Mechanical+Waves-Sound

= Mechanical Waves/Sound =

Sound is transported by means of longitudinal waves through air and various materials. Generally, the speed of sound rises as the temperature of air rises. When sound traveles at 343 m/s, the temperature is 20 degrees Celcius.

Frequency plays an integral role in determining the pitch (how high or low) of a sound: as frequency increases, so does pitch. Humans can hear pitches ranging from 20 Hz to 20,000 Hz (1 Hz - 1 cycle per second).

The intensity of a sound wave basically refers to how loud it is, something that is determined by the amplitude squared of the wave. Sound levels can be figured out using logarithms. The sound level beta, in decibels, is defined in terms of intensity:

B = 10log (I / Io)

Io is usually 10 ^-12 W/m2

Fundamental frequency is the frequency from which sound occurs (like when you strike a guitar string and it produces sound). The fundamental frequency equates to a wavelength that is twice the length of the string ( wavelength = 2L). Higher frequencies that strings vibrate at are identified as overtones, or harmonics, where one or more additional nodes exist. Each harmonic has a whole-number multiple of the fundamental for a frequency.

For wind instruments, sound vibrates through an open tube, with displacement antinodes at each end. The fundamental frequency equates to the wavelength that is twice the tube length (same as guitar string one). For a closed tube (where one end is closed), the fundamental corresponds to a wavelength four times the length of the tube.

When sound waves are produced from different sources, they interfere. When the sounds have different frequencies, beats happen at a frequency that is equal to the differenc in frequency of the two sources.

The change in the pitch of sound due to the motion of a source or the listener is known as the Doppeler Effect. When the source and listener approach each other, the pitch is higher; when the source and listener move away from each other, the pitch drops;

Need to spin these.....