Swift + Playground physics

physics.swift

import SpriteKit
import XCPlayground

let width:CGFloat = 400
let height:CGFloat = 400
let canvasWidth: UInt32 = UInt32(width)
let canvasHeight: UInt32 = UInt32(height)

let view:SKView = SKView(frame:CGRectMake(0, 0, width, height))
let scene:SKScene = SKScene(size:CGSizeMake(width, height))
scene.backgroundColor = SKColor.blackColor()
view.presentScene(scene)

scene.physicsWorld.gravity = CGVectorMake(0, -1)

for var i = 0; i < 100; i++ {
    let radius:CGFloat = 6
    let shape = SKShapeNode(circleOfRadius:radius)
    shape.fillColor = SKColor.blueColor()
    shape.position = CGPoint(
        x: CGFloat(arc4random_uniform(canvasWidth)),
        y: CGFloat(arc4random_uniform(canvasHeight)))
    scene.addChild(shape)
    
    shape.physicsBody = SKPhysicsBody(circleOfRadius:radius)
    shape.physicsBody.friction = 0.01
    shape.physicsBody.restitution = 0.99
    shape.physicsBody.mass = 1.0
}

scene.physicsBody = SKPhysicsBody(
    edgeLoopFromRect:CGRect(x:0, y:0, width:width, height:height))

XCPShowView("my view", view)

Thanks!!