The 42nd Period | STEM Education Hub

Four quick experiments, all pointed at the same question: does what you measure match what you actually hear?

🎯 Goals

Test how a physical change (water level) affects pitch, and connect the result to frequency.
Measure real decibel levels and compare them to how loud those sounds actually feel.
Test the '+10 dB ≈ twice as loud' rule of thumb against your own hearing.
Estimate whether a described sound is audible, infrasound, or ultrasound, then check your guess.

🍾4–5 glass bottles or drinking glasses

💧Water and something to measure/pour it with

📱A phone with a decibel meter app (or readings provided by your teacher)

📓Physics notebook

Section 1 of 4

Line up 4–5 bottles or glasses with different water levels.

Before testing, predict: will more water make a higher pitch or a lower pitch when you blow across the top?

Blow gently across the top of each bottle and listen to the pitch.

Order the bottles from lowest pitch to highest pitch based on what you hear.

Connect your ordering to water level and to frequency.

Explain what's actually vibrating (hint: it isn't the water) and why changing the water level changes that vibration's frequency.

Section 2 of 4

Use a decibel meter app to measure 4–5 different classroom sounds (talking, a dropped book, silence, etc.).

Record the actual dB reading for each sound alongside your own 1–10 'how loud did that feel' rating.

Section 3 of 4

Find two of your measured sounds that differ by roughly 10 dB.

If none of your sounds happen to differ by close to 10 dB, measure one more sound until you find a pair that does.

Compare your 'felt loudness' ratings for that pair to the rule's prediction (about twice as loud).

Did your gut reaction roughly match the rule, or was it pretty different?

📓 Physics Notebook

Where did the +10 dB rule match your own hearing well, and where did it feel off? What might explain any mismatch?

Section 4 of 4

For each sound described below, guess whether it's audible to humans, infrasound, or ultrasound.

Make your best guess before checking any references — the guessing is the point.

A bass drum's low thump

A dog whistle

A bat's echolocation call

A typical human voice speaking

A truck's engine idling

Check your guesses against the Deep Dive's Hearing Range Explorer, and correct any you got wrong.

Note which ones surprised you most.

Question 1

Explain what's vibrating when you blow across a bottle, and why more water raises or lowers the pitch.

Question 2

Using your own decibel data, explain the difference between a sound's measured dB level and how loud it felt to you.

Question 3

Which frequency estimation surprised you the most, and why did your intuition miss it?

📤 Turn In