Ask HN: I need ideas to impress fifth graders with technology

Ever heard of Makey Makey[0]? It's crocodile-clip electronics. You can build a piano out of bananas. [0] https://makeymakey.com/

Easy. Augmented reality sandbox.

This is not so an idea of it's own. But, the thing that still wows me when I really consider it, is scales. I don't think people outside of this field ever really consider just how small and just how fast these switching machines are. It used to amaze that a programmer of an 8-bit game machine in the early 80s would know how much time they had before a certain scan line was reached, what the computer would do while waiting for the TV to reach that point that is instantaneous to us. I've seen transistor projects built up to make an 8 bit adder. The transistors taken to a higher level of logic gates. You flip switches and different lights go on or off. Then extrapolate that to a chip with a few thousand such circuits switching on and off many times a second, then extrapolate that to modern machines doing that with millions of transistors at nano scale at ghz, so that the simple act of switching circuits on and off results in say, voice recognition or AI, or drawing pixels to the screen or working out geometry for 3D graphics. The many levels of abstraction to get there. You don't need fancy things, because just the most basic machines are actually pretty amazing, and then to think that they are just 'basic'. Then there is the networking of many of these machines just to send even a text message around the world and have someone get it seconds later (let alone millions of people doing the same thing at the same time). It's pretty ridiculous to think about, but we usually take it for granted or are completely unaware of just how complex this is. And so simple at the same time. It's surely humanity's greatest achievement.

They overflow a different kind of stacks.

I don't think you can truly answer that question without it being part lie. For one, we don't necessarily know the real reason, plus there's multiple reasons anyways, especially since it's taken on a life of its own and culture/history is part of it now.