3. What is a wave?
a pattern of disturbances (oscillations,
vibrations) caused by the movement of
energy through matter or space
4. What is a wave?
a pattern of disturbances (oscillations,
vibrations) caused by the movement of
energy through matter or space
5. What is a wave?
a pattern of disturbances (oscillations,
vibrations) caused by the movement of
energy through matter or space
6. Waves can be classified according to their nature.
Mechanical waves
Electromagnetic waves
7. Waves can be classified according to their nature.
Mechanical waves
Electromagnetic waves
require a medium (matter) to travel through
Sound waves, water waves, ripples in strings
or springs are all examples of mechanical
waves.
8. Waves can be classified according to their nature.
Mechanical waves
Electromagnetic waves
require a medium (matter) to travel through
Sound waves, water waves, ripples in strings
or springs are all examples of mechanical
waves.
do not require a medium (matter) to travel
through – they can travel through space
Radio waves, visible light, x rays
9. Waves can be classified by direction of vibration
Tranverse waves
Longitudinal waves
10. A wave where the medium particles vibrate at
right angles to the direction of energy
transfer is called a transverse wave.
Look carefully at the motion of ONE of the
particles in this transverse wave!
11. Waves can be classified by direction of vibration
Tranverse waves
Longitudinal waves
direction of energy transfer
direction of vibration
12. Sound is an example of longitudinal wave
Look carefully at the motion of ONE of the
particles in this longitudinal wave!
A tuning fork causes
surrounding air molecules
to vibrate back and forth.
Direction of sound travel
13. Waves can be classified by direction of vibration
Transverse waves
Longitudinal waves
direction of energy transfer
direction of vibration
direction of
vibration
direction of
energy transfer
14. Wave pulses travel through a medium and
therefore transfer energy.
Particles in the medium are moved back and
forth by each pulse but are not transferred
from one place to another.
direction of energy transfer
Vibration of metal atoms in the
spring (the medium)
BIG IDEA!
WAVES TRANSFER ENERGY NOT MATTER!
21. Increasing the rate of water droplets falling
creates more disturbances per unit time.
This is called the
frequency.
Each disturbance has less time to travel
before the next is created – so ripples are
closer together
23. What happens when
the frequency of the
source (drops) is
increased?
More drops per
second, more waves
per second, waves
are closer together.
24. What happens when
the amplitude of the
source (drops) is
increased?
This would be caused
by the drops hitting
the water with more
force.
25. Increasing the height or size of the falling
water droplet is a BIGGER disturbance.
The height of the ripples increases. This is
called the amplitude of the wave.
26. What happens when
the amplitude of the
source (drops) is
increased?
This would be caused
by the drops hitting
the water with more
force. How?
27. A cork placed in the dish will bob up and
down as the waves passed by.
The relative position of the cork does not
change.
28. You can think of the cork as representing a
molecule of water (the medium)
So, the relative position of water molecules
does not change (only motion is up and
down)
30. Describing Waves
Waves are created by vibrating objects
ONE vibration = ONE cycle = ONE oscillation
(all describe one complete back and forth motion)
FREQUENCY: the number of vibrations each
second. Measured in s-1 (or Hertz). The symbol
for frequency is f.
A frequency of 12 Hz means that there are 12
complete waves generated each second!
PERIOD: the time required for one vibration.
Measured in seconds. The symbol for period is T.
31. WAVELENGTH: How far the wave energy travels
in one complete vibration.
This is the distance traveled in an amount of
time equal to the period of the wave.
The symbol for wavelength is the Greek letter
lambda (l).
32. Wavelength is measured as the distance
between identical points on two successive
waves.
33. AMPLITUDE: a measure of the maximum
distance the particles in the medium are
displaced from their resting position as the
wave passes.
It is easier to visualize these characteristics by
looking at plots
Direction of Energy transfer
transverse
vibration
longitudinal
vibration
34. AMPLITUDE: a measure of the maximum
distance the particles in the medium are
displaced from their resting position as the
wave passes.
It is easier to visualize these characteristics by
looking at plots
Direction of Energy transfer
transverse
vibration
longitudinal
vibration
35.
36. Activity 2 – Examining Wave Motion in a
Slinky Spring
37. A continuous wave is produced when a
series of pulses are generated by a
vibrating source.
One shake produces a
single vibration (a
wave pulse). If the
end of the spring is
shaken back and forth,
a continuous series of
pulses is produced.
This is a standing wave
pattern.
38. Longitudinal pulses can be produced by
holding spring coils together at one end and
then releasing.
A continuous wave can be produced by
sliding the end of the spring back and forth
towards your partner (holding the fixed end)
39. Longitudinal pulses can be produced by
holding spring coils together at one end and
then releasing.
A continuous wave can be produced by
sliding the end of the spring back and forth
towards your partner (holding the fixed end)
43. Displacement – Position Graphs
A displacement – position plot shows the
different position of a particles in the medium
at a given time for a section of the wave.
Consider a rope that is being vibrated at one
end. If we took a snapshot with a camera it
might look like this.
46. Longitudinal waves are a bit tricky to understand
because the direction of vibration is not
perpendicular to the direction of wave travel.
Consider the following images
compression
rarefaction
l
47. -1.5
-1
-0.5
0
0.5
1
1.5
position
displacement
In longitudinal waves, the maximum and
minimum displacements are called
compressions and rarefactions respectively.
The distance between centers of two
successive compressions OR rarefactions
would be the wavelength
center of
compression
center of
rarefaction
l
48. -1.5
-1
-0.5
0
0.5
1
1.5
Displacement-Time Graphs
A displacement – time plot shows how the
position of a particle in the medium changes
as it vibrates back and forth.
Transverse and longitudinal waves look the
same on this type of plot. The only difference
is the direction of the particle displacement.
time
displacement
49. -1.5
-1
-0.5
0
0.5
1
1.5
Amplitude can be measured on the y-axis.
time
displacement
Period can be measured on the x-axis.
The period would be the time for one complete wave.
50. Wave Speed
The speed of a wave is determined by the
properties of the medium it travels through.
Properties include:
51. Wave Speed
The speed of a wave is determined by the
properties of the medium it travels through.
Properties include:
• type of material
• elasticity
• tension
• density (solid, liquid or gas)
• temperature
distance
speed=
tim e
Speed is calculated using the following
equation.
53. Recall:
The definition of period
The definition of wavelength
the time it takes to complete one
vibration/oscillation/cycle
the distance a wave travels in a complete
vibration/oscillation/cycle
57. Practice:
1. Find the speed of a wave in a metal spring if
a pulse travels 7.5 m in 3.0 s.
2. What is the frequency of this wave if the
distance between two successive wave
crests is 0.25 m?
3. Challenge: A fisherman passes the time by
counting waves passing under his boat. He
notices that his boat rises and falls 8 times
in 65 seconds. He counts 6 wave crests
between his boat and a buoy located 54 m
away. What is the speed of the water
waves?
