High and low notes

My youngest son has shown an interest in all things musical, and it seems to have inspired his older brother to take more of an interest too.  Whilst things like tapping a beat, and taking delight in making music and dancing seem to come naturally to the little one, the bigger one hasn't always been very keen.  However during lockdown our weekly Zoom music groups have been enjoyed by both of them, and one of the things we sometimes do is singing about high and low songs.  I thought we could try blowing bottles and seeing whether my eldest son (three and three quarters, as he proudly tells anyone who will listen!) could tell which notes were low and which were high.

I found three empty drinks bottles, plus an empty and well washed tube from some bubbles.  I showed him how to blow across the top so that it makes a sound.  He didn't find this at all easy, but remarkably he persisted until he got the hang of it.  

Blowing a small bottle

When you blow across the top of the bottle, some air goes into the bottle, which increases the pressure inside and pushes air back out again.  The air you are blowing is moving fast and this creates low pressure which sucks the air inside the bottle out, until the pressure inside the bottle decreases enough to suck the air stream you are blowing back inside again.  This results in the a vibration, and our ears hear vibrations of air as sound.  We've previously explored sound using a speaker from an old CD player, and my son felt how the speaker wobbled backwards and forwards when he could hear it making a noise.  If you take a big bottle, there's a lot of air inside and the time taken for the pressure changes is longer, so the vibration is slower - this is a low (deep) sound.  For a small bottle, the vibrations are faster and it sounds higher pitched.

Blowing a bigger bottle

My son and I each blew the bottles, and listened to the sounds.  I asked him to compare pairs of bottles and say which one made the lowest, deepest noise.  Whilst blowing in the right direction, with enough force, was a bit of a challenge, it turned out that he was easily able to identify the differences in pitch, and ordered the four bottles from high to low.  I also got him to put his hands around the largest and smallest bottles as I blew, and he felt the slower and faster vibrations.

In order from lowest (L) to highest (R)

This was a nice simple activity with very little preparation, and was fun to do, with my son enjoying learning a new skill - blowing across the top of the bottles to make a sound - whilst learning a bit of science too.