17.2 properties of mechanical waves 17.2 key concepts what determines the frequency of a wave? how...
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17.2 Properties of Mechanical Waves
17.2 Key Concepts
• What determines the frequency
of a wave?
• How are frequency, wavelength,
and speed related?
• How is the amplitude of a wave
related to the wave’s energy?
17.2 Properties of Mechanical Waves
Frequency and Period
How do surfers know when the next wave is coming?
• If they count the ________ between two successive
crests, the next crest usually will come after this same
_________________
Any motion that repeats at a regular
time intervals is called _____________
_________________
The time required for one cycle is called the ___________
time
interval
periodic
motion
period
17.2 Properties of Mechanical Waves
Frequency and Period
Any periodic motion has a _________________, which is the number of wave cycles that pass a point in a given time.
Frequency is measured in __________________________ or ___________ (Hz).
Hz = 1/s
A wave’s frequency equals the frequency of the vibrating _________________ producing the wave.
frequency
cycles per secondhertz
source
17.2 Properties of Mechanical Waves
A. A wave vibrating at one cycle per second has a frequency of ______.
B. A wave vibrating at two cycles per second has a frequency of _______
Frequency and PeriodFrequency = 1.0 hertzOne cycle per second
Frequency = 2.0 hertzTwo cycles per second
1.0 Hz
2.0 Hz
17.2 Properties of Mechanical Waves
Wavelength
Wavelength is the ______________ between a point on one wave and the same point on the _______ ____________ of the wave
______________ the frequency of a wave _____________ its wavelength.
Long wavelength Short wavelength
distancenext cycle
Increasing decreases
17.2 Properties of Mechanical Waves
Wavelength
Which wave below has a higher frequency?
Long wavelength Short wavelength
The second one (shorter wavelength)
17.2 Properties of Mechanical Waves
For a transverse wave, wavelength is measured between adjacent _____________ or between adjacent _______________
Wavelength
crests
troughs
17.2 Properties of Mechanical Waves
For a longitudinal wave, wavelength is the distance between adjacent _______________ or _________________.
Wavelength
Rarefaction
Compression
Compression
compressions
rarefactions
17.2 Properties of Mechanical Waves
Wave Speed
If you assume that waves are traveling at a constant speed, then wavelength is ____________ proportional to frequency.
inversely
17.2 Properties of Mechanical Waves
When the wavelength is in ______________, and the frequency is in __________, the units for speed are _______________.
The speed of a wave is also calculated by dividing its wavelength by its ________________
Wave Speed
Speed = Wavelength period
metersHertz (1/s)
m/s
period
17.2 Properties of Mechanical Waves
Speed of Mechanical Waves
One end of a rope is vibrated to produce a wave with a wavelength of 0.25 meter. The frequency of the wave is 3.0 hertz. What is the speed of the wave?
Wave Speed
Speed = 0.25 m x 3.0 1/s = 0.75 m/s
17.2 Properties of Mechanical Waves
1. A wave on a rope has a wavelength of 2.0 m and a frequency of 2.0 Hz. What is the speed of the wave?
Wave Speed
Speed = 2.0 m x 2.0 1/s = 4.0 m/s
17.2 Properties of Mechanical Waves
2. What is the speed of a wave in a spring if it has a wavelength of 10 cm and a period of 0.2 s?
Speed = Wavelength
period
Wave Speed
= _10 cm_
0.2 s
= 50 cm/s
17.2 Properties of Mechanical Waves
The speed of a wave can change if it enters a ______ ______________, or if variables such as _____________ and ______________ change.
Wave Speed
new medium
temperature pressure
17.2 Properties of Mechanical Waves
Amplitude
The amplitude of a wave is the _______________ _________________ of the medium from its rest position.
The more energy a wave has, the ____________ is its amplitude.
High amplitude
Low amplitude
maximumdisplacement
greater
17.2 Properties of Mechanical Waves
The amplitude of a transverse wave is the distance from the rest position to a crest or a trough.
Amplitude
17.2 Properties of Mechanical Waves
The amplitude of a longitudinal wave is the maximum displacement of a point from its ________ position.
The more energy the
wave has, the more the
medium will be
compressed or
displaced.
Amplitude
Res
t pos
ition
rest
17.2 Properties of Mechanical Waves
Assessment Questions
1. True or False: Frequency is inversely proportional to wavelength.
17.2 Properties of Mechanical Waves
Assessment Questions
2. What is the speed of an earthquake wave if it has a wavelength of 2.5 km and a frequency of 3 Hz?a. 7.5 km/sb. 5.0 km/sc. 2.5 km/sd. 1.3 km/s
17.2 Properties of Mechanical Waves
Assessment Questions
3. The maximum displacement of a wave from its rest position is the ___________________.a. period
b. frequency
c. wavelength
d. amplitude