Science and Technology K–6 · Years 1–2
High or low: the length of a vibrating string changes its pitch
Physical World, energy comes in different forms that can be detected (NSW 2017); Science understanding, Physical sciences (ACARA v9)
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The idea
Shortening the part of a string that vibrates makes it vibrate faster and sound higher; halving the length raises the note by an octave.
What you need
- An open shoebox with three elastic bands of the same thickness stretched across it
- A pencil to slide under the bands as a movable bridge; a ruler
- A free tuner app on a tablet that reads the frequency of a plucked note in hertz
- Recording table: vibrating length (cm), reading (Hz), high or low by ear
How to do it
- Pluck one band with no bridge. Measure the vibrating length. Read the tuner and record the hertz.
- Predict what the reading will be at half the length.
- Slide the pencil bridge so the vibrating part is three-quarters of the length, then half, then a quarter. Pluck, listen and record each time.
- Pluck one band softly and then hard at the same length: does the pitch change or only the loudness.
- Compare with the class guitar or ukulele if there is one: press a string at the 12th fret, halfway along, and pluck.
What you should see
The shorter the vibrating part, the higher the note and the higher the tuner reading; at half the length the reading is close to double the open reading (one octave up). A rubber band stretched over a box is not a perfect string because the bridge also changes its tension a little, so the class gets near double, not exactly double; a guitar string pressed at the 12th fret halves the vibrating length and gives the doubling. Plucking harder makes the note louder, not higher. The learner knows it worked when the readings rise as the length is shortened and the half-length reading is about twice the open one.
What changes
- What you change
- vibrating length of the band
- What you measure
- pitch (tuner reading in Hz; high or low by ear)
- What you keep the same
- same band
- same pluck strength
- bridge pressed with the same weight
Common misconceptions
Each of these ideas is wrong, and the activity is a chance to test it.
- Plucking harder makes a higher note.
- A longer band makes a higher sound because there is more of it to vibrate.
Safety card
Hazards
- Elastic band snapping
Controls
- Bands not overstretched; eyes kept back when plucking
Note
No chemicals or heat. Record the activity on the school's risk assessment (Primary School RiskAssess, Ecosolve Australia, riskassess.com.au).
Curriculum references
The NSW syllabus outcomes and Australian Curriculum v9 codes this activity supports. They are references, not a verified or complete curriculum alignment.
- Science and Technology K-6 Syllabus (2017), NESA. Current syllabus; NESA's timeline is 2026 plan and prepare, 2027 start teaching the 2024 syllabus. Code read from the official syllabus document on 2026-09-22.ST1-8PW-SST1-1WS-S
- Science and Technology K-6 Syllabus (2024), NESA. Implementation from 2027, so this code describes the future syllabus. Code read from the outcomes page on 2026-09-22.ST1-SCI-01ST1-PQU-01ST1-DAT-01
- Australian Curriculum v9AC9S2U02AC9S2I01AC9S2I02AC9S2I03AC9S2I04AC9S2I05
Sources
The pages the author read to write this activity.