Sound Waves

The waves will move in a straight line parallel to the energy that first moved the particles. No matter what the source of the sound wave is, all sound will be a longitudinal wave because it always moves in a direction parallel to the direction of energy transport. (Ludwig).
             These longitudinal waves can also sometimes be referred to as pressure waves. (Huffstetler) The idea behind a pressure wave is that when energy is moving through a medium, the particles that are vibrating alternate between areas of high and low pressure. The high-pressure sections of sound waves are call compressions because the particles in the section are pushed together. The low-pressure sections of sound waves are called rarefactions because the particles in the section are spread apart. (Huffstetler) These compressions and rarefactions make a sound wave pulsate through the air at different air pressures in a certain direction. (Russell).
             Sound waves, regardless of what medium or disturbance creates it, are all composed of frequencies and pitches. The frequency of a sound wave is how often that the particles in the medium are vibrated in a given wavelength. (Henderson) The frequencies are measured in Hertz (Hz). They are defined as the number of complete back-and-forth vibrations of a particle of the medium per unit of time. (Ludwig) 1 Hertz would equal 1 vibration per second and would be an extremely low pitch bass note, impossible to hear by the human ear. A note this low is called an infrasound wave because it is too low to be heard by most animals. Infrasound waves are anything lower than about 20 Hz. Just oppositely, a frequency that is too high is called an ultrasound wave. These waves are anything above about 20,000 Hz. The human ear can detect any frequency between 20 and 20,000 Hz, but there are some animals that can hear lower and higher frequencies. For example, an elephant can detect an infrasound wave as low as 5 Hz and a dolphin can detect an ultrasound wave as high as 200,000 Hz.