Force, impulse, and linear velocity

Let's jump straight to the point with some new lines in the Main function:

public function Main() {
  world=new b2World(new b2Vec2(0,10),true);
  debugDraw();
  floor();
  sphereVector=new Vector.<b2Body>();
  for (var i:int=0; i<3; i++) {
    sphereVector.push(sphere(170+i*150,410,40));
  }
  var force:b2Vec2=new b2Vec2(0,-15);
  var sphereCenter:b2Vec2=sphereVector[0].GetWorldCenter();
  sphereVector[0].ApplyForce(force,sphereCenter);
  sphereCenter=sphereVector[1].GetWorldCenter();
  sphereVector[1].ApplyImpulse(force,sphereCenter);
  sphereVector[2].SetLinearVelocity(force);
  addEventListener(Event.ENTER_FRAME,updateWorld);
}

This is the core of this chapter and it's a lot of new stuff, so let's look at it line by line:

var force:b2Vec2=new ...

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