These questions should all be answerable, some with a lot of research and some with very little. Maybe some of them would make good 10-minute talk topics. All make good physics review.

1. Just before they burst, soap bubbles lose their color and become very transparent. Why?
2 . The flame of a candle or a match is of colors that vary from the bottom to the top of the flame. Why?
3.  Why does our smoke detector go off just before a lightning strike? (It's one of the Am-241 types.)
4.  You stand on a bathroom scale and read your weight. If the air were pumped out of the room, would the scale's reading change?
5.  How tall a drinking straw can you use? Does it matter if it's twisted?
6.  I can get one set of notes out of the headpiece of a flute (this is a cylinder with a hole you blow into/over, and the other end open.) normally, but if I close off the other end, I get another set of notes. How are they different, and why?
7. Estimate the Fermi energy of copper.
8. Can one photon turn into an electron-positron pair?
9. What is the point of a throwing stick, or atlatl?
10. We have two chimes, one that vibrates at 440 Hz and one at 441 Hz. If you put them near each other and whack one of them, of course it chimes; if you stop it, you can hear the other one ringing, too. Strangely, if you whack and stop, sometimes the other chime is barely vibrating, sometimes it's got a pretty good amplitude, although never as strong as the whacked chime. Explain all this.
11. Explain the phase lag between tides and the moon's position.
12. Explain rainbows, including double rainbows. If we lived underwater and there were an airshower (I guess fine bubbles rising?), could there be a reverse rainbow? I mean, would we see sunlight, or other white light, broken into its constituent colors?
13. Why do different planets have different atmospheric pressures?
14. Derive the altitude dependence of atmospheric pressure using mechanics considerations. You may assume constant temperature, although you ought to include some estimate of how much difference that makes. Show that your results agree with what you'd predict from purely thermodynamical considerations, if they do.
15. I'm not very happy with the treatment of group velocity in most textbooks. See if you can do a better job of justifying the statement that group velocity is d-omega/dk.
16. How much energy is absorbed by a car's shock absorbers during braking? Do the shock absorbers affect stopping distance?