Deformers let you influence particle positions in a variety of ways.

To deform particles

1. Create a scene with particles.
2. Select the particle object.
3. In the Animation menu set, click Create Deformers.
4. Select the deformer you want to use on the selected particle object. You can deform particles with all deformers except for the skinning and blend shapes deformers.

   The deformers operate in the same way as they do for geometry. You can also layer deformers.

You can also combine particle deformation with forces: deform the particles, then apply the desired forces to the intermediate object. Alternatively, you could apply forces to particles before the application of a deformer.