Sail and Prop - 3rd Law

The dynamics track cart has a sail and a battery operated propeller; both are removable. If the propeller is removed and held so it blows against the sail, the cart will roll to the left. If the sail is removed and the propeller mounted alone, the cart will accelerate to the right. If both the sail and the propeller are mounted, the instructor can ask the students which way the cart will roll.
From S.R. Smith and J.D. Wilson, Phys. Teacher, Apr. 72, pp 208.

Note: The above demos may also be demonstrated with the air track at the instructor's request. The air track has an advantage over the dynamics track in that there is less friction associated with it. However, the air track has a draw-back in that it is much nosier than the dynamics track and in a lecture setting it is difficult for the instructor to be heard.