Beginner: How do i make force field affect only a certain area of hair

Question

I'm trying to make a force field in which only a segment of the plane of hair is affected. However, the force field i created is non location dependent - where ever i placed the force field, all the hair particles are still affected. Is there a way to make the effects of the force field local?

Example:

I only want hair particles that is in front of the forcefield to be affected instead of the whole plane.

Answer 1

Hair Dynamics is a feature that enables for the whole particle system no matter what but you can tweak which forces affect to the system.

So I think the only solution is to make two Particle Systems: one affected by the Force Field and another one that it's not. These are the steps:

1. Create two equal Particle Systems for your plane. They might have Hair Dynamics enabled for working with Force Fields.
2. Create a Vertex Group for the area you don't want to be affected by your Force Field. (Eventualy, you might need more vertices on your plane to paint a proper Vertex Group).
3. On the first System, go to Vertex Group and add that Vertex Group into the Density field.
4. On the second one, add the Vertex Group too but check the double-arrow icon on the left.
5. Now, you might need to tweak the number of hair on the two Systems to have the desired density.
6. Go back to the first System and, on the Field Weights area, set to 0 the Fields you want to avoid -depending on your Field Force.

Now you might have a result like this, where the center area is not being affected by a Wind Force Field.Note that in this case I could just disabled Hair Dynamics for the first System.

Answer 2

You can do it using multiple hair particle systems and vertex groups.

First you need to make 2 vertex groups in your mesh (one for affected by force fields particles, other for not affected)

Just select vertexes for group click + sign in Data tab and click assign each of them individually.

When you have 2 vertex groups, add 2 particle systems and customize them how you want.

For the first one, in vertex groups part set density to the first group you have created:

In other particle system set density to the second vertex group.

When go to field weights in the particle system (that should not be affected by them). And put force field you are going to use weight to 0. (Wind for example)

When add Force field:

And now effects of force field will only affect particle system that does not have it's weight set to 0.