Sound and Vibrations 1: Rubber Band Guitar

Background Information for Teachers

We are surrounded by sounds every day. Sounds are caused by vibrations, or the rapid back-and-forth motion of an object. These vibrations are transferred to the air molecules right next to the object, which bump into the molecules next to them, and so on, until the vibration reaches our ear (Fig 1).

Image Credit: Ben Finio, Science Buddies / Science Buddies

A vibrating object causes air molecules around it to vibrate. The air molecules are pushed together in a wave pattern that travels to our ears, and is interpreted as sound.

Figure 1. Diagram of how sound travels as vibrations (air molecules are not drawn to scale).

Sometimes, these vibrations are obvious because they are big enough to see. For example, when you pluck a rubber band, you can see it move back and forth (or if you turn up the bass on a stereo with a large subwoofer, you may be able to see the speaker move). However, for the majority of sounds we hear every day, these vibrations are too small to see. For example, when you knock on a door, even though you can hear a sound, you can't see the door vibrate at all. Sometimes you can still feel these vibrations even though you can't see them. For example, if you place the palm of your hand on a door while someone else knocks on it, you will feel the knock. You can also feel your vocal cords vibrate if you put your hand on your throat while you talk!

In this lesson plan, students will first explore how sounds cause vibrations using vibrations that are easy to see (with rubber bands). Then they will explore other vibrations that are harder to see, like knocking or talking. Finally, they will make their own sound and explain what vibrates and causes the sound.

Additional Background Links

• Physics for Kids: Basics of Sound, Ducksters

Prep Work (10 minutes)

• If you are using tissue boxes, make sure all the tissues are removed.
• If you are using cardboard boxes, use a box cutter to cut a hole in the top, and tape the lid flaps shut.

Engage (5 minutes)

1. Tell your students that today they will learn about sounds. First you want them to think about the question "what is sound"? Make a few sounds using objects in your classroom (e.g. clapping your hands, writing on a chalkboard, flipping the pages of a book). Now ask a slightly different question: "what causes sound?"

   Turn to your partner and explain what you think sound is, and what causes sound.

2. Call on a few students to share their answers for both questions with the class. Answers could include, for example, "sounds are noises that we hear," "sounds happen when we talk," or "sounds happen when two things hit each other."
3. Explain that now we will explore what exactly causes sound.

Explore (20 minutes)

1. For each pair of students, one student should hold one end of the rubber band in each hand and stretch it out. The other student should gently pluck the rubber band with one finger. Let the students try this a few times. Ask the class these questions:

   What do you hear when you pluck the rubber band?

   We hear a sound.

   What do you see?

   We see the rubber band move back and forth.

   What happens when the rubber band stops moving?

   The sound stops.

2. Explain that the fast back-and-forth motion of the rubber band is called a vibration. When you pluck the rubber band, you make it vibrate. The rubber band in turn pushes on the nearby air, making it vibrate. Even though you can't see the air vibrating, your ear can hear it. The vibration causes the sound. Since the vibration causes the sound, when the vibration stops (the rubber band stops moving), the sound also stops.
3. It's a little annoying if one person has to hold the rubber band all the time. To make this easier, each group can build a rubber band "guitar," shown in Figure 2.
   1. Stretch the rubber band around the tissue box, so it goes across the opening at the top.
   2. Place one pencil/crayon/marker under the rubber band on each side of the hole.

Image Credit: Ben Finio, Science Buddies / Science Buddies
Figure 2. A rubber band guitar.

4. Now each person can hold the box with one hand and pluck the rubber band with the other hand. Let students take turns doing this and explore with more observations. For example, what happens if they use their finger to stop the rubber band from vibrating? How does the sound change if they pluck the rubber band harder?
5. Demonstrate knocking on something hard in your classroom, like a desk, door, or wall.

   What did we hear?

   We heard a sound.

   What did we see? Could we see the vibration this time?

   No, we could not see the desk vibrate.

   Do you think that there is still a vibration, even if we can't see it?

   Student answers to this last question might vary. They might not believe that there is still a vibration if they can't see it.

6. Explain that all sounds are caused by vibrations, even if we can't see them. To demonstrate this:
   1. One student should put their hand flat on a desk.
   2. The other student should knock on the desk.
   3. Switch roles and try again.

   What did you see, hear, and feel when your partner knocked on the desk?

   We heard a sound. Even though we couldn't see the desk vibrate, we could feel it vibrate with our hand.

Reflect (5 minutes)

Explain that most of the vibrations that create sounds are too small for us to see. The rubber band provides a good example of vibrations because the vibrations are very big, so we can see them easily. Now revisit the questions you asked at the beginning of class.

Tell your partner what you think sound is, and what causes sound. Did your answers change based on what we did today?

Assess

To assess your students' understanding of sound and vibration, ask each pair of students to think of a sound they can make in a classroom (other than plucking their rubber band or knocking on a desk, which they've already done). Examples could include talking, tapping two pencils together, scratching their clothing etc. Then, ask them to explain to the rest of the class what vibrates to create their sound, and how they know this (e.g. can they see or feel the vibration?).

Make Career Connections

Discussing or reading about these careers can help students make important connections between the in-class lesson and STEM job opportunities in the real world.

Automotive Engineer

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• Read More

Career Profile

What do sound and vibrations have to do with cars? A lot! Cars have lots of moving parts that vibrate. Engineers have to figure out how to decrease these vibrations so the ride is not too noisy and bumpy for the passengers. Read more

Lesson Plan Variations

• Let students experiment with their rubber band guitars to see what different types of sounds they can make. What happens if you pluck the rubber band harder? What happens if you move the pencils closer together or farther apart?
• Have students put their fingertips on their throat as they talk, hum, or sing. Can they feel the vibrations? Note that this could be a little confusing, because you can see a person's face, mouth, and throat move when they talk. However, those motions are not the vibrations that cause sounds. The vibrations come from our vocal cords, which are inside our throats.
• Identify more sounds around your classroom or school and figure out what vibrates to cause the sound.