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How to simulate gravity in a SpriteKit scene

Paul Hudson       @twostraws

Once you’ve given all your SpriteKit nodes physics bodies, you might want to add some simulated gravity so they fall to the ground over time. This technique is also useful if you want to simulate wind (think of it like horizontal gravity), or even for making the user tilt their device to make nodes fall in different directions.

Gravity for your scene is configured using the physicsWorld.gravity property. By default it’s set to a value equal to Earth’s gravity of 9.8 meters per second, but you can change that however you want. For example, you might want to simulate someone walking on the moon where gravity is 1.62 meters per second:

physicsWorld.gravity = CGVector(dx: 0, dy: -1.62)

Alternatively you can disable gravity entirely by using a zero vector:

physicsWorld.gravity = .zero

These changes don’t need to be permanent – you could disable gravity when the player picks up an anti-grav belt, then re-enable it after 30 seconds.

Available from iOS 8.0 – learn more in my book Dive Into SpriteKit

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