Psych 3A03 11 September 2013
McMaster University Paul A. Faure
Instructions and Tips
• Assume the speed of sound in air (c ) iair 340 m⋅s .
• Assume the speed of sound in water (c wateris = 4⋅cair
• A calculator is not necessary to answer any of these questions.
1. Why does atmospheric pressure decrease with elevation?
Pressure = Force/Area & Force = mass⋅acceleration. Atmospheric pressure is the force of air
molecules over the area of the Earthʼs surface. The force of gravity results in a higher
density (ρ = mass/volume) of air molecules at the Earthʼs surface than at higher elevations
and thus a higher static air pressure.
2. Contrast transverse (shear) wave motion with longitudinal wave motion?
In transverse wave motion, particle displacement is perpendicular to the direction of wave
propagation, whereas in longitudinal wave motion particle displacement is parallel to the
direction of wave motion.
3. What are the units of measure for Force, Work, Frequency, Wavelength, Period, and Pressure?
Force = Newton (1 Nt = kg⋅m⋅s ); Work = Nt⋅m (Force⋅distance); Frequency = Hz (cycles⋅s ); -1
Wavelength = meters (m); Period (Τ) = seconds (s); Pressure = Pascal (1 Pa = Nt⋅m )
4. Name three physical attributes of sound that are encoded by the peripheral auditory system.
frequency (f), amplitude (A) (or intensity), time (s)
5. Name the physical attributes of sound that are required to completely describe a sine wave.
frequency (f), amplitude (A), starting phase angle (θ)
6. A sine wave has a peak-to-peak amplitude (A peak-to-peakof 20 Volts. What is its peak (Apeak) and rms
amplitude (A rms)?
Apeak = 10 V ; Arms = 7.07 V
7. A sine wave has a rms amplitude (A rms) of 10 Volts. What is its peak amplitude (A peak?
Arms = A peak/√2 ; Apeak = A rms⋅√2 ; A peak=14.14 V
8. An object exhibiting uniform circular motion has an angular velocity of 628.318 radians ⋅s . What is its
frequency of oscillation?
ω = 2π⋅f ; f = ω/2π; ω = 628 radians⋅s ; -1 f = 100 cycles⋅s or Hz
9. A frequency of 4 Hz corresponds to what angular veloc