Physics of Sound: How does length affect pitch?

Medora Gruber
Faithful Shepherd Catholic School, Eagan, MN
Based on an investigation from FOSS Kit Physics of Sound, copyright 2000
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Students will use a tongue depressor, xylophone, and kalimba to investigate how length affects pitch. They will record data in their Science Notebooks.

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Learning Goals

This activity is designed for students to see the relationship between length and pitch. Throughout the investigation, students will compare high-, low-, and medium-pitched sounds and compare the frequency of vibrations made by various sound sources producing different pitches. Vocabulary: vibration, pitch, xylophone, kalimba

Context for Use

The activity is designed for grade 3-4 and should take about 45 minutes. Prior to the investigation, students should understand that vibrations make sound. They should also know the difference between a sound source and a sound receiver. Students will work in pairs and have 10 minutes to work with each tool and record data.

Subject: Physics:Oscillations & Waves
Resource Type: Activities:Classroom Activity
Grade Level: Intermediate (3-5)

Description and Teaching Materials

Materials needed: 1 Tone generator for the teacher, tongue depressor and desk, xylophone (set of five xylophone tubes, mallet, and foam piece), Kalimba (Kalimba base, set of five flat steel springs, and craft sticks) for every four students, copy of Kalimba for each student to glue into Science Notebook. Materials will be shared among four students, but the investigation will be done in pairs.

Anticipatory Set:
Using a tone generator, have students stand on their tiptoes if the pitch is high and squat if the pitch is low. This will help students understand the difference between high- and low- pitched sounds. At this time, define pitch: how high or low a sound is. A connection to music and instruments could be made at this time.

1. Ask the investigable question, "How does length affect pitch?"
2. Ask students what tools they could use to find the relationship between length and pitch.
3. Show students the 3 different tools they will use: tongue depressor, xylophone (musical instrument made from a set of bars or tubes of different lengths), and kalimba (an African thumb instrument). Remind the class to respect the tools.
4. Explain to the class that they will work in pairs using each tool for 10 minutes. A bell will ring when it is time to switch tools. They will record their data and results in their Science Notebooks. If time permits, they can add other investigable questions they may have in their Notebooks.
5. Walk around the room to observe student understanding. Check drawings for any misconceptions.
6. Put materials aside for closure.

Ask again, "How does length affect pitch?" Listen to student findings and have them present their data to the class. Some students may show their data on the board or on the overhead projector. Ask, "What happens to the pitch and vibrations when the length of the sound source changes? Answer: A long object has a low pitch and vibrates slowly. A short object has a high pitch and vibrates quickly. Ask, "What are some musical instruments that make different pitches by changing the length of the sound source?" Answer: Trombone, recorder, harp, etc. Give students time to record additional information they learned from the closing discussion.

Teaching Notes and Tips

I like to have student jobs to keep order when distributing materials. I also think it is helpful to provide a copy of the kalimba drawing for students to glue in their Science Notebooks. It saves time and helps those who are easily frustrated with drawing.


Students will record data in their Science Notebooks as a formative assessment. They will explain in words how length affects pitch. Review drawings and explanations to determine student mastery. Also, walk around and listen to students as they work in pairs.


3.II.C.1 The student will investigate how sounds are made when objects vibrate.

References and Resources