A small object is sliding inside a circular frictionless track. At point A another frictionless track switches it to a smaller circle (see the picture). At all times the tracks can only exert forces which are perpendicular to the motion of the little slug. Does the angular momentum of the little slug change or does it remain the same as it moves from the large circle to the small one?

Suppose you are standing on the edge of a spinning carousel. You step off, at right angles to the edge. You learned in the last preflight that this has no effect on the rotational speed of the carousel.

Now consider it the other way. You are standing on the ground next to a spinning carousel and you step onto the platform. Does this have an effect on the rotational speed of the carousel? How is this case different from the previous case?

The mass of the Earth is about 6x10²⁴ kg and its radius is about 6x10⁶ meters. Suppose you are building a runway along the equator and you line-up a million 10,000 lb airplanes^s and give them all take off simultaneously. Estimate the effect that would have on the rotational speed of the Earth. (Note:the mass of a 10,000 lb airplane is about 4,500 kg.)