[...]
	gravity := box2d.MakeB2Vec2(0.0, -10.0)
	b2World := box2d.MakeB2World(gravity)

	var body1 *box2d.B2Body
	var body2 *box2d.B2Body
	var body3 *box2d.B2Body
	{
		// Body 1
		bd := box2d.MakeB2BodyDef()
		bd.Position.Set(5, 4)
		bd.Type = box2d.B2BodyType.B2_staticBody
		body1 = b2World.CreateBody(&bd)
		shape := box2d.MakeB2CircleShape()
		shape.M_radius = 0.5
		fd := box2d.MakeB2FixtureDef()
		fd.Shape = &shape
		fd.Density = 10.0
		body1.CreateFixtureFromDef(&fd)
	}

	{
		// Body 2
		bd := box2d.MakeB2BodyDef()
		bd.Position.Set(5, 6)
		bd.Type = box2d.B2BodyType.B2_dynamicBody
		bd.FixedRotation = true
		body2 = b2World.CreateBody(&bd)
		shape := box2d.MakeB2CircleShape()
		shape.M_radius = 0.5
		fd := box2d.MakeB2FixtureDef()
		fd.Shape = &shape
		fd.Density = 10.0
		body2.CreateFixtureFromDef(&fd)
	}
	{
		// weld joint
		w := box2d.MakeB2WeldJointDef()
		w.BodyA = body1
		w.BodyA.SetFixedRotation(false)
		w.BodyB = body2
		w.BodyB.SetFixedRotation(false)
		w.LocalAnchorA = box2d.MakeB2Vec2(0, 2)
		w.LocalAnchorB = box2d.MakeB2Vec2(0, 0)
		w.FrequencyHz = 4.0
		w.DampingRatio = 0.5
		b2World.CreateJoint(&w)
	}

	{
		bd := box2d.MakeB2BodyDef()
		bd.Position.Set(5.4, 9.0)
		bd.Type = box2d.B2BodyType.B2_dynamicBody
		body3 = b2World.CreateBody(&bd)
		shape := box2d.MakeB2CircleShape()
		shape.M_radius = 0.5
		fd := box2d.MakeB2FixtureDef()
		fd.Shape = &shape
		fd.Density = 10
		body3.CreateFixtureFromDef(&fd)
	}
[...]

b2World.Step(1/60.0, 8, 3)