Brings back memories!

In my case it was a slide on an air cushioned aluminum beam.

And the interesting part was that for some reason, if we pulled it up towards the top, behind some point it used shorter time to travel across the whole beam.

I put quite some effort into figuring out why, repeating it again and again, studied the beam to see if there was any irregularities, brainstormed on why this happened.

My physics teacher really liked that at least some of his students had dug into it (I think we weren't the only group) and made it very clear in the feedback (he did not mention who had gotten it wrong, just that some had observed this and looked into it instead of covering it up or throwing away the data we didn't like).

Didn't exactly enjoy school, but people like him made it a lot better.