Hair-Force tutorial. This tutorial will help you blow away your lawn.

Heavy pages coming up!

Follow up:

This tutorial is specifically about grass with Hair and particle Forces.
I will not get into the Grass itself as there is a specific tutorial about that in the Hair section of this site. Grass & Flowers with Hair
What we want to make here is a wind flowing over a field of grass.
In the next pages I'll also show what other forces you can apply to tho Hair.

First of all we will start with a plane or a circle or a landscape object to apply the Hair on.
I've tested two main setups with completely different results.
The first setup is with Hair as it is, the second is with Hair with a reversed gravity (9.81, without the minus), the second setup is nice straight grass. And the first (which I like a lot) is more like wet and messy grass.

I've also tested some setups with two Hair objects, the second Hair is much higher and sparser.

As a general remark I would like to say that this whole setup took quite a long time to get done right.
There is a lot of fiddling the parameters to get approximately what you want.

What I basically did is to add several Wind objects (classic Particle forces)

The wind objects I used here have a force of 60 an unlimited size and I enabled the Falloff (this is important) and set its size as to have the wind objects intersect each-other .

Next step (for animation) is to randomize the wind a bit. I added a Vibrate tag to each wind. The Vibrate is set to rotate 180 degrees with a low frequency of 0.4. or lower.
To finalize the randomization I grouped all the Wind objects in one Null and added another Vibrate tag on that group.
Have a test run (play) to see the result. (fewer guides make a faster preview)

The first movie has a normal gravity (-9.81) the second one has the reversed gravity (9.81 upwards)

This is only one way of doing the trick. You could also move the Wind objects on specific paths as to get a better control over them.

On the next pages I'll show some results I got with different setups and different forces.

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