Noisy noisy balloon

I found a fun sound experiment where you drop a nut (the metal type) into a balloon and inflate the balloon. When you shake the balloon you can get the nut to circle around inside, making a neat whirring sound (thanks to the repeated pattern of the edges). Jr scientists A and E had fun playing with this one. Making the sound is clearly easy enough for a baby - Jr scientist E had no trouble making it go. The only downside is that the nut starts to make tiny tears in the balloon after a few minutes, resulting in an increasingly small (and less fun) balloon. Maybe we should start buying balloons in bulk.

Musical bottles

Today we turned bottles into whistles (blowing air across the top to make a note - a bit beyond the abilities of jr. scientist A). We added and removed water from a bottle to see how it changed the note we heard. As we added water (i.e., less air in the bottle) we got higher notes and as we took away water we got lower notes. We then tried to figure out if other things besides how much air was in the bottle affected the note we got. We took three different types of bottles (a wine bottle, a glass coke bottle, and a plastic water bottle). We filled both the wine bottle and the water bottle all the way with colored water. We then poured enough water out of the wine bottle to fill the coke bottle, emptying out the coke bottle afterwards. We did the same thing with the water bottle. This way, all three bottles had approximately the same volume of air in them. We then made a note on each bottle and got three very different notes! I think I was more excited about this than my son - it seemed to be a bit too advanced for a toddler - but I thought it was really cool. Clearly the shape/size of the bottle and the volume of air in the bottle both matter.

Tin can phones

We had some empty giant coffee creamer plastic containers so we decided to make some "tin can" phones. We had made some before using paper plates, string, and popsicle sticks (wrapping the string around a popsicle stick up against the plate), with limited success. The coffee creamer containers worked much better, probably because they captured sound better and added their own funny-sounding resonance. We also figured out that we could use one of the containers as an amplifier so when we strummed the string between the two "phones" we could hear a clear note come out of each container - a good example of how the string was transporting vibration and the containers were turning those vibrations into sound (o.k., technically the ear was turning them into sound and the containers were just amplifying and modifying the vibrations). Overall I'd say it was a fun experiment that worked well.

Rubber band guitar

Materials
Kleenex box
rubber bands
pens

Results
Success

Working theory

Sound results from periodic (i.e. regular) vibrations. Changing the length, thickness, or tautness of a rubber band should change how it vibrates and what pitch it produces.

Experiment

We started by placing different sized rubber bands around an empty Kleenex box, strumming the part of the rubber band that was over the opening of the box (where the Kleenex come out). This created a muted and muddy sound. Thinking the rubber band was up against too much of the box, preventing sustained vibrations, we moved two pens under the rubber bands and strummed in between them, making a nice note. By changing the distance between the pens (lengthening or shortening the part of the rubber band that vibrated), we were able to systematically change the pitch we got.