Properties of
Waves and Wave
Interactions
Mark Lesmeister
Pearland ISD Physics
Some physics graphics © Copyright 2002 Holt Rinehart and Winston
PART 1: INTRODUCTION TO
WAVES
Definition of Waves

A wave is the motion of a disturbance of some
physical quantity.

A wave transfers energy without a large-scale
transfer of matter.
Waveform diagram

A wave can be represented with a
waveform diagram.

A waveform diagram shows the position of each
point of the medium at a moment in time, or the
position of a single point over time.
PART 2: TYPES OF WAVES
Mechanical & Nonmechanical
Waves


Mechanical waves
require a material
medium.
Examples are:
 Sound
waves
 Water waves
 Shock waves in an
explosion


Other waves, such as
electromagnetic
waves, do not require
a material medium.
Examples are:
 Light
 X-rays
 Radio
waves
Pulse Waves and Periodic Waves

Pulse wave- a wave which consists of a
single, non-repeated disturbance or pulse.
Animation courtesy of Dr. Dan Russell,
Kettering University
Pulse Waves and Periodic Waves

Periodic wave- a wave whose source is
some form of periodic motion.
Animation courtesy of Dr. Dan Russell,
Kettering University
Sinusoidal Waves

A periodic wave whose source vibrates
with simple harmonic motion produces a
sinusoidal wave.
 This
is a wave whose graph is shaped like a
sine or cosine graph.
Quick-lab 1: Types of Waves

Using the thin coiled spring, send a single pulse
down the spring as demonstrated by your
instructor.



In which direction was the wave energy moving?
In which direction(s) did the spring move?
Using the slinky spring, send a single pulse
down the spring, as demonstrated by your
instructor.


In which direction was the wave energy moving?
In which direction did the spring move?
Transverse and Longitudinal
Waves

Transverse wave – a wave whose particles vibrate
perpendicular to the direction of travel of the wave.
Animation courtesy of Dr.
Dan Russell, Kettering
University

Examples include:


Surface waves on water.
Electromagnetic waves
Transverse and Longitudinal
Waves

Longitudinal wave- a wave whose particles vibrate
parallel to the direction of travel of the wave.
Animation courtesy of Dr.
Dan Russell, Kettering
University

Examples include:


Sound waves
Compression waves in explosions.
Transverse Wave

A transverse wave has crests and troughs.
© Copyright 2002 Holt Rinehart and Winston
Longitudinal Waves


Longitudinal waves are sometimes referred to as
density waves.
They can be represented by the same
waveforms as transverse waves.
© Copyright 2002 Holt Rinehart and Winston
PART 2: CHARACTERISTICS
OF WAVES
Frequency and Period

Frequency – the number of crests (or troughs) passing a
reference point per second.



Period – the time between the passage of two
successive wave crests (or troughs) past a reference
point.


Frequency is measure in cycles/second
1 Cycle/second = 1 s-1 = 1 Hertz
The period is a time interval, so it is measured in seconds.
The frequency is the reciprocal of the period.

We also say frequency and period are inversely related.
Wavelength

wavelength () – distance between two
adjacent similar points of the wave, such
as from crest to crest or trough to trough
 It
is also the distance advanced by the wave
motion in one period.
© Copyright 2002 Holt Rinehart and Winston
Quick Lab 2: Wave Speed

Using the coiled spring to send transverse
pulse waves. Using the stopwatch, time
how long it takes for the pulse to travel the
length of the spring. Try timing the speed
of pulses with different amplitudes.
Wave Speed



Wave speed: The speed of the moving
disturbance.
distance travelled 
v

time interval
T
v=f
Quick Lab 3: Wave Equation

Using the coiled spring to make transverse
waves. Change the frequency of the
waves and observe what happens to the
wavelength.
Wave Speed Practice Problem
A tuning fork produces a sound with a
frequency of 256 Hz and a wavelength in
air of 1.35 meters.
 What is the speed of sound in air?
 Answer: v = 346 m/s

Amplitude

amplitude – the maximum displacement of
the vibrating particles of the medium from
their equilibrium positions.
 The
amplitude of a wave is related to the
energy transported by the wave.
© Copyright 2002 Holt Rinehart and Winston
Power and damping

power- the rate of transfer of energy by a
wave.
 The
power of a wave is proportional to the
square of the wave amplitude and also to the
square of the wave frequency

damping – the reduction in amplitude of a
wave due to the dissipation of wave
energy as it travels away from the source.
PART 4: INTERACTIONS OF
WAVES
Quick Lab 4: Wave Interactions
Using the Slinky ® or the thin coil spring,
have students on both end of the spring
launch pulses as the same time.
 Experiment with what happens when two
pulses meet in the middle of the spring.

Superposition

superposition – the combination of two
overlapping waves.
 When
waves overlap, the displacements of
the waves at each point are added to find the
resultant displacement.
Animation courtesy of Dr. Dan Russell,
Kettering University
Constructive Interference
constructive interference – when individual
displacements on the same side of the
equilibrium position are added together to
form the resultant wave.
 The resultant displacement is larger than
either of the component displacements.

Constructive Interference
© Copyright 2002 Holt Rinehart and Winston
Destructive Interference
destructive interference – when individual
displacements on opposite sides of the
equilibrium position are added together to
form the resultant wave.
 The resultant is smaller than at least one
of the component displacements.

Destructive Interference
© Copyright 2002 Holt Rinehart and Winston
Interference Patterns

Waves that meet form interference
patterns.
Wave Reflection

reflection- the turning-back of a wave
when it strikes a boundary.
Wave Reflection at a Fixed
Boundary

At a fixed boundary, waves are reflected
and inverted.
Animation courtesy of Dr. Dan Russell,
Kettering University
Wave Reflection at a Free
Boundary

At a free boundary, waves are reflected
upright.
Animation courtesy of Dr. Dan Russell,
Kettering University
Wave Reflection
© Copyright 2002 Holt Rinehart and Winston
Quick Lab 5: Standing waves

As demonstrated by your instructor, shake
the spring with a gradually increasing
frequency, and observe what happens at
certain fast enough frequencies.
Standing Waves

standing wave – a wave pattern that
results when two waves of the same
frequency, wavelength, and amplitude
travel in opposite directions and interfere.
Animation courtesy of Dr. Dan Russell,
Kettering University
Standing Waves

node – a point in a standing wave that
always undergoes complete destructive
interference and therefore is stationary.

antinode – a point in a standing wave,
halfway between two nodes, at which the
largest amplitude occurs.
Standing Waves
© Copyright 2002 Holt Rinehart and Winston
Types of Waves:
De Broglie Waves