*
*
* Wave vs particle
* Mechancal vs non-mechancal
* Longitudinal vs Transverse
* Spreading of waves
* I. Nature of a Wave
A. Definition of wave
* A disturbance which travels through a medium from one point
in space to the others.
* A medium is the matter through which a wave travels
* E.g. pond- water; sound- air; earthquake- Earth
* Mechanical waves- require a medium
* Electromagnetic waves- do not require a medium; instead
these waves consist of changing electric and magnetic fields
* E.g. light and radiowaves
*
*Energy is transferred from one place to another
in a wave motion.
* WAVES TRANSFER ENERGY!
*Motion of the medium (particles of the medium)
is usually periodically vibratory.
*Only the shape or form of wave travels, not the
medium.
*Energy may spread out as waves travel (drop
pebble, circles get larger as they spread outwards)
*
Vibrational Motion
*Vibration: in a general sense, anything that switches
back and forth, to and fro, side to side, in and out,
off and on, loud and soft, or up and down is vibrating.
A vibration is a wiggle in time.
*Wave: a wiggle in both space and time is a wave. A
wave extends from one place to another.
*Vibrations and waves: the source of all waves is
something that is vibrating. Waves are propagations of
vibrations throughout space.
*Harmonic motion occurs when a vibration repeats
and is converted (no energy input is needed to
continue the motion)
*
• A wave is an oscillation that
travels.
• A ball floating on water can
oscillate up and down in
harmonic motion.
• The surface of the water
oscillates in response and the
oscillation spreads outward
from where it started.
*
B. Properties of Periodic Motion
• Cycle: A cycle is a unit of motion that repeats.
* B.
Categories of Waves
Waves are classified into different types
according to their natures :
WAVES
Mechanical waves
Transverse waves
Electromagnetic waves
Longitudinal waves
Transverse waves
*
• According to the direction of vibration, waves are classified into :
(a) Transverse wave; ( doing ‘the wave’, string on a door knob)
(b) Longitudinal waves (sound waves, sslinky- stretch and move
directly toward the end)
ONLINE DEMO:
http://www.acoustics.salford.ac.uk/schools/teacher/lesson1/lesson1inter
active.html
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* The waveform appears in the shape of sine curve.
* A wave in which the motions of the matter particles are
perpendicular to the direction of propagation of the wave itself.
Examples
Water waves, pulse in a stretched
string,transverse wave demonstrator.
*
*A wave in which the motions of the matter particles are
in the same direction as the wave propagation.
Sound, or a spring oscillating up and down
Examples
* 2. Based on medium
a. Mechanical Waves
* A material medium is necessary for the transmission for mechanical
waves. Mechanical waves cannot travel through vacuum.
* Due to forces on particles in the “medium” that are next to each other,
the disturbance is transmitted from one layer to the next through the
medium.
* b. Non Mechanical Waves
(Electromagnetic Waves)
*Material medium is not essential for propagation.
e/m waves travel through vacuum.
*Disturbance of electric and magnetic fields travelling
through space.
*All electromagnetic waves are transverse waves.
X-rays, radio waves, micro-waves,etc.
examples
* A.
Anatomy of a Wave
A wave is usually described by the following
terms :
* Amplitude
* Wavelength ()
* Frequency (f)
* Period (T)
* Wave velocity (v)
Each term will be explained….
* The amplitude is the maximum displacement of the medium from
its equilibrium position. The amplitude of a wave refers to the distance
from the equilibrium point (or ½ the distance from highest to lowest point of
vibration)
* The wavelength () is the minimum distance between two points
which are in phase.
* The frequency (ƒ) is the number of complete oscillations made in
one second. The frequency of a wave refers to how many “waves” pass by a
point in a given amount of time (usually a second)
Unit : Hz
* The period (T) The period of a wave is the time for a to make one
complete cycle. Period, being a time, is measured in units of time
such as seconds, hours, days or years. It is the time taken for one
complete oscillation. It is related to frequency by
Unit : s
T = 1/ƒ
* Graphing harmonic motion- using paper and string
* When oscillations are small, the motion is called simple
harmonic motion (shm) and can be described by a simple sine
curve.
* See animation
* Use construction paper- string -glue
* create a transverse wave
* Label parts
* Crest‘- highest part off rest of transverse wave
* Trough-lowest part off rest of transverse wave
* Amplitude-maximum displacement off rest
* Wavelength-distance between two points –crest to crest
* Frequency- to how many “waves” pass by a point in a
given amount of time (usually a second)
the entire sheet is one second
* Period-time for a wave to make one complete cycle.
*
*
* Flip side of transverse wave model
* create a longitudinal wave – draw slinky-like model
* Label parts
* Compression-Crest- particles – highest density
* Rarefaction -Trough-particles stretched
* Amplitude-maximum displacement off rest-compression to rest
* Wavelength-distance between two points –compression to
*
*
compression
Frequency- to how many “waves” pass by a point in a given amount
of time (usually a second)
the entire sheet is one second
Period-time for a wave to make one complete cycle.
*
E. The Wave Equation
The wave velocity is the displacement traveled by the wave in one
second ……....
The wave velocity (v) is related to
frequency and wavelength by --
The Wave Equation
v = ƒ
Using the Wave Equation
Example :
A travelling wave of wavelength 0.6m moves at a speed of 3.0 m/s. What is the
period of this wave ?
 = 0.6 m,
v = 3.0 m/s
f=?
By using the wave
equation,
v = ƒ
ƒ = v/ 
f = (3.0 m/s)/(0.6 m)
ƒ = 5.0 Hz
Then the period of this wave is ???
Period T = 1/ƒ
T = 1/5.0 or 0.2 s
*
* The speed of a wave equals the frequency times the
wavelength.
Frequency (cycles/sec)
Speed (m/sec)
v=f
Wavelength (m)
*A student does an experiment with waves
in water.
*The student measures the wavelength of
a wave to be 5 centimeters.
*By using a stopwatch and observing the
oscillations of a floating ball, the student
measures a frequency of 4 Hz.
*If the student starts a wave in one part of
a tank of water, how long will it take the
wave to reach the opposite side of the
tank 2 meters away?
* Calculate the wave equation using graph paper model
activity
* Sine curve- draw 1,2,4,5,10, 20 waves – each wave has
an amplitude of 2 blocks to crest and 2 blocks to
trough.
CALCULATE:
* Frequency-period
* wavelength
* Wave speed
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