OK, so that’s maybe a little over-the-top. Still, today we mostly did science experiments having to do with acoustics.
I had been planning to just do some experiments around the house, but Alex expressed interest in going back to the Maryland Science Center, and I knew they had some nifty things to try there, so I shifted gears. We arrived not long after opening, and moved on up to the 3rd floor, where all the various sensory experiments are. I told her that we were going to try an experiment, called a “whisper dish”, and she was eager to take part.
If you’ve never seen one of these, it’s a matched pair of parabolic dishes (about 7 feet in diameter) facing each other across a good-sized room, maybe 60 feet apart. There’s a ring on a post to indicate the focus of the parabola, and if you speak close to that, then the sound carries to the other point and is amazingly sharp. We played with it for a while, and I explained how sound bounces and is collected, and she thought it was just really cool. We messed around with their other sound-themed experiments (including a theremin), but nothing else was as cool as the whisper dishes. We did try listening to our voices while standing next to a normal wall on one side of a hall, and listening when we stood next to an anechoic wall on the other side, which gave an interesting “deadness” to the sound. The kids played in the “kids’ room” for a while, and we came back home.
After lunch, while Colin was napping, I showed her how sound could be directed from speakers by letting her sit in my desk chair and listen as I moved the desk speakers around. We talked about the difference in loudness and in the tonal differences, including what happens if objects are between you and the sound source; afterward, I also showed her how you could get a lot of the “muffled” sound if you stood in a closet with lots of clothes as opposed to standing in a tiled shower. We then went downstairs for our final experiment.
I took a bowl about a foot in diameter, and stretched plastic wrap over the top, using a rubber band to hold it in place, thus making what was essentially a thin-skinned drum. I helped Alex liberally sprinkle table salt all over the plastic, and we set it on the counter where she could see. I then picked up a small saucepan, and we held it near the “drum”, and struck it sharply with a spoon. The resulting sound waves made the salt *dance* on the plastic, especially when you struck it in rapid succession.
We kept repeating this in different ways to see what would happen. I held the saucepan close, then further away. I used my finger to clear a path in the salt, and then we watched the salt eradicate the neat lines. It was obvious that the sound was causing the salt to dance, but it was also obvious that the saucepan wasn’t touching the drum, either. This was explicit proof that sound waves travel through air, and that they can produce results when they encounter something else.
I alluded to future lessons, where we’d discuss what other situations might arise where we saw sound strike a membrane, or observe sound waves traveling through some medium. It was a big hit, and Alex was eager to demonstrate the experiment for Rivka when she got home. I loved that I was able to get across a fundamental principle in such a way that there is absolutely no doubt that she gets this, deep inside. I’m hoping that we get to do something soon where I can reach back to this, so she’ll start seeing science as this big interconnected thing, and not just a collection of neat tricks.