SKSpriteNode slows down but shouldn't - ios

Question

I am trying to get my "word" to float across the screen; constant velocity, no impacts, no gravity, no friction. Everything works except the word slows down.
Code for creating word:
func createWordNode (word: String, atPos: CGPoint) -> SKSpriteNode {
let doneSize = CGSize(width: 50, height: 50)
let wordSprite = SKSpriteNode()
wordSprite.size = CGSize(width: doneSize.width * CGFloat(word.len()), height: doneSize.height)
wordSprite.position = atPos
wordSprite.blendMode = .replace
wordSprite.zPosition = zlvlBG + 1
let ltrs = Array(word.uppercased().characters)
for i in 0 ... ltrs.count - 1 {
let done = SKSpriteNode(imageNamed: "LetterTiles/Tile" + String(ltrs[i]) + ".png")
done.size = doneSize
done.position = CGPoint(x: doneSize.width * CGFloat(Double(i) - 1.5), y: 0)
done.blendMode = .replace
done.zPosition = zlvlBG + 1
wordSprite.addChild(done)
}
wordSprite.physicsBody?.restitution = 1
wordSprite.physicsBody?.friction = 0
wordSprite.physicsBody?.linearDamping = 0
wordSprite.physicsBody?.angularDamping = 0
wordSprite.physicsBody?.mass = 2000
wordSprite.physicsBody = SKPhysicsBody(rectangleOf: wordSprite.size)
wordSprite.physicsBody?.collisionBitMask = 0
wordSprite.physicsBody?.contactTestBitMask = 0
wordSprite.physicsBody?.categoryBitMask = categoryWords
wordSprite.physicsBody?.fieldBitMask = 0
wordSprite.physicsBody?.isDynamic = true
wordSprite.physicsBody?.affectedByGravity = false
wordSprite.physicsBody?.allowsRotation = false
var velocity = CGVector()
velocity.dx = 100
velocity.dy = 0
wordSprite.physicsBody?.velocity = velocity
wordSprite.physicsBody?.applyImpulse(velocity)
wordSprite.name = "Word:" + word
return wordSprite
}
I call function like:
addChild (createWordNode(word: "Done", atPos: CGPoint(x:-500, y:450)))
Any ideas why word slows down?
Thanks.

Answer 1

It looks like you are creating an object that doesn't need to be in the physics simulation. So you may want to reconsider simply dropping the physics related code and update the nodes position manually.
That being said if you wish this node to remain in the Physics simulation. You need to add the SKPhysicsBody to the SKSpriteNode before you start trying to modify properties. e.g.
wordSprite.physicsBody = SKPhysicsBody(rectangleOf: wordSprite.size)
wordSprite.physicsBody?.restitution = 1
wordSprite.physicsBody?.friction = 0
wordSprite.physicsBody?.linearDamping = 0
wordSprite.physicsBody?.angularDamping = 0
wordSprite.physicsBody?.mass = 2000

Answer 2

I worked with sprite a little bit. But, I am not an expert. Does it work for you to use an action instead of velocity as the following for example:
var moveRight = SKAction.moveTo(CGPointMake(400, 0), duration:2.0)
wordSprite.runAction(moveRight)
One thing to point out too. Why do you use applyImpulse. velocity should be enough. Did you try to remove it?