SCIENCE · GRADES 9-12 · 35-45 MIN
The Inverse Square Foot: Applied Physics & Acoustics lesson plan
Students measure sound level at doubling distances from a steady source and find the pattern in their data.
At a glance
Time: 35-45 min
Grades: Grades 9-12
Subject: Science: Applied Physics & Acoustics
Grouping: Teams of 3.
Space: A straight 24-ft line in an open space; real walls for the comparison round.
Teacher prep: 15 min printing + 15 min taping
Included: Teacher guide, student sheet, checks for understanding, exit ticket with answers
Open the printable lesson: teacher guide and student sheet →
Essential question
How does the loudness of a sound change as you move away from it — and what does a wall do to that pattern?
What students learn and show
Learn: Outdoors or in a large open space, sound level falls about 6 dB each time distance doubles; reflections and barriers change this.
Show: Plot level vs distance and describe the doubling pattern using their own readings.
Objectives
Measure sound level at doubling distances from a steady source
Describe how sound level falls with distance (about 6 dB per doubling in open space)
Compare open-space readings with readings through a real doorway or wall
Apply the finding to a design decision
Before this lesson students should: Plotting points; doubling; the idea that decibels are a logarithmic scale (brief teacher explanation is enough).
Materials and prep
The 1:1 print
One phone per team with a free decibel-meter app
One constant sound source (a phone playing a steady tone)
Tape measures
Clipboards
Prep (about 15 min to print, 15 min to tape)
Choose a large open area, preferably outdoors, away from walls.
Mark stations at 3, 6, 12 and 24 ft from the source with tape.
Test the decibel app and the steady tone; set the source volume and do not change it.
Space: A straight 24-ft line in an open space; real walls for the comparison round.
Grouping: Teams of 3.
Ways to run it: Painter's tape on the floor; 1:1 printed floor plan; real
Lesson procedure
Teacher model: Teacher reads the meter at 3 ft and at 6 ft, holding the phone at the same height. 'From 3 to 6 ft the level dropped about 6 dB. Predict the reading at 12 ft.'
Guided practice: All teams take the 3-ft and 6-ft readings, then predict 12 and 24 ft before measuring.
Place the steady sound source at one end of a straight line in an open area; mark it with tape.
Teams record the level at 3, 6, 12 and 24 ft, holding the phone at the same height and waiting for a steady reading.
Plot level vs distance. Does each doubling of distance drop the level by about the same amount? Name the pattern (about 6 dB per doubling outdoors).
Comparison: repeat two distances through a REAL doorway or around a real wall. A printed wall line does not block sound.
Debrief: why do architects care where the mechanical room goes? Students point to the answer on the plan.
Checks for understanding
Ask: If you double your distance from the source, about how much does the level drop outdoors? Look for: About 6 dB (the sound intensity falls to one quarter).
Ask: Why measure at the same height each time? Look for: Fair test: only the distance should change.
Ask: Does a printed wall line on the floor block sound? Look for: No. Only a real wall or barrier does. Use a real doorway for the wall comparison.
Exit ticket
Your readings: 3 ft = 80 dB, 6 ft = 74 dB. Predict 12 ft and 24 ft. Answer: About 68 dB and 62 dB.
Your indoor readings dropped less than 6 dB per doubling. Give a reason. Answer: Reflections from walls, floor and ceiling add sound energy; the room is not open space.
Scoring: Item 1: 2 points. Item 2: 1 point. Plot with labeled axes: 1 point. 3-4 secure.
Common misconception
Students may think: Sound drops by the same number of dB for every foot.
Address it: Look at your data: the drop is about the same for each DOUBLING of distance, not for each foot.
Supports and extensions
Learning support: Provide pre-marked measuring stations and a fill-in data table; assign the recording role.
Multilingual learners: Anchor chart pairing 'louder / quieter, closer / farther' with arrows before starting.
Mobility and access: Students can hold the meter from a seat while a partner moves the source, or read values from a shared data set. Data analysis stays the target.
Extension: Test a soft surface (jacket over the phone) as a crude sound barrier. Challenge: recommend the quietest room on the plan for a home office and defend it with data.
Transfer task: Where should a quiet reading corner go in the classroom, relative to the door? Use the doubling rule.
Spaced review: Two weeks later: 'A speaker reads 90 dB at 2 m. Estimate the level at 8 m outdoors.' (about 78 dB)
Standards connections
CCSS MP4 (domain-level practice)
NGSS HS-PS4 (domain-level practice)
Connections show which skills the activity practices. They are not a claim of full coverage; see the library for scope notes.
Why this approach
A National Academies consensus report arguing that spatial thinking is a teachable, underrecognized skill that belongs across the K-12 curriculum. Limit: A policy and synthesis report, not an experiment. It does not test this lesson.
Ready to teach it?
The printable version has the full teacher guide, a student recording sheet, prep steps and an exit ticket. Open the printable lesson →
Need the floor plan itself? Get a 1:1 print quote.
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