Waves Introduction
• What Waves Are
• Types of Waves
• Transverse vs.
Longitudinal Waves
• Frequency, Hertz, Period
• Amplitude
• Crests, Troughs, and
Wavelength
• Universal Wave Equation
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Waves
• Waves are disturbances which transfer energy
over a distance
• They all originate from vibrations
• i.e. dropping a pebble into water
• Examples:
• Water waves
• Waves in a string
• Earthquake waves
Waves
• The vibrating source supplies
energy which is transported along
the medium as a wave
• This vibration can be caused by
many things from moving a string,
rubbing objects together or having
an object impact the ground or
water
• i.e. seismic waves are waves of
energy created by earthquakes
which travel through the earth and
are caused by tectonic plates
moving against each other
Waves
• Waves pass their energy from one particle to
another until it runs out of energy
• Example: Water waves created from tectonic
activity, volcanic eruptions, winds, impacts, etc.
carry a lot of energy which can be used to inflict
serious damage
1
2
Waves
We will be discussing two main types
of waves
1) Transverse Waves
2) Longitudinal Waves
Transverse Waves
The particles vibrate perpendicular to the
direction of motion
Longitudinal Waves
The source vibrates parallel to the
direction of motion
Transverse vs.
Longitudinal Waves
3
Terminology
Regarding any kind of vibrating object:
• One complete oscillation is called a cycle
• The number of cycles per second is the frequency (f)
• The unit for frequency is the hertz (Hz)
• The time required for one full cycle is the period (T)
• The unit is usually the second but can be days,
months, years, etc.
One complete cycle
Frequency and Period
They are reciprocals of each other
therefore,
1
𝑓=
𝑇
1
𝑇=
𝑓
Amplitude
The distance from rest position to
maximum displacement is the amplitude
Amplitude
Check Your Understanding
A mass hung from a spring vibrates 15 times in 12 s.
Calculate
a) the frequency.
b) the period of the vibration.
Check Your Understanding
A mass hung from a spring vibrates 15 times in 12 s.
Calculate
a) the frequency.
b) the period of the vibration.
Answer: a) f = 1.3 Hz
b) T = 0.80 s
Check Your Understanding
The amplitude of a child swinging on a swing is 1.2 m.
What total distance does she travel after 3 complete
cycles?
Check Your Understanding
The amplitude of a child swinging on a swing is 1.2 m.
What total distance does she travel after 3 complete
cycles?
Answer: 14.4 m
A Few More Terms
• Crests - High section of
the wave
• Troughs - Low section of
the wave
• Wavelength (in m) Distance from crest to
crest or from trough to
trough
Universal Wave Equation
• Recall:
• Regarding waves, the distance travelled is the
wavelength (𝜆 in m) and the time is the period (T)
which is the time to complete a wavelength in s
therefore,
• The wave equation works for all waves, visible and
invisible
Check Your Understanding
The wavelength of a water wave in a ripple tank is 0.080 m.
If the frequency of the wave is 2.5 Hz, what is its speed?
Check Your Understanding
The wavelength of a water wave in a ripple tank is 0.080 m.
If the frequency of the wave is 2.5 Hz, what is its speed?
Answer: 0.20 m/s
Check Your Understanding
The distance between successive crests in a series of
water waves is 4.0 m and the crests travel 9.0 m in 4.5 s.
What is the frequency of the waves?
Check Your Understanding
The distance between successive crests in a series of water
waves is 4.0 m and the crests travel 9.0 m in 4.5 s. What is
the frequency of the waves?
Answer: 0.50 Hz
Check Your Understanding
The period of a sound wave from a piano is 1.18 × 10–3
s. If the speed of the wave in the air is 3.4 × 102 m/s,
what is its wavelength?
Check Your Understanding
The period of a sound wave from a piano is 1.18 × 10–3 s. If
the speed of the wave in the air is 3.4 × 102 m/s, what is its
wavelength?
Answer: 0.40 m