import UIKit

// create a 'scene' with a red square
let view = UIView(frame: CGRectMake(0, 0, 300, 100))
let subView = UIView(frame: CGRectMake(0,0,50,50))
subView.backgroundColor = UIColor.redColor()
view.addSubview(subView)

// add gravity
let animator = UIDynamicAnimator(referenceView: view)
let gravity = UIGravityBehavior(items: [subView])
animator.addBehavior(gravity)
