Introduction

Force fields offer a way to influence a simulation, in example to add extra movement. Particles, Soft Bodies, Rigid Bodies, and Cloth objects 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 Curve Guide field.

• Force fields can also be generated from particles. See Particle Physics.

• 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 Particle Physics page).

Creating a Force Field

Reference

Mode:

Object Mode

Menu:

Add ‣ Force Field

Panel:

Physics ‣ Force Field

To create a single force field, you can select Add ‣ Force Field and select the desired force field. This method creates an empty with the force field attached.

Examples of an empty with the force field attached.

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).

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.

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.

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.

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.

Affect

• Location

  Influence the location of particles and other physics entities.

  Rotation

  Influence the rotation of particles with Dynamic Rotation. The option is not relevant for other types of physics systems.

Disabling both options completely deactivates the force field.

Noise Amount

Adds noise to the strength of the force.

Seed

Changes the seed of the random noise.

Absorption

Force gets absorbed by collision objects.

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).

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.

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.

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)power. A falloff of 2 changes the force field with 1/(r - min + 1)2, which is similar to the falloff of gravitational pull.

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.

Max Distance

Specifies the maximum radius in which the force field affects other objects (shown by an additional circle around the object).