Ooh, this is a pretty fun simulation -- models how heat might flow around your house via convection.
Teaches a cool fact about convection that I'm still wrapping my head around...
More importantly, you get to move all the pieces, and I had a silly amount of fun doing that.
"Convection: The Stack Effect" by the Concord Consortium.
https://lab.concord.org/embeddable.html#interactives/energy2d/htb/S4D1.json