Type Method

# magneticField

Creates a field that attracts or repels objects based on their electrical charge, velocity, and distance from the field’s axis.

## Return Value

A physics field object. To use the field in a scene, attach it to the `physicsField` property of an `SCNNode` object.

## Discussion

Use this field type to make objects behave differently from one another when they enter a region, or to make an object's behavior different from its mass based behavior. A magnetic field behaves according to the second part of the Lorentz force equation modeling real-world electromagnetic forces—the field applies a force determined by the cross product of an object’s velocity vector and the magnetic field vector at the object’s location, with magnitude proportional to the object’s electric charge.

By default, physics bodies and particle systems have no electric charge, so they are unaffected by electric and magnetic fields. Use the `charge` property of a physics body or the `particleCharge` property of a particle system to add charge-based behavior.

When the field’s `strength` value is positive (the default), the magnetic field vectors circulate counterclockwise relative to the field’s `direction` vector. (That is, the magnetic field models a real-world magnetic field created by current in a wire oriented in the field’s direction.) To make field vectors circulate clockwise, set the field’s `strength` property to a negative value.

The default `falloffExponent` value for a magnetic field is `2.0`, indicating that the field’s effect diminishes with the square of distance from its center.

### Creating Physics Fields

`+ dragField`

Creates a field that slows any object in its area of effect with a force proportional to the object’s velocity.

`+ vortexField`

Creates a field whose forces circulate around an axis.

`+ radialGravityField`

Creates a field that accelerates objects toward its center.

`+ linearGravityField`

Creates a field that accelerates objects in a specific direction.

`+ noiseFieldWithSmoothness:animationSpeed:`

Creates a field that applies random forces to objects in its area of effect.

`+ turbulenceFieldWithSmoothness:animationSpeed:`

Creates a field that applies random forces to objects in its area of effect, with magnitudes proportional to those objects’ velocities.

`+ springField`

Creates a field that pulls objects toward its center with a spring-like force.

`+ electricField`

Creates a field that attracts or repels objects based on their electrical charge and on their distance from the field’s center.