A bit of a physics question

[jr1104]

Probably not the best place to put this, but I figured someone might know.

I'm trying to calculate the change in density in different parts of the International Standard Atmosphere. The formula I'm using works fine for the troposphere, where the lapse rate is negative, but when it gets to the stratosphere, it all goes weird, due to the positive lapse rate. I'm wondering if anyone knew what I'm supposed to do here, or if there is a different equation to use?

Thanks

 

[jr1104]

d/d0=(t/t0)^((g/LR)-1) where d is density, t is temp and L is the lapse rate.

I'm trying it a slightly different way now, by working out temperature and pressure, then using d = P/Rt, but I still have the same problem with the positive lapse rate not working in my equations.

 

[jr1104]

Well, I have the formulas, and I'm wanting to calculate the density at different heights, in order to use it to calculate aerodynamic drag. But because the object is passing through different layers of the atmosphere, I need to use different base temperature and lapse rate values. The problem is that when calculating the pressure, using formula 1 below, the positive lapse rate means that the pressure increases, which obviously it shouldn't do if I am gaining altitude.

formula 1: P/P(0) = T/T(0) ^ (g/LR)

I've got around this for now by entering the lapse rate as negative all the time, and this gives me the graph I expected, but it seems like that isn't the correct thing to do.