How Does a Blade of Grass Produce Sound?

The grass I used for my experiment

Grass Whistling

I found the grass I used outside of the geography building

I remember when I was young my mom took a blade of grass between her thumbs and blew, and it produced a whistle sound. I have always found that to be fascinating and I’m curious as to how this is possible.

How Does it Work?

Technically, a grass whistle is a form of reed instrument that resembles woodwind instruments, like the clarinet and uses the same science as woodwind instruments, beginning with the fundamental idea that vibration causes sound (Smyth, 2021).

This is due to Bernoulli's principle, which explains how the pressure of a moving fluid (in this case air) decreases as velocity increases. In the air, molecules are always moving, creating pressure. There is an upwards force which means fewer collisions downwards. When blowing onto the blade of grass in between your thumbs, you can increase the pressure to cause more airflow and create a louder whistle.

Similar to a reed, due to the Bernoulli effect when someone blows onto a blade of grass causes the grass to move up to block/reduce airflow and stops the grass from down again; this cycle of pressure fluctuations cases the grass to vibrate rapidly back and forth between your thumbs, which in turn causes wave compressions of the air molecules surrounding the source producing a whistling sound.

Graphs

Time Graph: there is a visible pattern, that is jagged.

Format Graph: Shows the frequencies present, it's interesting how the frequencies are still present even over quite a bit of time. The harmonics decrease slowly

Spectrum Graph: The fundamental frequency present is f1 = 1716Hz, followed by f2= 3321Hz, f3= 5097Hz and f4= 6719Hz. The frequency is clearly increasing, without much of a decrease taking place once the sound is emitted.

• How does one blow through a blade of grass compared to a harmonica or a trumpet?

Honestly, the most important thing is to make sure the blade of grass between your thumbs is held tightly so it isn’t floppy. Then have your thumbs close to right by your lips and blow as hard as you can, making sure the blade of grass isn’t touching either side of your thumbs helps to produce a louder sound.

How to Grass Whistle

In order to grass whistle you have to pick the right thickness of grass. A blade of grass that is too thin won't be able to produce any sound when blown on. It can be challenging at first, you have to make sure that the

the grass is thick and that when placed in between your thumbs that the blade is tightly secured.

If done properly it sound like this:

Here's an image that describes grass whistling:

How to position your thumbs in order to grass whistle