title: Velocity meters per second or pixels per second?
body: <p>apple <a href="https://developer.apple.com/documentation/spritekit/skphysicsbody/1519635-velocity" rel="nofollow noreferrer">documentation</a> gives a physics bodies velocity as in meters per second.</p>
  
  <p>If this is true is there a relationship between pixels and meters? and if there is, what is it?</p>
  
  <p>or is this an error in the documentation and its really pixels per second?</p>