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How Instruments Work

Developed by W. K. Adams

Students use their background knowledge to make generalizations about how musical instruments work.

Science Topics
Sound
Vibrations
Resonance
Frequency

Process Skills
Observing
Scientific inquiry
Comparing
Predicting
Inferring

Grade Level
6-12

Preparation
Complete Musical Instruments part 2

Set-Up
5 minutes

Activity
45 minutes

Clean-Up
5 minutes

Learning Goals
Students will be able to…

describe resonance and where and how it appears in instruments
describe sympathetic vibration and how it relates to instruments
use what they have learned to determine how instruments they have not studied in class work

Materials Not in Kit
3 long pasta noodles*
3 raisins or small marshmallows

Optional Materials
Projector

*You might want some extras in case they break before you want them to.

Set-Up
Watch the pasta noodle demonstration video for instructions on doing it in class.*

*The pasta demonstration video can be shown to the class, but it is more effective to do it for them in person.

Introduce the Activity
Explain that this lesson is a follow up to the two musical instrument activities. Students can either work individually, or in partners/small groups to begin the activity.

Doing the Activity
Group Work

1. Have the students think about their straw and cup instruments to answer questions 1-3 on their worksheet and discuss their answers with their partners/groups.

2. Before answering question 4, facilitate a class discussion with the following information:

a. The straw instrument and the cup instrument made sound via source of vibration. For the straw it was the reed buzzing and for the cup it was the plucking of the string that caused it to vibrate.

b. To change pitch, both the straw and cup instrument needed the length to be changed. For the straw, making the tube longer make a lower pitch and with the cup, plucking the string at its longest made the lowest note. Also the cup instrument pitch could be changed by increasing the tension of the string.

c. To make them loud – amplify the music – the straw instrument has the tube. The vibrations resonate inside the tube which amplifies the sound. With the cup instrument, the cup made it loud. the string made the cup vibrate and the cup has a lot more surface area to move the air, making the louder sound.

d. The guitar also has a source of vibration (plucking the strings), a way to change pitch (string length or tension) and a way to amplify the music (the hollow body that vibrated when the string vibrates) NOTE: the electric guitar was not loud because it does not have a  way to amplify sound without an electric amplifier.

 

Resonance and Pasta Noodles

This demo was already done in the Sound and Music lesson, but you should do it again here to remind them and help them visualize resonance after they’ve had the experience playing with the different instruments.

1. Call the students back to attention to show them the pasta noodle demonstration

2. Put the raisins or marshmallows at the end of each pasta stick

3. Hold three sticks of pasta at the opposite end of the raisins/marshmallows, each at different lengths

4. Shake your hand slowly, and the longest pasta stick will swing vigorously

5. A high frequency will cause the shortest to vigorously wave back and forth

6. Doing any frequency fast enough will cause the pasta to snap
→a good example of this is how earthquakes affect buildings

7. After observing the demonstrations, students should talk to their group to answer questions 5-6

8. Facilitate their discussion with the following information:
→ For question 6, the analogy of a swing works well. If you push on the swing at the right time, the person goes higher and higher and that’s how resonance works.  Just as the pasta noodle is about to bounce back to the other side, your hand gives it a push in that same direction. Each time the pasta bounces back, you give it another little push. That means it will keep going farther and farther each time. That’s why you have to wiggle your hand at the right rate. If you push at the wrong time, it’ll screw up the wiggle. Just like a swing. If you push at the wrong time, you mess everything up and the person barely swings at all.

Resonance and Instruments

1. Students will describe where resonance happened with each of the instruments used in previous lessons for question 7:

• straw Instrument – in the tube
• tuning fork – on the tines
• cup instrument – on the string
• voice – in the vocal folds
• guitar – on the strings

For question 8, students will compare two scenarios discussing the body of an acoustic guitar. Facilitate a discussion with the following information:

→ Jasmine is correct. If the body of an acoustic guitar were vibrating because of resonance, it would only be loud for one note. The natural frequency. Instead, it is loud for the entire range of notes that the guitar can make. So it’s sympathetic vibration that amplifies the guitar.

Resonance vs. Sympathetic Vibration

1. Students will need to discuss and determine whether sympathetic vibration or resonance is what makes the instruments loud.

Instrument Source of amplification
straw instrument – resonance in the tube
tuning fork – no real amplification, only resonance on the tines
cup instrument – sympathetic vibration of the cup
your voice – somewhat complicated; your throat & mouth provide a place for resonance to amplify the sound, your nasal cavities all contribute as well
acoustic guitar – sympathetic vibration in the body
electric guitar – no amplification unless plugged into an electric amplifier

How Does a Pipe Organ Work?=

1. You may want to project the following picture so students can see the image better than the one printed on their worksheet.

2. Students will examine the picture try to explain how they think a pipe organ in a church works and why it has different pipes.

3. After they have discussed their answer with their classmates, give them the following information:

→ Each tube resonates at specific frequency or pitch. That means there is one tube per note that the organ plays. The source of vibration is air that is pushed through the pipes, which is called wind. It’s a continuous source so the note can be sustained as long as the key is depressed. What makes it loud is both the resonance in the tubes and sympathetic vibration of the case.

Key Lesson Terminology
Vibrations (oscillations) – a shaking back and forth movement

Resonance – a natural frequency of vibration determined by the size and shape of an object

Sympathetic vibration – when a vibrating object is put into contact with another material and makes it vibrate. This is a transfer of energy and is how an acoustic guitar amplifies sound. This strings cause the body to vibrate via sympathetic vibration, which moves more air than the strings along so it’s louder.

Pitch – How low or high a tone is to a person

Tone – a musical sound of a specific frequency or pitch

Modifications
Visually impaired students may need a church organ to be described to them

Hard of hearing students can feel vibrations, and use what they have felt to answer the questions

Have students use the pasta and raisins themselves to investigate how different lengths of pasta, different numbers of raisins or even combining multiple pasta sticks to a single raisin changes the frequency that causes them to resonate.

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