 scene.physicsWorld.gravity = CGVector(dx: 0, dy: 0)
 scene.physicsBody = SKPhysicsBody(edgeLoopFromRect: scene.frame)
 sceneView.showsFPS = true
+sceneView.showsPhysics = true
 sceneView.presentScene(scene)
 
 XCPlaygroundPage.currentPage.liveView = sceneView

            SKAction.waitForDuration(0.1)
            ]),
        count: 100))
}
    sand.physicsBody = SKPhysicsBody(circleOfRadius: sand.size.width/2)
    sand.name = "sand"
    scene.addChild(sand)
    sand.physicsBody!.restitution = 1.0
    sand.physicsBody!.density = 20.0
}

func shake() {
    scene.enumerateChildNodesWithName("sand") { node, _ in
        node.physicsBody!.applyImpulse(CGVector(dx: 0, dy: random(min: 20, max: 40)))
    }
}

delay(seconds: 2.0) {
