       @nextState = 'rising'
       # Faster the run, higher the base jump, up to 33% improvement.
       kVelocity = (3 + Math.abs @velocity.x / @maxVelocity.x) / 4
-      @acceleration.set 0, @jumpAcceleration * kVelocity
-      @physics.drag.x = 2 * @_originalDrag.x
+      @acceleration.y = @jumpAcceleration * kVelocity
 
     _run: (direction) ->
       # Chain a start animation to the landing.

      @physics.collideWorldBounds = on

      @physics.drag.x = 1500
      @_originalDrag = @physics.drag.clone()

      h = @sprite.height
      w = @sprite.width

      if ending
        return unless @_jumpTimer.running
        @acceleration.y = @gravity.y
        @debug 'jump:end', @_jumpTimer.ms, { position: @physics.position }
        @_jumpTimer.stop()
        return
