Vibration — Science definition

Repeated motion around a rest position.

Where it is taught

In use

Students who cannot hear a sound can study its visible motion and supplied vibration records.

Sound Sources, Vibrations & Receivers

Questions using vibration

Problem 1

OpenSciEd graph B of source position in millimetres against time from 0 to 0.01 seconds, showing repeated vibrations around a mean position of about 20 millimetres.
OpenSciEd 8.2 Sound Waves, Lesson 5: actual position-versus-time record B. Read the labeled axes and estimate a cycle interval before opening the worked guidance. The vertical value is the vibrating point’s position relative to a coordinate origin, not air pressure or sound wavelength. Sound-source vibration graph B · OpenSciEd · 8.2 Sound Waves, Lesson 5, source, CC BY 4.0. Figure excerpt rendered from the PDF and resized for the web.
Read OpenSciEd record B. Estimate its period, frequency and amplitude. Compare it with record A, whose frequency is about 300 Hz and amplitude about 0.8 mm. Which vibration property has changed by a factor of two, and which has stayed approximately the same?
Answer and explanation

One cycle takes about 0.0017 s, giving frequency about 600 Hz using cycles per second = 1/period. The midline is near 20 mm and extrema are about 19.2 and 20.8 mm, so displacement amplitude is about 0.8 mm. Amplitude measures departure from the midline, not distance from the coordinate origin. Allow reasonable approximate readings from this source graph. B has about twice A’s frequency and half its period, while displacement amplitude stays approximately 0.8 mm. Faster repetition does not automatically mean a larger vibration.

Compare consecutive peaks: about 0.0017 s per cycle.

Compute 1/period, approximately 600 cycles per second, or Hz.

Amplitude is about 20.8−20 = 0.8 mm (half the peak-to-peak displacement).

Response criteria

  • Read time on the horizontal axis; do not call it wavelength.
  • Estimate frequency from repeats per second.
  • Measure amplitude from the midline and distinguish coordinate origin from equilibrium.

Taught alongside

Elsewhere

Browse all courses