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# strength(to:duration:)

Creates an action that animates a change of a physics field’s strength.

```
class func strength(to strength: Float, duration: TimeInterval) -> SKAction
```

## Parameters

`strength`

The new strength for the field.

`duration`

The duration of the animation.

## Return Value

A new action object.

## Discussion

When the action executes, the field node’s [`strength`](/documentation/SpriteKit/SKFieldNode/strength) property animates from its current value to its new value.

This action is not reversible; the reverse of this action has the same duration but does not do anything.

---

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