title: Velocity units in SpriteKit
body: <p>I am using SpriteKit to shoot a projectile. The projectile node is given an impulse using <code>-(void)applyImpulse:(CGVector)impulse</code>. </p>
  
  <p>I want to calculate the distance the projectile will fly before hitting the ground, which can be done easily knowing the velocity vector of the projectile node's physicsbody and the gravitational acceleration (see <a href="http://en.wikipedia.org/wiki/Range_of_a_projectile">Wikipedia: Range of a Projectile</a>).</p>
  
  <p>It is however not clear what the units are of this distance and how they translate to distances in the <code>SKScene</code>. The <a href="https://developer.apple.com/library/ios/documentation/SpriteKit/Reference/SKPhysicsBody_Ref/Reference/Reference.html">documentation</a> of <code>SKPhysicsBody</code>'s velocity property do not mention units. I am currently running some tests to figure out the units and mapping to the SKScene. </p>
  
  <p>Has anyone figured this out already? </p>