[RiderOfGiraffes]

Your second experiment is absolutely fantastic, and I have used it. I was disappointed to find that the kids actually seemed to learn nothing from it. The principles seem to be pretty deep, and there's actually a lot going on. Maybe I didn't explore it enough, but I think it's a difficult experiment to "get" until you're older.

Your first one is easiest done with a "slinky". You don't need a strobe, because it all happens really, really slowly.

Off-topic: Some people are like slinkies. Of no real use, but they still make you laugh when you see them tumble down stairs ...