We are talking about air these days.
We can use straws to get air to vibrate.
Each straw has the top cut into a point.
We can squeeze the point of the straw between our lips and make the straw vibrate.
The longer the straw the lower the note and the shorter the straw the higher the note.
Next we used our straws to make bug sprays.
When you put a straw into water, the straw is filled with water and air.
At the top of the straw is air too.
If you blow the air at the top of the straw away, air and then water rush up the straw to take the place of the air that was blown away.
If you keep blowing then the water at the top of straw turns into water droplets and you have a spray.
This is how all sprays work.
We can show you how to do this at home.