1. Chapter 9: Introduction to Waves
Section 1: The Nature of Waves
Section 2: Wave Properties
The Behavior of Waves

2. Section 1: The Nature of Waves
What is a wave?
Wave – a repeating disturbance or movement that transfers energy through matter or space
Waves carry energy without transporting matter from place to place
A wave will travel only as long as it has energy to carry
Mechanical waves – waves that can only travel through matter
Medium – the matter through which a mechanical wave can travel
The medium can be either a solid, liquid, or gas
Two types of mechanical waves:
Transverse wave – the matter in the medium moves at right angles to the direction the wave is traveling example: a wave traveling through water
Compressional wave – the matter in the medium moves parallel to the direction the wave is traveling example: a sound wave

3. Section 2: Wave Properties
Describing Waves
Amplitude
Crests
Troughs
Wavelength
rest position
Characteristics of a Transverse Wave
Compressions
Rarefactions
Wavelength
Characteristics of a Compressional Wave

4. Section 2: Wave Properties
Properties of Waves
Wavelength () – distance between one point on one wave and the nearest point just like it on the following wave
Units: distance units, usually meter
Frequency (f) – how many wave lengths pas a fixed point each second
Units: either /second (waves or cycles/second) or hertzs (Hz)
Note: frequency is always reported in hertz (Hz), during math computations that unit is converted to /s (per second)
Relationship between wavelength and frequency: as frequency increases, wavelength decreases
Period (T) – time required for one wave to pass a fixed point
Unit: second
Relationship between period and frequency: the frequency of a wave is the inverse of the wave’s period, and vice-versa:

5. Section 2: Wave Properties
Wave speed (v) – the product of wavelength and frequency
Wave speed = wavelength x frequency, or:
Example: a wave has a length of 0.25-m, and a frequency of 50-Hz. What is its speed?
Solution
Amplitude – a measure of the energy in a wave
The greater the amplitude, the greater the energy
In a compressional wave the amplitude is related to how tightly the particles in the medium are pushed together at the compressions and how far apart they in rarefaction
In a transverse wave the farther the wave travels from the rest position the greater the amplitude
λ = 0.25m
f= 50.0 Hz = 50/s
v= ?
𝑣=𝜆𝑓
𝑣=0.25𝑚 50 𝑠
𝒗=𝟏𝟐.𝟓 𝒎 𝒔

6. The Behavior of Waves
Reflection – the bouncing back of a wave when it strikes a surface or boundary
Reflection occurs when a wave strikes an object
All waves can be reflected
The Law of Reflection: The angle of the reflected wave is equal to the angle of the incident wave:
Refraction – the bending of a wave when it travels from one medium to another
The speed of the wave depends upon the medium through which it is traveling
When a wave passes from one medium to another it changes speed
The straw appears to bend because light waves travel faster in air than it does in water
Reflecting
Surface
Normal
Line
Incident
Wave
Reflected i r
Law of Reflection: =

7. The Behavior of Waves
Diffraction – the change in the direction of a wave when an object causes the wave to bend around it
Difference between diffraction and refraction: refraction occurs when waves pass through an object while diffraction occurs when waves pass around an object.
Interference – the interaction between two or more waves that occupy the same space at the same time. There are two types:

8. The Behavior of Waves Constructive – the waves add together
The amplitude of the new wave is equal to the sum of the amplitudes of the interfering waves
Destructive – the waves subtract from each other as they overlap
Occurs crest of one wave overlaps the trough of the second wave
Standing wave – a wave pattern that forms when wave equal in wavelength and amplitude, but traveling in opposite directions, constructively interfere
Nodes – points on a standing where the two waves cancel and no movement occurs
Antinodes – points on a standing wave where movement is at a maximum
Resonance – the ability of an object to vibrate by absorbing energy at its natural frequency
In the case of sound waves, the sound gets louder
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