Spinning pendulum

From: https://stevespangler.com/experiments/unbelievable-pendulum-catch/

Assemble the device:
Weigh the small nut. Assemble large nuts to weigh 14 times the small nut. (Or separate one washer from a group of 14 washers.)
Cut string or wool to 80cm. Tie the small nut (or single washer) on one end of the wool. Tie the large nuts (or 14 washers) to the other end of the wool.

Hold out a pencil (works better than the straight finger in the photo) and loop the weighted wool over it.
Hold the small nut out to the side (see photo).
Drop the small nut. As it swings downwards, the heavy nuts pull the wool over the pencil, and the small nut wool shortens and wraps around the pencil.
The swinging small nut on the wool has angular (circular) momentum as it is let go. As the length of the wool shortens the small nut goes faster (because the 'angular momentum' has to stay the same). The small nut goes so fast that it wraps the wool completely round the pencil, and keeps wrapping as it gets faster and faster. The tightening of the layers of wool around the pencil creates friction which stops the wool from sliding over the pencil, so it wraps up completely.

Try playing with variables:
How out to the side does the small nut need to be dropped from for it to work?
How long does the small nut wool need to be for it to wrap enough times making enough friction to stop it from slipping around the pencil?
? Measure the smallest angle needed for it to work.
Encourage students to play around, remembering to only change one variable at a time to determine if it affects the outcome.

If the small nut is not held out to the side at the beginning, but straight down, the heavy nuts fall to the floor (as the small nut wool does not wrap around the pencil).