COMD 5070 Exam 3 Complete Solutions
the nature of science - the scientific method
1. empirical - based on data
2. deterministic - obeys physical laws
3. predictive - if you do this, then that will happen
4. parsimonious - uses the simplest explanation possible
scientific approach involv...
COMD 5070 Exam 3 Complete Solutions
the nature of science
- the scientific method
1. empirical
- based on data
2. deterministic
- obeys physical laws
3. predictive
- if you do this, then that will happen
4. parsimonious
- uses the simplest explanation possible
scientific approach involves collecting data so that we can understand the given phenomenon from our
own direct experience
transverse waves
- pebble in a pond
- ripples spread outward
- wave travels across the surface
- objects bob up and down only
- they dont move horizontally with the wave
- the wave in a stadium is a transverse wave
longitudinal waves
- pull a slinky until moderately stretched
- equal tension all along the spring
- pulse one hand inward & back again
- local change in tension
- shockwave travels along the slinky
in silence
- air molecules are equally spaced (slinky)
- pressure rises (compression)
- pressure drops (rarefractions)
- compressions/rarefractions alternate rapidly
,sound transmission through air
- vibrations will travel through air as the molecules move back & forth-air molecules moves right left &
right multiple times in a vibrating pattern
- the molecule next to the item that made the sound is not the one going all the way into the ear.
- molecules push/pull their neighboring air molecules
- the vibration then travels, (because its carried on through the molecules) not the molecules
themselves as they return back to their original home and vibrate around their home position
- sound cannot travel through the vacuum of space
frequency to period
1/ frequency (Hz) = period
- amount of time it takes for 1 full oscillation to occur( going from displacement - away from resting
position - beyond resting position- to negative side - & back to rest)
- opposite of frequency
- looks at 1 cycle
period to frequency
1/periods in seconds = frequency
- how often the air molecules vibrate
- how often the molecules leave & return back home
- measured in Hz (Hertz)- 1 Hz means 1 osscilation or 1 vibration per second- higher frequency, higher
pitch
- frequency = over time
harmonic series
- combined multiple waves/pure tones- integer whole number multiples of the fundamental
frequency(additional components above the fundamental)
- tones have a mathematical relationship that will be combining
ex: if the fundamental frequency is 100Hz, the harmonics is 200, 300, 400, 500,
- results in a periodic wave form
- repeats perfectly predictably
transmission of sound when medium changes
-Sound will travel the most readily through a medium that is continuous ,that does not change in its
properties from one place to another
- air is a medium
- air molecules oscillate with sound
- energy transmits through similar mediums
, - change of medium will change if sound is -> reflection (reflected) vs transmission (transmistted)
- talking to a submerged swimmer -> medium changed & now you have to speak up, more sound is
being reflected than transmitted
- reflection can happen where tube size changes
adding decibels
how many dB increases for 2 identical sounds?
- 6dB increase for 2 identical sounds
1. add pressure
2. compute the dB
ex: 100,000pascal came out to 74dB-because it was 2 cars it would be 200,000 (added the pressures
together)
-the reference number is 20 so, 200,00/20 = 10,000
-then do the log 20x lot (10,000) = 74dB
- because the dB were the same in the beginning it would be 74 + 74 so we dd 6dB so the answer is 80dB
- using raw uPa would be awkward, thats why we convert to dB
double sound pressure add 6dB*
ex: If you add a 50 dB sound to a 50 dB sound, the combined intensity would be = 56dB
octaves
the doubling (up) or halving (down) of the frequency
- ex: going from 400Hz to 800Hz would be 1 octave
- you can go up and down octaves- every time you change the octave the mathematical relationship
between the frequency changes
- some notes pair blends harmoniously
- some note pairs are dissonant
- harmonic frequencies match or don't- has 12 semitones
ex: If there are 12 semitones between 100 Hz and 200 Hz, how many semitones would there be
between 500 Hz and 4000 Hz. Hint: first determine how many octaves, then multiply to get semitones.=
36
semitones
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