Vibrations in a rubber sheet
Circular waves on a rubber sheet can produce a standing wave pattern.
Apparatus and materials
Retort stand bases and rods, 3
Boss and clamp
Aluminium ring, large
Rubber band (s)
Health & Safety and Technical notes
Draw radial lines on the rubber to make the oscillations easier to see.
Holding the sheet to the ring with a large rubber band makes it easy to make small adjustments to the evenness of the sheet’s tension.
The larger the power delivered by the loudspeaker, the better.
a Stretch the sheet over the large metal ring, as shown in the diagram. Make it as evenly stretched as possible.
b Place the large loudspeaker below the ring and rubber sheet.
c Drive the loudspeaker at frequencies in the range 10 to 100 Hz. Try a central position of the speaker first, and a low frequency. Raise the frequency gradually, looking and listening for the lowest mode, in which the centre of the rubber sheet rises and falls. The amplitude may be 10 to 20 mm at the centre.
At a higher frequency, with the speaker off centre, you can create a mode of oscillation in which the rubber surface tilts, one side rising as the other falls, the rim staying fixed of course.
This is similar to the experiment Ring of standing waves.
You may wish to link this demonstration to the wave-mechanical model of the atom, with electron waves fitting into the atom.
This experiment was safety-checked in February 2006