Sound is a Longitudinal Wave

Sound Sound is a Longitudinal Wave: The energy from the source of a sound is what travels to your ears, not the original particles that made the sound Basically, a density vs time graph is the same as a pressure vs time graph Sound waves only travel in space if there are enough particles around to transmit the energy in the wave from the source to the listener The speed of sound is 340 m/s Production of Sound: Remember, sound is simply the transfer of energy across particles in space that eventually get to your ear (disturbance of air) Waves can transport energy through a medium without transporting the medium itself Sound Properties: Amplitude, Period, Frequency, & Wavelength: If you increase amplitude, volume increases If the period (T) is decreased, then the frequency (f) increases, leading to a higher pitch (f = 1/T and is in units of 1/s, which is also known as a Hz) Humans can hear frequencies from 20 Hz to 20,000 Hz Speed of Sound: Transverse wave has particles that are displaced perpendicular to the direction the wave travels Longitudinal wave has particles that are displaced parallel to the direction the wave travels (i.e. sound) 𝑠𝑝𝑒𝑒𝑑 = 𝛌 " = 𝛌𝑓→ works for all kinds of waves, like those on the electromagnetic spectrum (increasing/decreasing wavelength/frequency won’t alter the speed of sound because the other variable will just compensate for the change) The only way to change the speed of sound is to alter the medium with which the sound is traveling in (i.e. you can also change temperature, humidity, density of air or change the composition of the air entirely) Changing amplitude of the sound wave ONLY changes the volume NOT its speed Relative Speed of Sounds in Solids, Liquids, & Gases: The stiffer the medium, the faster the sound wave will travel through it The denser the medium, the slower the sound wave will travel through it (i.e. hot air is fast vs cold air is slow) Speed of sound is almost always faster through solids, then liquids, and then gases Decibel Scale: The decibel scale tells you how loud something is with equation: 𝛽 = 10𝑙𝑜𝑔10 ( # 10!12 $/&2 ) where β is the # of decibels, I is the intensity of the soundwave (Power/Area), and the 10-12 W/m2 is the threshold of human hearing (the softest sound you can hear) Why do sounds get softer?: People closer to the speaker hear the sound as louder because of higher intensity (power/area) → area is a lot smaller than if you - - are farther from the speaker (your ear only measures a sample of the sound dispersed evenly throughout the area) Intensity is proportional to 1/r2 Also, as distance is covered, energy is lost and therefore the amplitude decreases over distance (AKA attenuation) Ultrasound Medical Imaging: Ultrasound has to do with frequencies above 20,000 Hz Ultrasounds use high f and low wavelengths because there is less diffraction (lower amount of waves spread out which would curve waves and confuse the transducer) → also since you can’t hear it, then the patient is more comfortable The lower the liquid in a tube is, the lower the pitch will be Doppler Effect Introduction: The Doppler Effect is an increase (or decrease) in the frequency of sound, light, or other waves as the source and observer move toward (or away from) each other. The effect causes the sudden change in pitch noticeable in a passing siren, as well as the redshift seen by astronomers Equations for source moving towards you → Equations for source moving away → Extra Notes: Inverse square law: intensityA/intensityB = (distanceB/distanceA)2