L1 - Properties Of Sound Flashcards
To hear sound you need ….
1….
2…
- A source (vibration)
- A medium (air,solid,liquid)
What is the best medium for sound to travel through and why?
solid (tightly packed molecules/dense so they can transfer energy easily = efficient for sound transmission)
Why are liquids and gases not the best medium for sound to travel?
liquid (closely linked, travels easily but lose energy over distance)
gas (molecules have lots of energy but further to travel)
Why can sound not travel through a vacuum ?
Sound cannot travel through a vacuum as there are no particles present for vibrations to take place.
What is the speed of sound (approx)
Approx. 340m/sec
What factors can affect the speed at which sound will travel and why?
Density in atmosphere (more dense = quicker)
Heat in atmosphere (more kinetic energy)
Define sound wave
A wave can be described as a disturbance that travels through a medium from one location to
another location.
Sound wave is always made up of
Backwards and forward motion of particles, the particles moving forward will encounter particles moving back – densely packed.
causing a wave of positive and neg pressure.
Sound Wave is always made up of:
• Areas of positive pressure (particles moving closer) = compression
• Areas of negative pressure (particles moving further apart) = rarefaction
Describe the tuning fork example
Strike tuning fork -→ fork vibrates back and forth -→back and forth displacement of vibrations, each particle will vibrate, then reaches detector (ear)
2 types of wave motion
- Transverse wave (water/ light) – wave is travelling perpendicular to source/particle
(source/particle up and down, wave forwards/right) - Longitudinal wave (Sound) – wave is travelling parallel to source/particle – direction of wave is in the same direction to the movement of molecules (source/particle and wave both moving forwards and back)
How to measure a wavelength and the units ?
peak -→ peak
• trough → trough
• any identical points
• In metres
Peak of waves correspond to areas of_______ pressure (_______), and troughs correspond to areas of ______ pressure (_______) that’s why there are peaks and troughs on waves.
• Compression =
• Rarefaction =
Peak of waves correspond to areas of high pressure (compression), that’s why there are peaks and
troughs on waves.
• Compression = peak
• Rarefaction = trough
Difference between periodic and aperiodic wave
Periodic wave: predictable, repeats itself. DIAGRAM
Aperiodic: Any sound that doesn’t repeat a basic pattern
Difference between complex sound and pure tones
Complex sound: Sounds made up of two or more frequencies. The tone of the lowest
frequency is the “fundamental frequency”, the others are “overtones”. The overtones may
be whole number multiples of the fundamental frequency - in which case are called
harmonics.
• Pure tone: An audible tone that can be represented by a sine wave; Pure tones are only
of one frequency of vibratio
What is a cycle and how is it measured? Include units
One complete vibration (rotation), made up of one area of compression (high pressure) and one area of rarefaction (low pressure).
Cycle = 1 compression + 1 rarefaction → Metres
To measure it is the line (distance from start of peak and end of trough) – in metres.
What’s a period
Time it takes one cycle to occur
What is frequency and how is it measured ? Include units
How many cycles occur per second.
Measured in Hertz
• Longer wavelength = _______ frequency sound= __________ vibrations
• shorter wavelengths= _______higher frequency sound = ______ vibrations
• Longer wavelength = low frequency sound= fewer vibrations
• shorter wavelengths= higher frequency sound = more vibrations
What is the frequency of a 6 cycle per second sound? Include units
6 Hz (hertz) per second
Why can’t we measure pitch?
We can’t measure pitch as its subjective, it is the subjective sensation of frequecncy
What is the human auditory field/dynamic range?
frequencies between 20Hz - 20,000Hz (20kHz)
What frequencies are Infrasounds and Ultra sounds? Give examples of the animals that come in these ranges
Infrasound = Sounds below 20Hz (elephant, mole)
Ultrasound = all sounds above 20kHz (bat, dolphin)
When older, hearing begins to decline from ______ frequencies
Higher
What is amplitude and how is it measured? Include units
Amplitude is the distance from normal pressure to the point of maximum displacement
(equal to the height of the wave).
Measured in Decibels sound pressure level (dBSPL)
Further it deviates from normal atmospheric pressure, it is louder
Why are peaks higher for louder sounds?
Increased force, particles move further creating larger compressions and rarefactions.
Further it deviates from normal atmospheric pressure, it is louder
Is loudness objective or subjective?
Loudness is the subjective sensation of amplitude and cannot be measured
Height of wave =
Length of wave =
Height of wave = amplitude/loudness
Length of wave = frequency/pitch
What is sound diffraction, and what frequencies/wavelengths diffract best?
Diffraction – how sound bends.
• Shorter wavelengths/high pitch don’t travel or bend that well
• Longer wavelength / low pitch – diffract better bc can withstand movements
Describe sound resonance?
Resonance is a phenomenon that occurs when an object or system is subjected to an external force or vibration that matches its natural resonant frequency (Natural resonant frequency is the objects frequency at which it vibrates the most )
When this happens, the object or system absorbs energy from the external force and starts vibrating with a larger amplitude.
Sound equations
Distance and time
Frequency and wavelength
D top then V T
V top then F W
