In my asteroids-style game I was looking for a way to limit the speed of the ship so that it didn't get too fast or outrun the missiles it fires. I call this with the update: method on the scene and it just checks the dx and dy values to make sure they are all inside the speed I want to set. In real code I would use a static or value loaded from…

SKPhyscisBody speed limiter

//  Speed limiter
- (void)shipSpeedLimit {
    
    //  Check the x velocity
    if (self.ship.physicsBody.velocity.dx > 500) {
        self.ship.physicsBody.velocity = CGVectorMake(500, self.ship.physicsBody.velocity.dy);
    } else if (self.ship.physicsBody.velocity.dx < -500) {
        self.ship.physicsBody.velocity = CGVectorMake(-500, self.ship.physicsBody.velocity.dy);
    }
    
    //  Check the y velocity
    if (self.ship.physicsBody.velocity.dy > 500) {
        self.ship.physicsBody.velocity = CGVectorMake(self.ship.physicsBody.velocity.dx, 500);
    } else if (self.ship.physicsBody.velocity.dy < -500) {
        self.ship.physicsBody.velocity = CGVectorMake(self.ship.physicsBody.velocity.dx, -500);
    }
}