code: function (/* dt */) {
              // update the velocity
              this.computeVelocity(this.vel);
  
              // update the body ancestor position
              this.ancestor.pos.add(this.vel);
  
              // returns true if vel is different from 0
              return (this.vel.x !== 0 || this.vel.y !== 0);
          }
docs: Updates the parent's position as well as computes the new body's velocity based
  on the values of force/friction/gravity.  Velocity chages are proportional to the
  me.timer.tick value (which can be used to scale velocities).  The approach to moving the
  parent Entity is to compute new values of the Body.vel property then add them to
  the parent.pos value thus changing the postion the amount of Body.vel each time the
  update call is made. <br>
  Updates to Body.vel are bounded by maxVel (which defaults to viewport size if not set) <br>
  
  In addition, when the gravity calcuation is made, if the Body.vel.y > 0 then the Body.falling
  property is set to true and Body.jumping is set to !Body.falling.
  
  At this time a call to Body.Update does not call the onBodyUpdate callback that is listed in the init: function.
  @name update
  @memberOf me.Body
  @function
  @return {boolean} true if resulting velocity is different than 0
  @see source code for me.Body.computeVelocity (private member)