First, both the balls have constant z-component of angular momentum so of course the total angular momentum is also constant. Second, the z-component of angular momentum is negative.

To compensate and keep angular momentum constant, the washer's angular velocity has to increase. The reverse happens when you loosen the string and allow the washer to move out farther.

When you bounce a tennis ball off a moving basketball, the tennis ball goes careening off at high speed. Here's why that happens.

Learn about the principal of momentum and how it can be transferred between a tennis ball and basketball.

Physics and Python stuff. Most of the videos here are either adapted from class lectures or solving physics problems. I really like to use numerical calculations without all the fancy programming ...