Doppler Effect & Shock Waves

Doppler Effect When a wave source is traveling with respect to an observer, the observer perceives a difference in frequency of the waves This can be accomplished with a moving wave source or with a moving observer

Doppler Effect & Sound If a moving sound source is coming toward you, the wave fronts are bunched together, so the wavelengths are shorter and you perceive a higher frequency or pitch If a moving sound source is traveling away form you, the wave fronts are spread apart, so the wavelengths are longer and you perceive a lower frequency or pitch

Example You are driving toward a parked emergency vehicle with its sirens on As you approach the vehicle, the sound you hear will be… Why? As you drive away from the vehicle, the sound you hear will be… Why?

Doppler Effect & Sound Is the sound frequency actually changing? Is the wave speed changing?

Shock Waves When the speed of the moving source is equal to or greater than the speed of the waves, a shock wave is produced

Shock Waves A shock wave produces a cone shape When the source is moving faster than the wave speed, all of the wave fronts are behind the source

Sonic Boom When a source producing sound waves travels faster than the speed of sound, the overlapping sound waves in the cone create regions of alternating very high and very low pressure which all reach the observer at one time, creating a loud boom NOT only heard when speed of sound is reached, but anytime the shockwave cone reaches your ear.