Drag Coefficient out by a factor of 10, can anyone help?

[Euan2007]

Drag Coefficient out by a factor of 10, can anyone help??

Im doing an experiment on the drag of a sphere and am trying to work out the drag coefficient. From looking at data online this should be around 0.5 (its a smooth sphere). Using a wind tunnel I measured the drag for various sizes of spheres and wind speeds. An example of one of my results is

Drag - 0.68N
Wind Speed - 7.8m/s
Radius of Sphere - 0.0371m

Then, using the formula

Drag Coefficent = (2 x Drag) / Area x Wind Speed^2 x Density of Air

Having measured the room temperature to be 22 degrees celcius I took the density of air to be 1.204kg/m^3 and the projected frontal area was calculated using pi x r^2

But this equals 5.039! so could anyone point out where I am going wrong?? I am 90% sure all of my values are correct. Thanks in advance for any help :)

 

[Weirdbro]

Are you absolutely sure about the calculated drag force? Your equation is correct, although I get 4.293 when I plug your data into it (probably rounding differences). I'm not terribly familiar with wind tunnels, but try checking the units of the readings that you're getting from it.

 

[astrokreng]

I would suggest double-checking your calculations and making sure that all of your units are consistent. It is also possible that there may be some error in your measurements or experimental setup that is causing the discrepancy in your results. I would recommend consulting with a colleague or mentor to review your data and calculations and see if they can identify any potential sources of error. Additionally, you may want to consider conducting multiple trials to ensure the accuracy and reproducibility of your results. Good luck with your experiment!