The Physics of Wind (Not Aerodynamics in the strictest sense)

[freesonwang]

Hi there!

I'm doing research for computer science and I have to simulate wind movement. Obviously, I need to know stuff about wind movement.

I've tried several books and they haven't given me what I want. Most books have the whole "how do we make this airplane go fast" thing going on.

My project is more on "why does a flag wave in wind?", "why does hair wave in wind?", "why does a blade of grass move back and forth in wind?". I haven't been able to get any answers. (From my understanding, if you apply a force on something...it'll go that way Like if I push against a book, it'll move that way. Why does wind make something go back and forth?)

I like physics, but I'm not a big physics person, so go easy on me here if I'm missing something.

 

[russ_watters]

I'm not really clear on your question, but wind makes things move back and forth because of oscillations induced by lift.

 

[FredGarvin]

There's a couple of ways to look a this.

When an object is moved/deformed by a force, unless that force is great enough, the deflection will have a result of building up potential in the object that will want to make it return back to it's original position. Think of a spring or rubber band. The elastic potential energy is provided by the wind. When the object reaches it's maximum deflection, the potential to return itself to the original shape is highest. Once it gets back to that spot, the cycle starts all over again.

Of course all of the forces that cause the initial deflections are due to pressure imbalances and thus aerodynamic. If you want to get away from the aircraft angle on things, look into building modes of oscillation and things like shedding vorticies and Karaman vorticies. If you want to see something similar in an aircraft sense, do some research on flutter.

 

[nbo10]

Keywords: fluid dynamics and Navier-Stokes equations.

 

[FredGarvin]

Even though you are correct, Navier-Stokes for someone who is admittedly "not a big physics person" is going to have him running for the hills.