function createGround(x, y, width, height, rotation) {
  var bodyDef = new b2BodyDef;
  var fixDef = new b2FixtureDef;

  bodyDef.type = b2Body.b2_staticBody;
  bodyDef.position.x = x /pxPerMeter;
  bodyDef.position.y = y /pxPerMeter;
  bodyDef.angle = rotation * Math.PI / 180;

  fixDef.shape = new b2PolygonShape();
  fixDef.shape.SetAsBox(width/pxPerMeter, height/pxPerMeter);
  fixDef.restitution = 0.4;
  fixDef.friction = 3.5;

  // create the body from the definition.
  var body = carGame.world.CreateBody(bodyDef);
  body.CreateFixture(fixDef);

  return body;
}