Ch 16: Waves & SoundSee all chapters
All Chapters
Ch 01: Units & Vectors
Ch 02: 1D Motion (Kinematics)
Ch 03: 2D Motion (Projectile Motion)
Ch 04: Intro to Forces (Dynamics)
Ch 05: Friction, Inclines, Systems
Ch 06: Centripetal Forces & Gravitation
Ch 07: Work & Energy
Ch 08: Conservation of Energy
Ch 09: Momentum & Impulse
Ch 10: Rotational Kinematics
Ch 11: Rotational Inertia & Energy
Ch 12: Torque & Rotational Dynamics
Ch 13: Rotational Equilibrium
Ch 14: Angular Momentum
Ch 15: Periodic Motion (NEW)
Ch 15: Periodic Motion (Oscillations)
Ch 16: Waves & Sound
Ch 17: Fluid Mechanics
Ch 18: Heat and Temperature
Ch 19: Kinetic Theory of Ideal Gasses
Ch 20: The First Law of Thermodynamics
Ch 21: The Second Law of Thermodynamics
Ch 22: Electric Force & Field; Gauss' Law
Ch 23: Electric Potential
Ch 24: Capacitors & Dielectrics
Ch 25: Resistors & DC Circuits
Ch 26: Magnetic Fields and Forces
Ch 27: Sources of Magnetic Field
Ch 28: Induction and Inductance
Ch 29: Alternating Current
Ch 30: Electromagnetic Waves
Ch 31: Geometric Optics
Ch 32: Wave Optics
Ch 34: Special Relativity
Ch 35: Particle-Wave Duality
Ch 36: Atomic Structure
Ch 37: Nuclear Physics
Ch 38: Quantum Mechanics

The Doppler Effect

See all sections
What is a Wave?
The Mathematical Description of a Wave
Waves on a String
Wave Interference
Standing Waves
Sound Waves
Standing Sound Waves
Sound Intensity
The Doppler Effect

Concept #1: The Doppler Effect

Practice: A police siren emits a sound somewhere around 700 Hz. If you are waiting at a red light, and a police car approaches you from behind and passes you, moving at a constant 30 m/s, what is the frequency you hear from the siren as it approaches you from behind? What about once it’s passed you? Assume the air temperature to be 20°C.

Example #1: Two Submarines Approaching One Another

Additional Problems
An object emitting a sound at a constant frequency is thrown into the air. As the source travels up and back down again, the frequency you hear is going to change via the Doppler effect. Assuming the source is always above your ear, which of the following statements if true: (a) The frequency heard will start at a maximum and decrease through the entire trip (b) The frequency heard will start at some value, decrease to a minimum value as it rises, and then increase back to its starting value as it falls (c) The frequency heard will start at some value, increase to some maximum value as it rises, and then decrease back to its starting value as it falls (d) The frequency heard will start at a minimum and increase through the entire trip
Two speakers, A and B, are moving towards each other with a closing speed of 30 m/s, meaning the distance separating the two speakers is decreasing by 30 m every second. At rest, speaker A emits a frequency of 150 Hz and speaker B emits a frequency of 200 Hz. For all questions, assume the speed of sound is 340 m/s. (a) From speaker A's perspective, what is the frequency of speaker B? (b) From speaker B's perspective, what is the frequency of speaker A? (c) If an observer were standing in between the two speakers, and speaker A were moving towards him with a speed of 10 m/s, what beat frequency would the observer hear?
A police car is traveling at a speed vc to the right and a truck is traveling at a speed  vt to the right. The frequency of the siren on the police car is fc.  What is the frequency ft heard by an observer in the moving truck? Let  vt be the speed of the observer in the truck, and vc be the speed of the source, the police car. The speed of sound in air is va.
An ambulance is traveling North at 54.3 m/s, approaching a car that is also traveling North at 33.6 m/s. The ambulance driver hears his siren at a frequency of 678 cycles/s. The velocity of sound is 343 m/s. At what frequency does the driver of the car hear the ambulance's siren?