Wave Motion and Sound.rev

Wave Motion and Sound.rev - WAVE MOTION AND SOUND The...

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Part 2 WAVE MOTION AND SOUND The general discussion of wave motion is important because the ideas of wave propagation are ubiquitous. In nearly all areas of science (and therefore real life) energy is transferred via the vibrations that make up waves. Examples of wave motion include waves on strings, water waves, seismic waves,, sound, all electromagnetic radiation including light, heat, x-rays, etc. There are many common elements to all the various types of wave motion that can be described - and these will be pointed out. There are also some differences - especially between the mechanical waves such as waves on strings and sound and all electromagnetic waves - which will be important in some discussions. What is common to all forms of wave motion is the idea that a disturbance is being propagated from one place to another without the necessity for the medium through which the disturbance is being propagated to itself be transported. (We will see what that means shortly.) It is useful to first classify wave motion into several different categories. Already mentioned are mechanical waves and electromagnetic waves. This discussion will only deal with mechanical waves (although many of the important ideas also apply to electromagnetic waves). Mechanical waves can be either longitudinal or transverse . The distinction will be whether the disturbance that is being propagated is in the direction of travel of the wave or perpendicular to it. Longitudinal Waves: When a wave propagates through some medium, if the local displacements of the medium that constitute the disturbance are in the direction of travel of the disturbance, then the wave is l ongitudinal . An example of a longitudinal wave is the pulse that can be sent along a stretched slinky by shaking one end of the slinky along its length. The pulse moves along the line of the slinky and ultimately makes the other end move. Notice that in this case, the individual coils of the slinky vibrate back and forth about some equilibrium position, but there is no net movement of the slinky itself. You can think of the slinky as the medium through which the pulse travels - and the wave motion describes the disturbance rather than the slinky. Examples of longitudinal waves are sound waves through the air or compression waves through some solid object. Transverse Waves: A disturbance that is perpendicular to the direction of travel are called transverse waves. Examples are waves on strings, surface waves on the water, etc. That is, the wave itself travels along the string or water surface - but displacements of the medium through which the wave travels are perpendicular to the direction of the wave propagation. In both cases (and in all other forms of wave motion), the disturbance moves through the medium (slinky, string, water, air, whatever. ...) with only a minimal motion of the medium itself. What is being described in the equations of wave motion is the motion of the disturbance. The wave speed , for example, is the speed at which the disturbance moves.
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This note was uploaded on 10/15/2009 for the course PHYS 132 taught by Professor Sharpe during the Winter '08 term at Cal Poly.

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Wave Motion and Sound.rev - WAVE MOTION AND SOUND The...

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