STEM: Slinkys and Sound

What is sound? 

That's the question that my wife and I posed to a group of about forty primarily Hispanic and African-American 4th- to 6th-grade girls. The students offered a range of accurate and insightful answers and it was immediately clear that we had a very enthusiastic and engaged group on our hands.

My wife's employer, Rocket Fuel*, runs an ongoing STEM (science, engineering, technology, and math) program for girls from East Palo Alto elementary schools, and we were honored to be able to lead a learning session for them in September. Our lesson plan included string, spoons, Slinkys, some compiled YouTube snippets, a guitar, and (of course) some microphones.

Want to make sci-fi special effects sounds with your kids in your home? All you need is a little string and a metal Slinky.

Here is a video which highlights a few moments from the class.

For those who may be interested in doing something similar, here's what we ran through:

We started the class by asking, "What is sound?" Then I strummed a few chords on an acoustic guitar and asked, "How does the guitar make sound, and how does the sound travel from the guitar to your ears?" To help illustrate, we showed a slow motion video with some clips of guitar strings vibrating, so the girls could plainly see what was happening.

We then asked, "How long does it take for the sound to get from the guitar to your ears?" Their answers ranged from 5 seconds to 1/2 a second. To actually measure how fast sound travels, we set up two microphones eleven feet apart and asked a student to clap their hands while we recorded the sound into my computer. Then we could see in a waveform view that the sound arrived at the second microphone about 10 milliseconds after reaching the first microphone. By multiplying by 100, we arrive at 1100 feet/second for the speed of sound, which is very close to the standard value at sea level and 20 °C (68 °F) air temperature. We asked how many miles per hour that is, and told them it was around 700 MPH -- or about 3 football fields in 1 second.

Then we could see in a waveform view that the sound arrived at the second microphone about 10 milliseconds after reaching the first microphone. By multiplying by 100, we arrive at 1100 feet/second for the speed of sound, which is very close to the standard value at sea level and 20 °C (68 °F) air temperature. We asked how many miles per hour that is, and told them it was around 700 MPH -- or about 3 football fields in 1 second.

The most fun of all, though, was when we brought Slinkys into the mix. First, we had the girls use wave propagation through Slinkys to visualize how sound travels through air. The girls had a lot of fun with that, pushing the waves back and forth between them (as you'll see in the video).

Then we asked the girls to do the following:
1. Take an arms-length piece of string
2. Tie it around a metal spoon in the middle
3. Wrap a bit of the ends around their fingers
4. Use their fingers to "plug" their ears
5. Bang the spoon against a table or something similar.

The result is something like a bell in a bell tower, which sounds very cool. But, the real fun came when we did the same with the Slinky with pulling a bit of the string through the top of the Slinky then dropping it. The girls faces lit up with excitement when they heard the strange sounds produced by the Slinky. (*DO* TRY THIS AT HOME -- This Youtube video shows exactly how it's done.)

We knew the class was a hit when at the end of the class, Kiwoba (head of Rocket Fuel Gives Back and an amazing role model for the girls) asked the students to say one positive word that described the class. The responses included "amazing", "fun", "mind blowing", "best class in the universe." When we talked about it later, our word was "Inspiring." There's nothing like getting a room of elementary school girls lit up about science and music to brighten your week.

* Special thanks to the Rocket Fuel Gives Back program for giving us this opportunity!