Another SpriteKit starter, some examples of how to use physics and actions

Box.swift

import Foundation
import SpriteKit

func getColorName(_ color: NSColor) -> String {
    switch color {
    case .black: return "black"
    case .white: return "white"
    case .gray: return "gray"
    case .red: return "red"
    case .green: return "green"
    case .blue: return "blue"
    case .cyan: return "cyan"
    case .magenta: return "magenta"
    case .yellow: return "yellow"
    default: return "Exotic"
    }
}

func getRandomColor() -> NSColor {
    return [
        NSColor.black, NSColor.white, NSColor.gray, NSColor.red, NSColor.green,
        NSColor.blue, NSColor.cyan, NSColor.magenta, NSColor.yellow
    ].randomElement()!
}

class Box {
    static var spinForward = SKAction.rotate(byAngle: 2 * CGFloat.pi, duration: 1.0)
    static var spinBackward = SKAction.rotate(byAngle: 2 * CGFloat.pi, duration: 1.0).reversed()

    let pBody: SKPhysicsBody
    let sprite: SKShapeNode
    var spinningForward = false

    var position: CGPoint {
        get { return sprite.position }
        set { sprite.position = newValue }
    }

    init(dimensions: CGSize, color: SKColor) {
        self.sprite = SKShapeNode(rectOf: dimensions)
        self.sprite.fillColor = color
        self.sprite.strokeColor = color

        self.pBody = SKPhysicsBody(rectangleOf: dimensions)

        self.pBody.isDynamic = true
        self.pBody.categoryBitMask = 1
        self.pBody.collisionBitMask = 1
        self.pBody.contactTestBitMask = 1
        self.pBody.restitution = 1.0

        self.sprite.physicsBody = self.pBody
        self.sprite.userData = ["Box" : self]

        self.spinningForward = true
        self.sprite.run(SKAction.repeatForever(Box.spinForward))

        self.flySomewhere()
    }

    func addToScene(_ scene: SKScene) {
        scene.addChild(self.sprite)
    }

    func contact() {
        if self.spinningForward {
            self.sprite.run(SKAction.repeatForever(Box.spinBackward))
        } else {
            self.sprite.run(SKAction.repeatForever(Box.spinForward))
        }

        self.spinningForward = !self.spinningForward

        flySomewhere()
    }

    func contact(by: Box) {
        let hisPosition = by.sprite.position
        let hisColor = by.sprite.fillColor
        let hisSize = by.sprite.frame.size

        self.sprite.removeAllActions()
        self.sprite.removeAllChildren()

        contact()

        let px = Int(hisPosition.x)
        let py = Int(hisPosition.y)
        let sw = Int(hisSize.width)
        let sh = Int(hisSize.height)

        let pt = "\(px), \(py)"
        let ct = getColorName(hisColor)
        let st = "\(sw), \(sh)"
        let positionLabel = SKLabelNode(text: pt)
        let colorLabel = SKLabelNode(text: ct)
        let sizeLabel = SKLabelNode(text: st)

        positionLabel.position = CGPoint(x: 0, y: self.sprite.frame.size.height / 4.0)
        setLabelDefaults(positionLabel)

        colorLabel.position = CGPoint(x: 0, y: 0)
        setLabelDefaults(colorLabel)

        sizeLabel.position = CGPoint(x: 0, y: -self.sprite.frame.size.height / 4.0)
        setLabelDefaults(sizeLabel)

        self.sprite.addChild(positionLabel)
        self.sprite.addChild(colorLabel)
        self.sprite.addChild(sizeLabel)

        self.sprite.fillColor = getRandomColor()
        self.sprite.setScale(CGFloat.random(in: 0.5...1.5))
    }

    func flySomewhere() {
        let randomImpulseX = CGFloat.random(in: -500...500)
        let randomImpulseY = CGFloat.random(in: -500...500)
        self.pBody.velocity = CGVector(dx: randomImpulseX, dy: randomImpulseY)
    }

    func setLabelDefaults(_ label: SKLabelNode) {
        label.fontSize *= 0.75
        label.color = .black
        label.colorBlendFactor = 1.0
        label.fontName = "Courier New"
    }
}

class Contact: NSObject, SKPhysicsContactDelegate {
    func didBegin(_ contact: SKPhysicsContact) {
        let bodyA = contact.bodyA
        let bodyB = contact.bodyB

        guard let spriteA = bodyA.node else { return }
        guard let spriteB = bodyB.node else { return }

        if let boxA = spriteA.userData?["Box"] as? Box {
            if let boxB = spriteB.userData?["Box"] as? Box {
                boxA.contact(by: boxB)
                boxB.contact(by: boxA)
            } else {
                boxA.contact()
            }
        } else {
            if let boxB = spriteB.userData?["Box"] as? Box {
                boxB.contact()
            }
        }
    }
}

GameScene.swift

import SpriteKit
import GameplayKit

class GameScene: SKScene {

    var box1: Box!
    var box2: Box!
    var contact: SKPhysicsContactDelegate!

    override func didMove(to view: SKView) {
        self.contact = Contact()

        let b1 = Box(dimensions: CGSize(width: 200, height: 200), color: .green)
        let b2 = Box(dimensions: CGSize(width: 200, height: 200), color: .blue)

        b1.position = CGPoint(x: 0.0, y: 200.0)
        b2.position = CGPoint(x: 0.0, y: -200.0)

        self.box1 = b1
        self.box2 = b2

        let scene = self

        b1.addToScene(scene)
        b2.addToScene(scene)

        scene.physicsWorld.gravity = CGVector(dx: 0, dy: 0)
        scene.physicsWorld.contactDelegate = contact

        let boundary = SKPhysicsBody(edgeLoopFrom: scene.frame)

        let boundaryNode = SKNode()
        boundaryNode.physicsBody = boundary

        scene.addChild(boundaryNode)
    }
}