# falloff(by:duration:) Creates an action that animates a change of a physics field’s falloff to a value relative to the existing value. ``` class func falloff(by falloff: Float, duration: TimeInterval) -> SKAction ``` ## Parameters `falloff` The value to add to the falloff. `duration` The duration of the animation, in seconds. ## Return Value A new action object. ## Discussion When the action executes, the field node’s [`falloff`](/documentation/SpriteKit/SKFieldNode/falloff) property animates from its current value to its new value. This action is reversible; the reverse is created as if the following code is executed: **Swift:** ```swift let action = SKAction.falloff(by: -falloff, duration: sec) ``` **Obj-C:** ```objc [SKAction falloffBy: -falloff duration: sec]; ``` --- Copyright © 2026 Apple Inc. All rights reserved. | [Terms of Use](https://www.apple.com/legal/internet-services/terms/site.html) | [Privacy Policy](https://www.apple.com/privacy/privacy-policy)