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# updateCollisionPairs()

Forces the physics engine to reevaluate possible collisions between physics bodies.

```
func updateCollisionPairs()
```

## Discussion

By default, SceneKit checks for collisions between physics bodies only once per simulation step. If you directly change the positions of any physics bodies outside of a [`SCNPhysicsContactDelegate`](/documentation/SceneKit/SCNPhysicsContactDelegate) method, call the [`updateCollisionPairs()`](/documentation/SceneKit/SCNPhysicsWorld/updateCollisionPairs()) method before using any of the methods listed in Searching for Physics Bodies Detecting Contacts Between Physics Bodies.

## See Also

[`contactDelegate`](/documentation/SceneKit/SCNPhysicsWorld/contactDelegate)

A delegate that is called when two physics bodies come in contact with each other.


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