The abstract superclass for objects that connect physics bodies.
- iOS 7.0+
- macOS 10.9+
- tvOS 9.0+
- watchOS 3.0+
SKPhysics object connects two physics bodies so that they are simulated together by the physics world. You never instantiate objects of this class directly; instead, you instantiate one of the subclasses that defines the kind of joint you want to make.