Introduction to Mechanical Waves and Sound

Introduction

It is difficult to overstate the importance of understanding and predicting wave phenomena in our modern society. The energy contained in waves allows communications over vast distances beyond the outer reaches of our solar system and at the same time is responsible for the destruction of thousands of miles of coastline. Waves are everywhere, from the music we enjoy (both sound systems and musical instruments) to the destructive forces behind natural and man-made disasters. Our introduction to wave phenomena sets the stage for a deeper understanding of waves and wave interference that will enable our characterization and engineering of matter from the inner reaches of subatomic interaction to the outer reaches of our universe.

Essential Questions

What is the difference between a transverse wave and longitudinal wave?
Waves carry what from one location to another, and what is it that they do not carry?
What is the relationship among wavelength, frequency and speed of a wave?
What determines the pitch of a stretched string?
How do boundary conditions effect the reflection of a wave?
What is the generally accepted range of human hearing?
What characteristic of a wave is effected by either the source of a wave or an observer moving toward or away from each other?
Can you name five ways in which waves interfere?
What effect do boundary conditions have on harmonics for vibrating strings and columns of air?
How are beat notes used for musical instruments and radio communications?

Key Terms

Amplitude - a measure of the maximum change in a periodic variable, such as displacement velocity or acceleration, from an average value over one period
beat frequency - an interference between two sounds of slightly different frequencies, perceived as periodic variations in volume whose rate is the difference between the two frequencies.
Constructive interference - a phenomenon in which two waves of the same frequency superimpose to form a resultant wave of greater amplitude.
crest - the point on a wave with the maximum value or upward displacement within a cycle. A trough is the opposite of a crest.
Destructive interference - a phenomenon in which two waves of the same frequency superimpose to form a resultant wave of lower amplitude.
Doppler effect - The change in frequency of a wave for an observer moving relative to its source.
frequency - the number of occurrences of a repeating event per unit time.
fundamental - the lowest frequency of a periodic wave.
harmonic - component frequency of a complex wave that is an integer multiple of the fundamental frequency.
infrasonic - sound that is lower in frequency than 20 Hz (cycles per second), the generally accepted lower limit of human hearing.
Interference - a phenomenon in which two waves of the same frequency superimpose to form a resultant wave of greater or lower amplitude.
linear density - the measure of mass per unit of length.
longitudinal wave - waves whose direction of vibration is the same as their direction of travel.
node - a point along a standing wave where the wave has minimum amplitude.
period - the interval of time within which a periodic function repeats.
phase - the initial angle of a sinusoidal function at its origin.
pitch - characteristic of a sound wave established by its frequency
standing wave - an interference effect of two waves of the same frequency traveling in opposite directions and superimposing to produce a wave that remains in a constant position.
transverse wave - a wave in which the disturbance is perpendicular to the direction of the wave.
trough - the point on a wave with the minimum value or downward displacement within a cycle. A crest is the opposite of a trough.
ultrasonic - sound that is higher in frequency than 20,000 H2 (cycles per second), the generally
accepted upper limit of human hearing.
wavelength - spatial period of the wave the distance over which the wave's shape repeats.

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