# Aerodynamics of a ball/sphere

## Main Question or Discussion Point

I have to do an investigation about the Aerodynamics of a ball/sphere and I have to look at how changing the velocity and the cross-sectional area of the ball affects it's motion.

I'm planning to build a wind tunnel out of cardboard and put a fan in it to generate the velocity wanted...I've got sponge spheres but not entirely sure they are the most appropriate

Any advices to this investigation would be welcome! Thanks

What equations are involved in this?

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Mech_Engineer
Gold Member
Does your "investigation" have to be an experimental setup? The reason I ask is because you can pretty easily calculate the Reynold's number and drag coefficient of a sphere. By looking at how the ball's diameter and the stream's velocity are used in those calculations, you can see which parameters have the biggest effects on the ball's overall calculated drag. Heck you could even make some nice graphs that compare sphere diameter and wind speed as the independent variables to show exactly how they compare.

Building a home-made wind tunnel could be problematic as you would need to make sure the air stream flowing over the ball is uniform in velocity and hopefully not too turbulent... plus you would need a very sensitive force gauge to measure the drag on the sphere since the drag will probably be very, very small. It seems to me you would have to account for a lot more variables than if you just solved the problem analytically.

FredGarvin
Sponge is not going to be a good choice for a model material. The biggest thing is that the sponge will deflect and change shape as the flow increases thus introducing even more error into your set up. Make the model out of something solid with a smooth surface, unless you also want to look at surface roughness effects.

The other thing you need to look at is what data you will get from a wind tunnel. I say this because your original purpose is to study the effects on its motion. What data do you hope to get from the tunnel? How will you relate those things to a sphere's overall motion? You'll get some drag data, but how are you going to use that data?

Does your "investigation" have to be an experimental setup? The reason I ask is because you can pretty easily calculate the Reynold's number and drag coefficient of a sphere. By looking at how the ball's diameter and the stream's velocity are used in those calculations, you can see which parameters have the biggest effects on the ball's overall calculated drag. Heck you could even make some nice graphs that compare sphere diameter and wind speed as the independent variables to show exactly how they compare.

Building a home-made wind tunnel could be problematic as you would need to make sure the air stream flowing over the ball is uniform in velocity and hopefully not too turbulent... plus you would need a very sensitive force gauge to measure the drag on the sphere since the drag will probably be very, very small. It seems to me you would have to account for a lot more variables than if you just solved the problem analytically.
Yes it does have to be an experimental setup unfortunatelY!

Sponge is not going to be a good choice for a model material. The biggest thing is that the sponge will deflect and change shape as the flow increases thus introducing even more error into your set up. Make the model out of something solid with a smooth surface, unless you also want to look at surface roughness effects.

The other thing you need to look at is what data you will get from a wind tunnel. I say this because your original purpose is to study the effects on its motion. What data do you hope to get from the tunnel? How will you relate those things to a sphere's overall motion? You'll get some drag data, but how are you going to use that data?
Yeah maybe your right sponge is not so good...

"What data do you hope to get from the tunnel? How will you relate those things to a sphere's overall motion? You'll get some drag data, but how are you going to use that data?"

That is my problem since I'm not entirely sure how to get some data relevant to my investigation