullet slow down at vx/vx^3 or something like that? God
wish I had of stayed in college and finished physics now. Know any
good web sites? I apreciate your help.
roachd_7 at yahoo.com
----- Original Message -----
From: Ben Logan <wbljr79 at HOTMAIL.COM>
To: <EUPHORIA at LISTSERV.MUOHIO.EDU>
Sent: Tuesday, February 08, 2000 3:12 AM
Subject: Re: Calculating Drag
> Hi, David.
>
> I'm not sure whether or not you need to know the viscosity of air, but
maybe
> these relations will help:
>
> For low speeds where laminar flow occurs:
> f = kv, that is, the force of air resistance is roughly
proportional
> to the speed.
>
> For speeds above laminar flow, but below supersonic speeds:
> f = k(v^2), that is, the force of air resistance is roughly
> proportional to the square of the speed.
>
> As v approaches the speed of sound:
> f = k(v^3), that is, the force of air resistance is (very) roughly
> proportional to the cube of the speed.
>
> In the above proportions, k is the constant of proportionality and varies
> for each body. I assume that it also depends on such things as air
> temperature (which would be a factor in determining viscosity, I would
> think), humidity, atmospheric pressure, etc.
>
> If I was going to use the above to calculate the position of a projectile,
> I'd probably use f=k(v^2) unless the projectile broke the sound barrier.
As
> I understand it, laminar flow occurs only at very low speeds and probably
> wouldn't be worth considering.
>
> Having said that and then trying to derive the equations which describe
the
> components of velocity of a projectile, the equations are much simpler for
> f=kv. (Assuming I've done everything right!)
>
> v_x = vcos(theta)/(1-(kt/m))
> v_y = (vsin(theta)-gt)/(1+(kt/m))
> where, v_x is the x-component of velocity, v_y is the y-component, v is
> the initial velocity, and theta is the angle of projection.
>
> As for f=kv^2, if I did everything correctly, you should be able to solve
> the following two equations for v_x and v_y to obtain the appropriate
> equations. I've run out of time, but I'll try later.
>
> v_x = k*v_x*t*sqrt((v_x)^2+(v_y)^2)/m + vcos(theta)
> v_y = -k*v_y*t*sqrt((v_x)^2+(v_y)^2)/m - gt + vsin(theta)
>
> (m is the mass of the projectile)
>
> I hope this helps,
>
> Ben
>
> >From: David Roach <roachd_76 at YAHOO.COM>
> >Reply-To: Euphoria Programming for MS-DOS <EUPHORIA at LISTSERV.MUOHIO.EDU>
> >To: EUPHORIA at LISTSERV.MUOHIO.EDU
> >Subject: Calculating Drag
> >Date: Tue, 8 Feb 2000 04:40:19 -0500
> >
> >Hello All,
> >
> >Does any one know how to calculate drag for a projectile.
> >I know there is coeficiant and the viscosity of air. I think?
> >Any equation that go along with this. Any help would be great.
> >
> >roachd_76
>
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