Auto Mechanics to Quantum Mechanics: Any Questions?

It's been a while, so here it is again.

For those new to the Playground, I have a schtick I do at the beginning of each class where I let the students ask absolutely any question they have, any question at all, from auto mechanics to quantum mechanics. Some former students asked me to revive it on-line, so every couple of months I trot it out here. So, if you've ever had a question you always wanted to ask or something that's just been stumping you, here's your chance. Ask away and I'll get to as many as possible in this week's posts.

Here's one for you guys: homonyms are words that are spelled differently, but pronounced the same, for example, led and lead. Is there a word for words that are spelled the same, but pronounced differently? Think polish and Polish -- there's a big difference between silver polish and Polish silver.

So, what do you have for us? Any questions?