But the demo stayed with me, and I worked it into my curriculum early on. It was my first Show & Tell at an NCNAAPT Meeting (Spring 1992, American River College, IIRC).
I think it's a great demo for the Newton's Law unit. There have been times when securing toy dart guns was a challenge. They can last for many cycles, but they were built as inexpensive toys, not precision science apparatus. Fortunately, Arbor Scientific has become a reliable source.
I wrote a post about this demo previously, when I recorded some nice high-speed video of it. It includes a few more specifics.
Here's the RT;DL stuff:
Google Doc: Demo - The Newtonian Shot
HTML Preso: Demo - The Newtonian Shot (including convenient Zoom participant reaction instant poll)
As ever, my presos are designed to support my storytelling and do not stand on their own terribly well. (Like a backup band with no lead singer.) And you can see I use aluminum support rods to help with the simultaneous launch. I launch the darts from ceiling-level down to my countertop so students can see the landing point. I protect my concrete countertop with a wood plank.