btp is a teacher now

Oh definitely do the spinny chair trick. Arms out to slow your velocity, arms in to speed it up again. Goes great provided nobody falls out and breaks something.

Buggered if I remember the scientific principle behind this, but I'm a biologist not a science teacher.

Moment of inertia + conservation of angular momentum.

When you pull your arms in, you decrease your rotational inertia and you're "easier" to spin, so your rotational speed goes up to keep the angular momentum constant.

Edit: Bob if you share what curriculum you are supposed to cover I am sure I can come up with all sorts of demos and shiz. Do you have any budget for materials or would it have to come out of your own pocket?