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Manual - Blender 2.34

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[edit] Force Fields

[edit] Description

Blender's physics system has a set of force fields that can influence a dynamic simulation (particles, hair, or soft bodies). Force fields will act upon points within a certain area, and influence their movement in various ways. Any object can be used as a force field, though Empties are the most common since they aren't rendered.

[edit] Options

Fields and Deflection panel.

All force fields have the same options (except Curve Guides, see the chapter on the static particles):

Strength

The strength of the field effect. This can be positive or negative to change the direction that the force operates in. A force field's strength is scaled with the force object's scale, allowing you to scale up and down scene, keeping the same effects.

Fall-off

How much the strength diminishes with distance from the force field object

Max distance indicator

Use MaxDist

Makes the force field only take effect within a specified maximum radius (shown by a dashed circle around the object)

MaxDist

The radius distance to affect points within

For all options for force fields, except MaxDist parameter, Ipo keys can be inserted. The Ipo curves (FStreng and FFall) are edited as Object Ipo types in the Ipo window. See the chapter on the Animation Basics for more on Animation and IPO.

Force fields come in a few different types:

[edit] Spherical

Spherical field indicator

Gives a constant force towards (positive strength) or away from (negative strength) the object's center. This acts like gravity, sucking points towards the object, or repelling them away.

Spherical force fields are much faster to calculate than mesh-based deflection, and in cases where accuracy isn't of prime importance, they can be used with MaxDist and a negative strength for a much faster alternative for collisions.

[edit] Vortex

Vortex field indicator

Vortex fields give a spiralling force that twists the direction of points around the force object's local Z axis. This can be useful for making a swirling sink, or tornado, or kinks in particle hair.

[edit] Wind

Wind field indicator

Wind gives a constant force in a single direction, along the force object's local Z axis. The strength of the force is visualised by the spacing of the circles shown

[edit] Hints

In trying to debug why the wind isn't blowing, check:

• Is the Wind Empty on the same Layer as the Particle Emitter?
• Do you have MaxDist on for the Wind but not a high enough distance value?
• Are your Wind circles pointing in the right direction?

[edit] Deflection

[edit] Description

As well as force objects, any mesh object can be set as a deflector. Particles will then bounce on the surface of the mesh. You can control how much the particles bounce with the Damping value, add some randomness to the bounce with Rnd Damping, and you can define the percentage of particles which pass through the mesh with the Permeability parameter.

You will not see any extra graphic indicators with deflectors as you do with force fields.

[edit] Options

Fields and Deflection panel.

Deflectors have two sets of options, for particle deflection and softbody deflection:

[edit] Particles

Damping

The amount of bounce that surfaces will have, ranging from:

• 0.0 - No damping, particles will have maximum bounce, to
• 1.0 - Maximum damping, particles will not bounce at all

Rnd Damping

Adds a random variability to the bounce. For example, with a Damping of 1.0 and a Rnd Damping of 0.5, the damping will vary between 1.0 and 1.5.

Permeability

Percentage of particles passing through the mesh, ranging from:

• 0.0 - No particles pass through, to
• 1.0 - All particles pass through the deflector

[edit] Soft Body

Damping

The amount of bounce that surfaces will have, ranging from:

• 0.0 - No damping, soft bodies will have maximum bounce, to
• 1.0 - Maximum damping, soft bodies will not bounce at all.

Inner / Outer

An artificial padding distance added to the inside and outside of each face, to help prevent intersections

If you set up a particle deflector you'll have to make sure sufficient keys are available for Blender to calculate the collisions with sufficent detail. If you see particles moving through your deflector or bouncing in the wrong positions, then there might be problem with too few keys (Keys setting, Particle Motion tab) or your particle/deflector is moving too fast.

For the options from the Particles group, Ipo keys can be inserted. The Ipo curves (Damping, RDamp and Perm) are edited as Object Ipo types in the Ipo window. See the chapter on the Animation Basics for more on Animation and IPO.

[edit] Examples

Here is a Meta object, dupliverted to a particle system emitting downwards, and deflected by a mesh cube:

Modified end result.

[edit] Hints

• Make sure that the normals of the mesh surface are facing towards the particles/points for correct deflection.
• You can animate moving deflectors but particles can leak through the mesh if the deflector moves to fast or if the mesh is complicated. This can be partly solved by increasing the Keys parameter for the particle emitter.
• After changing any parameters, you will need to select your particle emitter and go back to the Particles tab and press RecalcAll button.
• More keys means longer calculation times and usage of more memory. See the section called Particles for how to set up particle emitters.

[edit] Limitations & Work-Arounds

Currently (in Blender 2.42) static particles ignore mesh deflectors.

Manual

Redirects to fix

• Manual/Animation Basics → Doc:Manual/Animation/Basics
• Manual/Particles → Doc:Manual/Physics/Particles
• Manual/Rigid Bodies → Doc:Manual/Physics/Rigid Bodies
• Manual/Soft Bodies → Doc:Manual/Physics/Soft Bodies
• Manual/Static Particles (Hair) → Manual/Static Particles