A person standing on a turntable while holding a bicycle wheel is an excellent laboratory to observe angular momentum conservation. A person is initially stationary on the turntable, and the bicycle wheel is rotating about a horizontal axis.

Initially, the angular momentum about a vertical axis is zero.

The person re-positions the wheel so its rotation axis is vertical. What happens?

1. The person remains stationary.
2. The person rotates in the same direction as the wheel.
3. The person rotates in the opposite direction as the wheel.

Since there is no external torque acting on the system, the total angular momentum must remain zero. The person spins in the opposite direction as wheel.

Re-positioning the wheel so its rotation axis is horizontal again should stop the person's rotation. Flipping the wheel over so that its rotation axis is again vertical but reversed will make the person spin in the opposite direction.