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
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
Beats

Concept #1: Beats

Practice: A string emits an unknown sound. You strike a tuning fork which emits a sound at EXACTLY 300 Hz, and you hear a beat frequency of 20 Hz. You then tighten the string, increasing the tension in string. After you pluck the string and strike the tuning fork, you hear a new beat frequency of 30 Hz. What is the unknown frequency of the string, originally?

Additional Problems
Sound at 50 kHz can be used by police to measure a car's speed in a speed trap. If a car is travel at a speed relative to the source of the sound, a beat frequency will be produced when the sound returns to the source. The fast the car is moving, the larger the beat frequency produced. If the speed limit in a neighborhood is 40 mph, what is the largest beat frequency produced by a car still traveling at the speed limit? Assume that the speed trap is set up to bounce sound waves off the back of a car as it is driving directly away from the source of sound.
A train whistle produces a sine wave with a wavelength of 0.7841 m in air when the speed of sound is 345 m/s. As the train is approaching you from far away, you are standing near the track when you hear a sound with a frequency of 523.25 Hz. (a) What is the train's speed relative to you? (b) What frequency do you hear after the train passes you? (c) A second identical train is trying to catch up to the first. After it passes you, it blows its whistle at the same time as the first train is blowits whistle, causing you to hear a beat frequency of 10.0 Hz. What is/are the speed(s) of the second train relative to you?
A speaker near you is emitting a sound at an unknown frequency. In order to discover the frequency, you use a tuning fork to emit a sound of 300 Hz, causing you to hear a beat frequency of 50 Hz.  (a) What are the possible frequencies of the speaker? (b) If you use second tuning fork at a frequency of 320 Hz, and you measure a second beat frequency of 70 Hz, what must the frequency of the speaker be?
A speaker on the edge of a well emits a sound at 500 Hz when it's accidently knocked over and falls into the well. As the speaker is falling, sound is being emitted downwards and reflected off the bottom of the well, traveling back upwards towards the speaker and producing beats. After the speaker has fallen some distance, it is moving at 10 m/s. What is the beat frequency created by the interfering sound waves at this point in time? Assume the speed of sound is 340 m/s.
Two organ pipes are played at one, both at their harmonic frequencies. If one pipe is closed at one end and the other is open at both ends, and both pipes are 0.8 m long, what is the beat frequency you'd hear from the pipes?
When a tuning fork of frequency 565 Hz vibrates beside a piano string, beats are heard. The string is loosened slightly and the beats go away. What was the original frequency of the string? A. 565 Hz B. greater than 565 Hz C. less than 565 Hz
In certain ranges of a piano keyboard, more than one string is tuned to the same note to provide greater intensity. For example, the note at 151 Hz has two strings at this pitch. If one string slips from its normal tension of 637 N to 521 N, what beat frequency will be heard when the two strings are struck simultaneously?
Two strings both vibrate at exactly 819 Hz. The tension in one of them is then increased slightly. As a result, six beats per second are heard when both strings vibrate. What is the new frequency of the string that was tightened?A) 825 HzB) 813 HzC) 822 HzD) 816 Hz
An acoustic burglar alarm consists of a source emitting waves of frequency 28.50 kHz. An intruder is walking at an average speed of 0.9600 m/s directly away from the alarm. Take the speed of sound to be 343.0 m/s.(a) What is the wave length of the source waves?(b) What is the frequency and wavelength for the intruder? The waves are reflected by the intruder and back to the alarm system.(c) What is the frequency and wavelength for the waves reflected from the intruder, as detected at the source?(d) What is the beat frequency between the source waves and the waves reflected from the intruder?