What do pianos and rubber bands have in common? In this lesson, kids get a chance to really explore and play with sound!
I wrote the question: What does the transfer of energy and sound have to do with one another? I asked the question out loud and told students not to answer it just yet. I opened up the lesson today with turning on the Piano Guys Christmas Video because it showed them playing inside of the piano. It's an awesome video and exposes kids to the sound waves created by a percussive instrument. I told them that I wanted them to pay close attention to how sound was created both inside and outside of the piano by plucking or hammering strings.
Put on the Science Cap: I told my students that we had seen this video at holiday time, but this time I wanted them to look at it through scientific eyes. I instructed them to list in their notebooks how many different ways they saw the piano being played. I wanted them to think about the following questions: I listed them on the board.
What are the black things with the white felt that go up an down inside the piano? What do you think they do?
How do you think the keys work in a piano? Could you sketch in your mind what you think the inside of the piano looks like that you can't see?
What is the hairy looking stuff that is first used and how does that work?
What does the paper do? What do you think helps transfer the sound out?
How do you see energy turning into sound waves?
We we were finished watching the video, I explained that I was going to play it again without the sound this time. They were to watch silently and see if they missed anything.
We discussed the difference in what they noticed and that with the sound missing, they saw other things. They mentioned the "stringy, hairy thing" as I explained that it was the part of a bow from a cello called the "hair". It is the part the musician moves over the strings. They mentioned the pedals, thinking that the sound came from them. I clarified what the dampers were, that they were the black and white things that they saw inside the piano that moved up and down stopping the sound mechanically when the pedal is off. But, when the pedal is pushed down, the sound waves continue. I explained that in an acoustical piano there is a mechanism that raises the damper as the key is struck. I told them that they could research the Explain That Stuff page, if they wanted to know more about how a piano works. We had a pretty detailed conversation about the piano so I had to bring it back to the idea of sound waves.
I continued with questions. How did the sound waves get out of the piano? Where was evidence that energy was transferred?
One student said that the energy from the piano just comes out! I asked where the energy was coming from first? They said that all the things the guys were doing to the strings. Someone said vibrations! I told them that they were going to explore first hand how these vibrations create sound waves. Exposure and investigation of these next steps support the crosscutting understanding of energy and the interdependence of engineering and technology.
Because I do not have an acoustical piano in my classroom, I brought a mountain dulcimer to my classroom to help draw the concepts to reality and expose them to a different type of stringed instrument. They were immediately engaged! ( I could have used my guitar or borrowed one from our music teacher. If you don't have access to a dulcimer, a guitar or any stringed instrument would do. An acoustical piano would be ideal! Open up the inside and use the piano much like Piano Guys to demonstrate the vibration of the strings.)
Set the Stage: I pushed desks around so we had enough room to sit in a circle. I seated myself on the edge of the circle with the rest of my students. I asked them to bring their notebooks and they sat down quickly. They were interested in what was in my slender music case. I popped the closures and dragged out my mountain dulcimer. I heard excited roars of "What's that?" I love fourth grade because you can bring out things like this and totally floor them. I can work magic, no matter how simple!
I explained that the dulcimer is an American instrument that was developed from something called a cymbalom, from Hungary. The hammered version is a cousin of the piano. I began to tune it. Two strings were off and I asked them to listen and tell me when the sounds matched. They caught on quickly. I fussed with making it flat and then sharp until the sound matched and then asked, " How do you think I got it to match?" I sat for a few minutes and let them listen to a few mountain songs I could pluck out. We talked about how the energy of the sound waves have amplitude just like our water waves. When the two sounds have the same amplitude, the pitch will match.
I stopped and asked how energy played a role in creating the sound? They told me the energy came from my hand and that it was transferred into the strings. I then ran my finger up the fret and created higher pitches. I asked why they thought the pitches sounded higher? Was I applying more energy or force? This question was important because I suspected my students may have some misconceptions about the difference between pitch and volume. When I was tuning it, one student made the remark that the strings sounded the same because I was hitting them harder. I asked if they noticed the inside of the piano and the length and thickness of the strings?
One student said that the longer the string, the lower the sound. So I moved my finger down the fret proving him correct.
I asked them if they wanted to make their own instruments?
Various plastic & cardboard box type containers
Lots of rubber bands ( I used three packages to divide. I didn't want anyone to feel they couldn't use as many as they needed.)
I told students that they would be able to create a musical instrument with the materials on the floor. One rule was that they could not use the rubber bands for anything else! ( Like shooting or snapping ach other!)
Work in Partners: They chose their partners and the types of box they wanted to use, along with handfuls of rubber bands. They quickly began to figure out how they were going to create an instrument from their materials. I observed joy as I started to rove and got the camera rolling because only the camera could really describe what was going on at that point! One group came to me because they were worried about being right. Because my goal was that they would learn about how sound waves work through experience, I reassured them that there was no right or wrong, only trying and testing. I enjoyed watching students explain how rubber bands can make sounds. One student explained "See how its making waves?" to his partner. As I stopped and visited, we had discussions about how different materials make different sounds.
Questioning: I used strategic and unplanned questioning that I have noticed drives instruction effectively and pushes their inquiry and motivating them to try all kinds of ways to string the rubber bands. Trying out the sounds and experimenting with pitch and dynamics was important for their learning. I gently guided them to pay attention to the length of the strings and the sounds they made. Inevitably, the longer strings were making deeper pitches, but many confused pitch and dynamics. So I needed to demonstrate how force was the determiner of the dynamics.
I stopped everyone when I thought they were all finished and told them to write down anything they noticed as they put their instrument together. We gathered in the circle and each pair of students demonstrated their discoveries about their instrument. One pair had used an ice cream bucket and a square container. We listened to the differences in the two and discussed the shape of the container.
I asked, " Do you think shapes of the instrument's case or body makes a difference in how energy is transferred within the instrument?" I wanted them to think about why violins are shaped the way they are and why my dulcimer is hour glass shaped. Why are some pianos completely square and why is a grand piano shaped the way it is? I explained that even with a piano, the sound is different in a grand because the hammers have to raise up to hit the string, where a console the hammer goes down to hit the string producing a different tonality. Strumming vs striking a string makes a different sound.
As we went along in the groups I asked if they could produce a different tone or type of sound from the instrument. They all experimented. They demonstrated by removing some of the rubber bands. We discussed why we couldn't hear sound as well from the book boxes that had holes in them and surmised that the holes affected how well the sound traveled. The boxes contained the energy and sound waves. They enjoyed demonstrating how two different containers sounded. I asked why they thought why that was and we talked about the sound waves bouncing inside the box. We also discussed how the stronger the force the louder the sound and that it was this force that produced the dynamics.
We stopped and had a rubber band band concert! It was so awesome! Then, I asked them to meet with their partner and respond to this question: How did you see the transfer of energy happening in your instrument through sound waves?
When all was done, we took a look at another Piano Guys video where we could again see the inside of the piano. We pulled apart our instruments dancing to the music.
In order to assess their personal understanding, I asked students to write a "quick write" in their notebook describing what they had learned about sound waves, pitch, tone and dynamics. Students wrote for about 5 minutes and left their notebooks open on their desks for me to check.