light and sound By S.

light - flashlight and mirror experiments to see how light reflects, testing materials to determine whether they let light through (opaque, etc.), kaleidoscopes from film canisters and microscope slides

sound - make a simple tuned musical instrument with rubber bands (or could be more complex), getting everyone to hold a ruler over the desk edge a different length and then "playing" them in order to make a song (cool!!), using a tuning fork to show vibrations

When I taught eighth grade optics, we did other things that I can't recall TOO well, but I remember designing a floor plan for a funhouse with a cashier in the middle and say 10 arcade machines and you had to put mirrors in so that the cashier could see every exit and arcade machine. They made periscopes. Also we tested the speed of sound on a soccer field.

This is a neat unit! There are some good websites out there for optical illusions. Plus the students find colour blindness and vision problems (near/far sightedness) interesting.

Good luck!