a wave

is a rhythmic disturbance that

carries/transfers energy through

matter or space

A repeating movement

Mechanical Waves

require a medium

medium: the matter through which a

wave travels examples: water, air, anything made of matter

waves transfer energy from one point to

another with little or no permanent

displacement to the particles in the medium

Molecules pass energy along to neighbor,

who then passes energy to neighbor, etc.

All waves are produced by VIBRATIONS

Two Types of Mechanical

Waves:

1. Transverse Waves

2. Longitudinal/Compressional

Waves

Transverse Waves

waves that propagate (or move)

perpendicular to the direction of travel

crest

the point on the medium that exhibits the

maximum amount of positive or upward

displacement from the rest position

trough

the point on the medium that exhibits the

maximum amount of negative or

downward displacement from the rest

position

amplitude

the maximum displacement of a particle

on the medium from its equilibrium

position

wavelength

the length of one wave is measured

from a point on one wave to the same

point on the next wave

trough to trough

crest to crest

midpoint to midpoint

Anatomy of a Transverse Wave

Label the following parts of a transverse

wave in your notes:

equilibrium

crest

trough

amplitude

wavelength

Longitudinal Waves

waves that propagate (or move) parallel

to the direction of motion

compression

a point on a medium through which a

longitudinal wave is traveling that has

the maximum density

rarefaction

a point on a medium through which a

longitudinal wave is traveling that has

the minimum density

Anatomy of a Longitudinal Wave

Label the following parts of a

longitudinal wave in your notes:

compression

rarefaction

wavelength

Describing a Wave & