Calculating Coefficient of Air Resistance

[Bashyboy]

Hello,

For my Classical Mechanics Lab, my fellow students and I are to calculate the coefficient of air-resistance of several objects dropped from the roof of our science building. We are assuming that the air-resistance is linear in nature. The first method by which we calculate the drag coefficient is by measuring the diameters of the objects and their masses. The second method is to record the dropping of the objects and extrapolating data from the videos. Currently, I am working on the former method. We recorded the temperature on the day of the drop as 48 degrees Fahrenheit, with 85% humidity, and the pressure was 30.5 pounds/inch. I understand that the linear air-resistance coefficient is $b=\beta D$. I have searched the internet to find what beta is equal to, but all I can find is what is equal to at STP. Does anyone know of a formula for beta?

 

[SteamKing]

I don't know what a pressure of 30.5 pounds per inch means but it sounds pretty high, especially if it is supposed to be atmospheric. Are you sure your experiments aren't supposed to provide the data to calculate 'b'?

 

[PhanthomJay]

Barometic pressure 30.50 inches of mercury I guess, probably fine weather for an object drop. You probably can find an air density chart as a function of the given variables, which may not be much different from the standard air density usually given in slugs/ft^3 at 60 degrees F dry air at 29.95 inches barometric pressure. Not too much difference I would think. Also, I don't think it is a good assumption to use linear drag instead of quadratic drag.

 

[Bashyboy]

Yes, our experiment does provide us with the necessary data to calculate via the first method (that is, by using the video footage to extrapolate data). The second method of calculation is to use our diameter and mass measurements to get a "theoretical" value of b. Thus the reason for my wanting to know how to calculate beta.