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.. index:: Force Fields
************
Introduction
************
Force fields offer a way to influence a simulation, in example to add extra movement.
:doc:`Particles </physics/particles/index>`, :doc:`Soft Bodies </physics/soft_body/index>`,
:doc:`Rigid Bodies </physics/rigid_body/index>`, and :doc:`Cloth objects </physics/cloth/index>`
can all be affected by forces fields.
Force fields automatically affect everything.
To remove a simulation or particle system from their influence,
simply turn down the influence of that type of force field in its Field Weights panel.
- All types of objects and particles can generate fields,
but only curve object can bear a :doc:`/physics/forces/force_fields/types/curve_guide` field.
- Force fields can also be generated from particles.
See :doc:`Particle Physics </physics/particles/emitter/physics/index>`.
- The objects need to share at least one common layer to have an effect.
You may limit the effect on particles to a group of objects
(see the :doc:`Particle Physics </physics/particles/emitter/physics/index>` page).
Creating a Force Field
======================
.. reference::
:Mode: Object Mode
:Menu: :menuselection:`Add --> Force Field`
:Panel: :menuselection:`Physics --> Force Field`
To create a single force field,
you can select :menuselection:`Add --> Force Field` and select the desired force field.
This method creates an empty with the force field attached.
.. list-table:: Examples of an empty with the force field attached.
* - .. figure:: /images/physics_forces_force-fields_types_vortex_visualzation.png
Vortex force field.
- .. figure:: /images/physics_forces_force-fields_types_wind_visualzation.png
Wind force field.
- .. figure:: /images/physics_forces_force-fields_types_force_visualzation.png
Force force field.
To create a field from an existing object you have to select the object and
change to the *Physics* tab. Select the field type in the *Fields* menu.
.. note::
After changing the fields *Fields* panel or deflection *Collision* panel settings,
you have to recalculate the particle, soft body or cloth system by *Free Cache*,
this is not done automatically.
Particles react to all kinds of force fields,
soft bodies only to *Force*, *Wind*, *Vortex*
(they react on *Harmonic* fields but not in a useful way).
.. _force-field-common-settings:
Common Field Settings
=====================
Most fields have the same settings, even though they act very differently.
Settings unique to a field type are described below.
Curve Guide and Texture fields have very different options.
.. _bpy.types.FieldSettings.shape:
Shape
Sets the direction which is used to calculate the effector force.
For force fields from an empty object only *Point*, *Line* and *Plane* shapes are available,
as for a field from a 3D object there are additional *Surface* and *Every Point* options,
and *Curve* for a field from a curve.
:Point: Point with omni-directional influence. Uses the object origin as the effector point.
:Line:
The force only acts in the local XY plane, using the Z axis line as the effector.
:Plane:
The force only acts in the local Z direction, using the XY axis plane as the effector.
:Surface:
The force field acts on a 3D object's surface.
In this case, the Z axis is the surface normal.
:Every Point: Uses every vertex in the mesh object as an effector point.
.. _bpy.types.FieldSettings.strength:
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 the scene, keeping the same effects.
.. _bpy.types.FieldSettings.flow:
Flow
If nonzero, this adds a drag force proportional and opposite to the point velocity.
This effectively re-interprets the force field so that the *Strength* to *Flow* ratio
at a certain point defines the velocity of an "air flow" field, and objects are
encouraged to follow the flow by the resistance caused by the *Flow* drag force.
.. _bpy.types.FieldSettings.apply_to_location:
.. _bpy.types.FieldSettings.apply_to_rotation:
Affect
Location
Influence the location of particles and other physics entities.
Rotation
Influence the rotation of particles with :doc:`Dynamic Rotation </physics/particles/emitter/rotation>`.
The option is not relevant for other types of physics systems.
Disabling both options completely deactivates the force field.
.. _bpy.types.FieldSettings.noise:
Noise Amount
Adds noise to the strength of the force.
.. _bpy.types.FieldSettings.seed:
Seed
Changes the seed of the random noise.
.. _bpy.types.FieldSettings.use_absorption:
Absorption
Force gets absorbed by collision objects.
.. _bpy.types.FieldSettings.wind_factor:
Wind Factor
Specifies how much the force is reduced when acting parallel to a surface, e.g. cloth.
If set to 1, only the normal component of the force is taken into account.
Falloff
-------
Here you can specify the shape of the force field
(if the falloff *Power* is greater than 0).
.. _bpy.types.FieldSettings.falloff_type:
Shape
:Cone:
The falloff results in a cone-shaped force field. Additional options are the same as those of *Tube* options.
:Sphere:
The falloff is uniform in all directions, as in a sphere.
:Tube:
The falloff results in a tube-shaped force field.
The field's *Radial Power* can be adjusted,
as well as the *Minimum* and *Maximum* distances of the field.
.. _bpy.types.FieldSettings.z_direction:
Z Direction
The direction the force affects on the Z axis.
:+Z: The force only has an affect on the positive Z axis.
:-Z: The force only has an affect on the negative Z axis.
:Both Z: The force has an affect on the positive and negative Z axis.
.. _bpy.types.FieldSettings.falloff_power:
Power
How the power of the force field changes with the distance from the force field.
If *r* is the distance from the origin of the object, the force changes with 1/(*r* - *min* + 1)\ :sup:`power`.
A falloff of 2 changes the force field with 1/(*r* - *min* + 1)\ :sup:`2`,
which is similar to the falloff of gravitational pull.
.. _bpy.types.FieldSettings.use_min_distance:
.. _bpy.types.FieldSettings.distance_min:
Min Distance
The distance from the object's origin, up to where the force field is effective with full strength.
If you have a falloff of 0, this parameter will have no effect,
because the field is effective with full strength up to *Max Distance* (or infinite).
Shown by an additional circle around the object.
.. _bpy.types.FieldSettings.use_max_distance:
.. _bpy.types.FieldSettings.distance_max:
Max Distance
Specifies the maximum radius in which the force field affects other objects
(shown by an additional circle around the object).
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