I'm not clear which person wrote that sound is not a vibration, but that is incorrect. The air molecules do move through cycles in harmonic motion, passing through a central point of equilibrium. Sound is not just pressure only - it alternates between positive and negative pressure, forming the positive and negative portions of the wave, whether sine wave or complex sound wave. Waves on water are a good 2 dimensional representation of what happens in 3 dimensions in the air. The waves travel out from a central point, but the water molecules move up and down in harmonic motion. A floating leaf on a still pond will demonstrate this nicely. Don Mannino _____ From: caut-bounces at ptg.org [mailto:caut-bounces at ptg.org] On Behalf Of Keith Roberts Sent: Wednesday, May 13, 2009 7:02 AM To: caut at ptg.org Subject: Re: [CAUT] Semantics Correct me if I'm wrong but wouldn't a longintudinal wave be a sound type of wave, only in a different medium? It has speed that can be measured and reflects off of things. When something vibrates it is because it is under tension and fixed with a flexible center or end so it wants to return to center. This can happen on a cellular or fiber level as in a block of wood. Keith Roberts On Wed, May 13, 2009 at 6:11 AM, Keith Roberts <keithspiano at gmail.com> wrote: On Tue, May 12, 2009 at 10:21 AM, <afmamh7 at bellsouth.net> wrote: I am not an acoustician, but I think it is incorrect to consider sound and vibration as two different types of energy. Sound IS vibration. Sound is not vibration. Sound is an impulse that is a wave of air. It leaves from it's point of origin and never goes back unless acted upon by another force. It is confusing that it does have frequency and amplitude. Take the wave pattern caused by dropping a rock in a pond. The resultant waves have direction, amplitude and frequency but we don't call it vibration. Sound originates from a point source and disperses in the same manner as the water waves do. In vibration, the energy returns and crosses the center line of origin. Back and forth motion is vibration. Keith Roberts -------------- next part -------------- An HTML attachment was scrubbed... URL: <http://ptg.org/pipermail/caut.php/attachments/20090513/1599c395/attachment.htm>
This PTG archive page provided courtesy of Moy Piano Service, LLC