Open our JavaScript file and add the following box creation code to the page loaded event handler. Place the code after the createGround function:

// temporary function
function createBox() {
  var bodyDef = new b2BodyDef;
  var fixDef = new b2FixtureDef;

  bodyDef.type = b2Body.b2_dynamicBody;
  bodyDef.position.x = 50/pxPerMeter;
  bodyDef.position.y = 210/pxPerMeter;

  fixDef.shape = new b2PolygonShape();
  fixDef.shape.SetAsBox(20/pxPerMeter, 20/pxPerMeter);

  var body = carGame.world.CreateBody(bodyDef);
  body.CreateFixture(fixDef);

  return body;
}

We need to call our newly created createBox function. Place the following code after we call the createGround function inside initGame.

Now, we will test the physics world in a browser. You should see that a box is created at the given initial position. However, the box is not falling down; this is because we still have to...