The Standing Wave

Physical Science began to revisit the concept of standing waves today during their discussion of sound. Friday's lab was a good exploration of how the speed of sound can be measured using a pipe closed on one end and how the identity of the medium affects the sound's speed. If you could actually see the sound in the pipe, you would see that it formed a standing wave, as one would find for a wind-based musical instrument. We'll delve into this deeper tomorrow when we discuss musical instruments and harmonics.

Physics and Honors Physics concluded their general survey of the properties of vibrations and waves. Honors Physics got to see first-hand how difficult it is to form standing waves and Physics will have this pleasure tomorrow. The requirement that a specific frequency be generated and maintained for standing wave formation is a hard one to satisfy with the human arm. We'll look at these in more detail when we cover sound in the next chapter. Gather up any and all questions for your exam review periods so that we can address any issues at that time for this week's test.

Not all standing waves form on strings. Air columns can vibrate and form standing waves and so can 2-dimensional planes, like the surface of a vibrating drum head. Ernst Chladni investigated this type of standing wave formation and found that lovely patterns were formed that could be seen by scattering small particles over the vibrating surface. For Chladni figures, the empty spaces represent areas of maximum displacement and the lines are areas where the displacement is cancelled out. For surfaces like a vibrating platform, antinodes are not necessarily loop-like in appearance and nodes appear as curves rather than points. Here's a video of Chladni figure formation. Note: playing this video with the sound on and a dog in the room will make for one weirded-out dog...