Working with what you have lying around to demonstrate curios scientific principles in an engaging ways is quite fun and can be quite fun for the kids.
My father used to do this a lot and I had gotten so curious about different types of things that I think he ended up drawing how the internal combustion engine works for me on a napkin when I was 6 or something like this.
His drawing from then is still my immediate mental reference as far as the inner workings of an engine goes.
Demonstrating something cool and asking the kids to try and explain it themselves before you give them the explanation is what makes it the most fun and the most memorable for them I think.
Hey, Dave, Thank you for your visit, your comments, and especially this particular "extra" point. Asking them questions is a great way to get them thinking!
Your dad sounds like a good man. :D
As always, it's my pleasure :)