Exp SPA - Chp 12 General Wave Properties

a) describe what is meant by wave motion as illustrated
by vibrations in ropes and springs and by waves in a
ripple tank
b) show understanding that waves transfer energy without
transferring matter
c) compare transverse and longitudinal waves and give
suitable examples of each
LEARNING OBJECTIVES

 How does a Kallang Wave look like?
 The Kallang wave moves around the stadium, but the
people do not.
 How do people move in a Kallang Wave?
KALLANG WAVE

 A wave is a disturbance that transfers energy from
one place to another.
 It is made up of periodic motions – motion repeated
at regular intervals.
 We can also call it periodic oscillations. (recall
pendulum)
INTRODUCING WAVES

1. Kinetic energy from the moving hand
is transferred to the rope.
2. This forms a rope wave (a wave that
travels within the rope).
3. The rope wave moves from the hand
to the wall (left to right).
4. As the wave moves through the rope,
from left to right, the rope particles
(P and Q) move up and down, about
their rest positions.
5. Eventually, the kinetic energy is
transferred from the hand to the
wall.
INTRODUCING WAVES
WAVES IN A ROPE

 Kinetic energy from the dipper is
transferred to the water.
 This forms a water wave (i.e. a water
ripple).
 The water wave moves outwards from
the dipper.
 The water particles move up and
down, about their rest positions.
 In other words, the kinetic energy
gets transferred from the dipper to
the edges of the ripple tank.
INTRODUCING WAVES
WAVES IN A RIPPLE TANK

 The source of a wave is a vibration or an oscillation.
 Waves transfer energy from one point to another.
 Waves transfer energy without transferring the
medium (i.e. rope or water).
In another words, the particles do not move forward
with the wave.
INTRODUCING WAVES
SUMMARY

 Observe how I move the spring. Describe the motion
of the spring.
 If we move the spring in an up-down motion:
 The spring coils move perpendicular to the direction
of the wave.
INTRODUCING WAVES
WAVES IN A SPRING
(top view)
up
down
Wave direction

 If we move the spring in a push-and-pull motion:
 The spring coils move parallel to the direction of the
wave.
INTRODUCING WAVES
WAVES IN A SPRING
Wave direction

 From the Slinky Spring, we can see that there are 2
types of waves.
Transverse waves
Longitudinal waves
INTRODUCING WAVES
TYPES OF WAVE MOTION
How do transverse waves differ
from longitudinal waves?

 The coils move up and down,
while the wave moves from left
to right.
 The movement of the coils is
perpendicular to the wave
motion.
 E.g. Electromagnetic waves i.e.
light, infrared-red, ultraviolet
INTRODUCING WAVES
TRANSVERSE WAVES
Transverse waves are waves
that travel perpendicular to the
direction of the medium’s
particle vibration.

 The coils move left and right,
while the wave moves from left
to right.
 The movement of the coils is
parallel to the wave motion.
 Examples: Sound waves
INTRODUCING WAVES
LONGITUDINAL WAVES
Longitudinal waves are waves
that travel parallel to the
direction of the medium’s
particle vibration.

 In longitudinal waves, the part where the particles of
matter are close together is called the compression.
 The part where the particles are spread apart is
called the rarefaction.
 Longitudinal waves are formed by a series of
compression and rarefactions.
INTRODUCING WAVES
LONGITUDINAL WAVES

 Describe and explain the motion of the Styrofoam
balls (if any) when the rod is dipped quickly into the
water and then removed.
INTRODUCING WAVES
rod
water
Styrofoam balls

 Is the wave formed transverse or longitudinal?
INTRODUCING WAVES
rod
water
Styrofoam balls

 What is a wave?
 2 kinds of waves
 Transverse – particles move perpendicular to wave motion
 Longitudinal – particles move parallel to wave motion
SUMMARY

a) define speed, frequency, wavelength, period and
amplitude
b) state what is meant by the term wavefront
c) Recall and apply the relationship velocity = frequency ×
wavelength to new situations or to solve related
problems
LEARNING OBJECTIVES

 When describing a wave, there are a lot of scientific
terms.
 Therefore we want to understand what does each
term means.
PROPERTIES OF WAVE MOTION

 When water waves are produced,
the peaks of the waves forms a
circle and move outwards from
the sources of disturbance.
Definition
 Wavefront is the line that joins
all the peaks of a wave or all
identical points on a wave.
DESCRIBING WAVES

