We’re covering:
 Progressive Waves
 What is wave motion?
 Components of wave motion
 Wave equation
Let’s go!
What is Wave Motion?
Propagation of disturbances which carries energy without transferring matter.
What causes Wave Motion?
Vibrations (oscillations).
The energy from these oscillations propagates through waves.
Wave motion can be observed as:
 Progressive Waves: travel from place to place
 Stationary Waves: do not move
This chapter will deal with progressive waves.
Waves can also be classified into:
Transverse Waves  direction of vibration is perpendicular to direction of motion 
Longitudinal Waves  direction of vibration is along direction of motion 
Examples of Wave Motion:
There are 2 major groups:
 Mechanical Waves
 Electromagnetic Waves
Mechanical  Electromagnetic 
Sound  Visible light 
Water waves  Radio waves 
Strings, Springs  Ultraviolet 
Components of Wave Motion
Component  Definition  Notation  Unit 
Displacement  Relative distance from vibrating particle to its rest position  y  m 
Amplitude  Maximum displacement of a particle  A  m 
Wavelength  Distance between 2 particles vibrating in phase  λ  m 
Period  Time taken for any particle to complete one oscillation  T  s 
Frequency  Number of oscillations any particle completes in 1 second OR Number of wavelengths that pass through any fixed point in 1 second  f = 1/T  Hz 
Speed  Distance travelled by the wave in 1 second  v  ms^{1} 
Phase Difference (see below)  Difference between the position of 2 particles in their cycles  φ 

Representing Phase Difference
The red particles are at different points in their cycle at any moment in time.
The motion of each particle can be graphed against time.
2 Red Particles  Phase Difference  Graph of each particle’s motion 
1^{st} red particle & 2^{nd }red particle  There is a phase difference: The 2^{nd} ‘lags’ behind the 1^{st}.  
2^{nd} red particle & 5^{th} red particle  There is no phase difference
They are in phase 
Calculating Phase Difference:
Unit  Definition  Notation  Example 
In metres  distance between the 2 particles  x  
In seconds  time difference between identical points in the cycles of 2 particles  t OR (x/λ)T  
In cycles  Fraction of the distance between particles against a complete wavelength OR Fraction of the time difference against a complete period  x/λ OR t/T  
In radians  Angular difference when motion of each particle is mapped onto a circle
1 cycle = 2π rad  (x/λ)2π OR (t/T)2π  
In degrees  Angular difference when motion of each particle is mapped onto a circle 1 cycle = 360°  360(x/λ)° OR 360(t/T)° 
Next, we will look at the wave equation describing speed:
v = fλ
How is the wave equation derived?
Wavelength is the distance travelled by a wave in one cycle: λ
Frequency is the number of cycles per second:
f = 1/T
Speed is distance travelled per second:
v = λ/T
Therefore:
v = fλ
*Remember:
Velocity is the SAME in the SAME MEDIUM.
Two water waves might have different f & thus λ, but they will have same v.
Two sound waves in air travel at the same speed: 343 ms^{1}
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