Box2d中的摩擦不起作用

Question

我写了一个简单的游戏使用Libgdx和Box2d。我的主要代码在这里：

    BodyDef bodyDef = new BodyDef();
    bodyDef.type = BodyType.StaticBody;
    bodyDef.position.set(new Vector2(mainGear.getX()
            + mainGear.getOriginX(), mainGear.getY()
            + mainGear.getOriginY()));
    body = world.createBody(bodyDef);

    float r = 231.5f;
    Vector2[] vertexs = new Vector2[36];
    for (int i = 0; i < 36; i++) {
        vertexs[i] = new Vector2(MathUtils.cosDeg(10 * i) * r,
                MathUtils.sinDeg(10 * i) * r);
    }

    ChainShape shape = new ChainShape();
    shape.createLoop(vertexs);
    FixtureDef fd = new FixtureDef();
    fd.shape = shape;
    fd.friction = 0.5f;
    fd.density = 1;
    body.createFixture(fd);

    // Dynamic Body
    BodyDef bodyDef1 = new BodyDef();
    bodyDef1.type = BodyType.DynamicBody;
    bodyDef1.position.set(200, 350);
    body1 = world.createBody(bodyDef1);
    CircleShape dynamicCircle = new CircleShape();
    dynamicCircle.setRadius(16f);
    FixtureDef fixtureDef = new FixtureDef();
    fixtureDef.shape = dynamicCircle;
    fixtureDef.density = 1f;
    fixtureDef.friction = 0.5f;
    fixtureDef.restitution = 0.5f;
    body1.createFixture(fixtureDef);

但是当我旋转大圆圈时，小圆圈仍然正常移动，就像我不旋转一样。看起来2圈之间的摩擦不起作用。我想要的是当我向右（或左）旋转大圆圈时，摩擦会拉动小圆圈跟随它。