 Plane waves can be produced by disturbing the water
surface with a vibrating wooden bar.
 The wavefronts of plane wave are straight lines that
moves away from the source of disturbance.
DESCRIBING WAVES

 Crests – the highest point of a transverse wave
 Troughs – the lowest point of a transverse wave
 Which of the points labelled on the wave are crests
and which are troughs??
DESCRIBING WAVES
P
Q
R
S
T
U
V

DESCRIBING WAVES
The amplitude A of a wave is the maximum possible
displacement of a point from its rest position.
P
Q
R
S
T
U
V
amplitude
(height of crest)
amplitude
(depth of trough)

DESCRIBING WAVES
Points along a wave are in phase if they have the same
• direction;
• speed;
• displacement from their rest positions.
P
Q
R
S
T
U
VQuestion
Which points on the
wave are in phase?
1. P, S, V
2. Q, T
3. R, U

DESCRIBING WAVES
The wavelength l of a wave is the shortest distance
between any two points in phase.
P
Q
R
S
T
U
Vwavelength
wavelength
wavelength

DESCRIBING WAVES
The frequency, f, is the number of complete waves
produced per second.
 SI Unit of frequency is the hertz (Hz).
 SI Unit of period is the seconds (s).
𝑻 =
𝟏
𝒇
The period, T, is the time taken to produce one complete
wave.

DESCRIBING WAVES
 Looking at the ripple tank.
Frequency Period
5 waves produced in 1 second.
𝐅𝐫𝐞𝐪𝐮𝐞𝐧𝐜𝐲, 𝒇 = 𝟓 𝑯𝒛 𝐏𝐞𝐫𝐢𝐨𝐝, 𝐓 =
𝟏
𝒇
=
𝟏
𝟓
= 𝟎. 𝟐 𝐬

DESCRIBING WAVES
 In one period, what is the distance moved by a wave crest?
 The wave moves by 1 wavelength.
 𝐒𝐩𝐞𝐞𝐝 𝐨𝐟 𝐰𝐚𝐯𝐞 =
𝐝𝐢𝐬𝐭𝐚𝐧𝐜𝐞 𝐭𝐫𝐚𝐯𝐞𝐥𝐥𝐞𝐝 𝐛𝐲 𝟏 𝐰𝐚𝐯𝐞 𝐜𝐫𝐞𝐬𝐭
𝐓𝐢𝐦𝐞 𝐓𝐚𝐤𝐞𝐧
=
𝐰𝐚𝐯𝐞𝐥𝐞𝐧𝐠𝐭𝐡
𝐩𝐞𝐫𝐢𝐨𝐝
𝑣 =
l
𝑇
= l ×
1
𝑇
= l × 𝑓 = 𝑓l
 Therefore 𝒗 = 𝒇l is the formula for speed of waves.
Wave speed v is the distance travelled by a wave per
second.

DISPLACEMENT-DISTANCE GRAPH
 A picture capture of the wave motion at a specific time, for
e.g. at t = 0 s.
 From the displacement-distance graph, we can find the
amplitude, A and wavelength, l of the wave.
P
Q
R
S
T
U
V

DISPLACEMENT-TIME GRAPH
 Follow 1 particle on the wave, say ribbon Q.
 We then used the information to plot the
displacement of ribbon Q over a period of
time.
P
Q
R
S
T
U
V

DISPLACEMENT-TIME GRAPH
 From this graph, we can find the amplitude, A and period, T of
the wave.

 Wave Terms:
 Wavefront
 Amplitude
 Wavelength
 Frequency
 Period
 Wave speed
 Wave graphs
 Displacement-distance graph
 Displacement-time graph
SUMMARY

A wave in a string is travelling to the right at 2 m s–1.
The diagram below shows its displacement–distance graph at
t = 0 s.
a) Sketch the graph to show how the wave will appear at
t = 3 s.
b) Draw and label the position of P and Q at t = 3 s.
PRACTICE QUESTION 1
Displacement/m
Distance/m
P
82 4 6
Q

Solution
PRACTICE QUESTION 1
x/m
d/m
P
t = 3 s
x/m
d/m
P
82 4 6
Q
Q
t = 0 s

A wave in a string is travelling to the right at 2 m s–1.
The diagram below shows its displacement–distance graph at
t = 0 s.
Plot a graph to show how the displacements of particles P and
Q vary with time.
PRACTICE QUESTION 2
Displacement/m
Distance/m
P
82 4 6
Q

Solution
PRACTICE QUESTION 2
Displacement/m
P
Time/sQ
421 3

Exp SPA - Chp 12 General Wave Properties

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