Sound Wave Exam

Pitch

• How high or low we perceive a sound to be, depending on the frequency of the sound wave

• “highness” or “lowness” of a sound

  – Corresponds to a sound’s frequency

  • Factors that affect Pitch:

  – Tension of string

  – Length of string

  • Short string = higher pitch

  • Long strings = lower pitch

  – Mass of string

  • If increase Tension, Pitch gets higher (increase in f)

  • If increase Length, Pitch gets lower (decrease in f)

  • If increase mass, pitch gets lower (decrease in f)

The speed of sound depends on:

• Medium

• Temperature

How are frequency and period related in simple harmonic motion?

• Inversely

In pendulums, Period depends on:

• Length

• Gravity

The lowest possible frequency of a standing wave is called ______ and occurs when n=1

• Fundamental Frequency

A sound wave moving through a liquid or gas is an example of a ____ wave, where the particle motion is ____to wave propagation

• Compressional

• Parallel

Simple Harmonic Motion:

• The back and forth, repeating motion

Frequency (f):

• The number of oscillations (cycles) per second

• f=# of cycles/seconds

• Units: Hz

• Inverse of period: f= 1/T

Period (T):

• The amount of time it takes to complete one oscillation (cycle)

• A cycle is one complete back and forth trip

• Units: seconds (s)

• Inverse of frequency T= 1/f

Amplitude (A):

• The magnitude of maximum displacement from equilibrium point

• Equilibrium point is resting point (location where no force is applied)

• How much energy there is.

• In a pendulum, it is measured in degrees.

• In a spring, it is measured in meters

Wavelength(λ):

• The distance between two identical points on a wave

• Represents one oscillations (cycle)

• Units:Meters

Pendulum:

• Period (T) depends on the length of oscillation due to gravity

• Does NOT depend on Mass (m) or Amplitude (A)

Spring

• Period (T) depends on Mass (m) and the Spring Constant (k)

• Does not depend on Amplitude (A)

Two types of waves:

• Transverse

• Compressional/Longitudinal

Waves transfer ____, not matter

• ENERGY

Sound Waves are:

• Compressional/Longitudinal waves

Light waves are:

• Transverse waves

Transverse Waves:

• Particles vibrate perpendicular to the direction of energy transfer

Compressional/Longitudianl Waves:

• Particles vibrate parallel to the direction of energy transfer

As temp increases, speed of sound:

• increases (especially in gases)

Sound travels best in solids because:

• particles are closer together

Waves:

• Transfer of energy, not matter (the motion of a disturbance through a medium)

Medium:

• a physical environment that a disturbance can travel through.

Pulse Wave:

• When a person flips a string and generates a wave

Standing Wave:

• the resultant wave pattern appearing to be stationary on a string.

– Appears to be at a constant position

– Two waves with the same f, λ, and A, travelling through a medium in opposite directions.

Wave Interference:

when multiple waves pass through the same point of a medium. Two waves cross over one another, creating a single different wave. (When merge, create constructive interference)

Constructive Interference:

• When the disturbance of the medium of two waves is in the same direction leading to a larger “resultant wave”

• Waves “add” together to produce a larger wave

• Matter can’t share space with more matter.

• Energy waves can occupy the same space.

• Destructive Interference:

• When displacement of two waves are in opposite directions leading to a smaller “resultant” wave

Antinode:

• Max energy and Displacement

Node:

• No energy, zero displacement

There will always be ___ more node than antinodes.

• 1

Fundamental Frequency:

• The lowest possible frequency of a standing wave

• n = number of antinodes = harmonic number

• When n = 1, have First Harmonic

Harmonics:

• Multiples of fundamental frequency

Overtones:

• Harmonics heard on top of the fundamental

  frequency

  – Gives instruments their sound quality or “timbre”

  – For Strings, Overtone = (n – 1)

Resonance:

• when one object vibrates at the same natural frequency as a second object, forcing the second object into vibrational motion.

• ex. breaking a glass by voice

Frequency in Pipes:

• Air is what is vibrating

An open pipe has:

• two open ends

• Always have an antinode at the open ends of a pipe.

• Fundamental frequency is ½ of a wave

Closed Pipes:

• Pipe with one open end and one closed end.

• Antinode at open end

• Node at closed end

• Fundamental Frequency is ¼ of a wave, but you still add ½ of a wave with each harmonic.

• ONLY HAVE ODD-NUMBERED HARMONICS!

Compressions (air):

• areas of high pressure/density

Rarefactions (air):

• areas of low pressure/density

Echo:

• Reflected sound wave

Reflection:

-“bouncing” back of waves off a surface

Refraction:

• “Bending” of waves due to a change in medium

Diffraction:

• “bending” of waves due to obstacles

Beats:

• Provided by superposition of two sounds that are not at the same frequency.

Doppler Effect:

• The apparent change in the frequency of a sound caused by the relative motion between the source of the sound and the observer

• A moving sound source will sound higher (High Pitch = High frequency) as it approaches the listener.

• A lower sound (low pitch = low frequency) will occur as it moves away from the listener.

• Waves in front of the moving object “bunch” or “compress” while waves behind the object “spread out” or “elongate”.

• Occurs with all types of waves.

Sonic Booms:

• If the velocity of the sound source is faster than the speed of sound in the medium, it creates a shock wave called a “sonic boom”

• ex. cracking a wip