Hey there, kiddo!
Have you ever made cupcakes? When you put them in the oven to bake, you usually put them on a tray and then put the tray in the oven, right? Well, a rotating furnace is kind of like a very big and very special oven that rotates as it heats things up.
Picture a big cylinder-shaped oven with a door at one end that you can open and close. Inside that cylinder, there's a kind of special tray that can hold all sorts of things you might want to heat up or melt down. Now, instead of just sitting in the oven, that tray can spin around and around.
Why would you want that? Well, imagine you're trying to melt down a bunch of rocks to make metal. If you just put them in a regular oven, they might not get hot enough in some places, or they might get too hot in other places, and you would end up with uneven and not very useful metal. But if you put them in a rotating furnace, the tray would spin around and make sure that everything gets heated up evenly.
And that's pretty much it! A rotating furnace is a big oven that can spin around as it heats things up, making sure everything gets evenly heated.