# Read sound-wave diagrams in ManYue: check axes before amplitude and frequency

Language: en
Canonical: [Read sound-wave diagrams in ManYue: check axes before amplitude and frequency](<https://allluckly.cn/en/guides/manyue-sound-wave-longitudinal-pressure-axis/>)
中文：[中文 HTML](<https://allluckly.cn/guides/manyue-sound-wave-longitudinal-pressure-axis/>)
English: [English HTML](<https://allluckly.cn/en/guides/manyue-sound-wave-longitudinal-pressure-axis/>)
Published: 2026-11-14T00:00:00+08:00
Modified: 2026-11-14T09:31:46+08:00
Author: Bison

Compare air compressions, pressure-versus-position and pressure-versus-time plots, calculating wavelength and period while separating particle motion from propagation.

English translation of the [Chinese original](<https://allluckly.cn/guides/manyue-sound-wave-longitudinal-pressure-axis/>), translated on 2026-11-14. Original publication dates, attribution, code and version notes are retained.

An up-and-down sound curve does not mean air particles travel along that drawn path. Read three original diagrams in ManYue, checking axes before relating compressions, rarefactions, period and wavelength. This is a paper model without loud sources or instrument measurements. The reader calculates and interprets; a comic curve is not an app-generated audio analysis.

## Record all three diagrams and axes

A uses dots for air density and a rightward propagation arrow. B plots pressure relative to equilibrium against position in metres at one instant. C plots pressure against time in seconds at one fixed location. Name diagrams, time and position conditions and record source markers. Similar sinusoidal shapes do not make B and C interchangeable: the horizontal axis determines wavelength versus period. All values are teaching assumptions, not field measurements.

## Separate particles from the disturbance

Mark two compressions and an intervening rarefaction in A, then identify one dot oscillating near its equilibrium position while the disturbance travels rightward. In ordinary longitudinal airborne sound, particle oscillation is parallel to propagation; the air mass is not transported rightward at sound speed. This simplified diagram does not measure omitted three-dimensional or thermal motion. If arrows lack a legend, distinguish propagation from particle displacement before interpreting them.

## Do not treat pressure height as a trajectory

B’s vertical height describes pressure deviation, not a particle’s vertical coordinate. A positive pressure peak can correspond to compression and a negative trough to rarefaction. Match one peak to A’s compressed region rather than label airborne sound transverse because the graph rises and falls. A displacement graph requires a different mapping, so do not transfer pressure-peak rules to it. Read quantity names before shapes; absent axis labels limit interpretation.

## Read wavelength from position before frequency

Let adjacent in-phase pressure peaks in B be point eight five metres apart: that is the model wavelength. With an assumed speed of three hundred forty metres per second, not a universal environmental constant, divide to obtain four hundred hertz. A peak-to-trough half-wavelength would incorrectly yield eight hundred. Track metre and metre-per-second units to obtain cycles per second. Calculate manually, without app peak extraction or measuring screen centimetres as physical metres when no scale supports it.

## Read period from time and cross-check

At one location C’s consecutive in-phase peaks are point zero zero two five seconds apart, the period. Its reciprocal is four hundred hertz, agreeing with B. Period is time per cycle and frequency cycles per time; two point five milliseconds is not two point five hertz. Divide milliseconds by one thousand before taking the reciprocal and retain both steps. Mismatches call for checking model identity, units and half-period errors before changing speed assumptions. Phase origins may differ; peaks need not start at time zero.

## Change amplitude without changing frequency

Make D with C’s horizontal axis and peak spacing but twice the pressure amplitude; taller does not automatically mean higher pitch. In a simple pure-tone model frequency relates to pitch and pressure amplitude to strength, while perceived loudness also depends on frequency, duration and hearing. This exercise calculates no decibels and assesses no hearing. Separate amplitude from spacing and check vertical scales, since automatic plot rescaling can hide or mimic a physical amplitude ratio.

## Check axis errors and trajectory confusion

If B’s point eight five becomes seconds, restore its position-in-metres axis. If particles climb drawn peaks, return to A’s oscillating dot and propagation arrow. Check matching phases and whole cycles before calculating; denser lines alone do not mean louder sound. Without a speed, state a relation rather than invent room temperature. Static comics and large sound-effect lettering cannot establish pressure or safe distances. Share original diagrams and units, not recordings of private conversations.

## Reopen and reconstruct the model with units

Reopen the page and identify A through D before explaining particle motion, spatial wavelength, temporal period and amplitude control. Retain point eight five metres, three hundred forty metres per second, four hundred hertz and two point five milliseconds as an assumed-model chain. Explain why graph height is not air height. Recheck axes after medium, speed or coordinate changes instead of treating these values as universal. A bookmark locates the page without establishing an actual sound measurement.

## Related guides and sources

[ManYue heatmaps in pictures: identify rows, columns and colour ranges before comparing cells](<https://allluckly.cn/en/guides/manyue-in-story-heatmap-cell-bin-legend/>); [ManYue motion-symbol reading: separate speed lines, arrows and object paths](<https://allluckly.cn/en/guides/manyue-motion-symbol-path-reading/>).

Checked on November 14, 2026: [Apple public information](<https://itunes.apple.com/lookup?id=6753895889&country=cn&entity=software&timestamp=20261114>) lists ManYue 2.0.5, requiring iOS / iPadOS 15.0 or later. See the [official App Store](<https://apps.apple.com/cn/app/id6753895889>) for published capabilities; verify specific controls in the installed version.

Method reference: [OpenStax: speed, frequency and wavelength of sound](<https://openstax.org/books/physics/pages/14-1-speed-of-sound-frequency-and-wavelength>). Samples, passages and controls are original exercises. Sources establish definitions and checking methods rather than new automatic analysis in the app. Manual records may be kept externally, and unknown fields should remain explicit. This article does not claim step-by-step testing on a physical device, private server or every output environment.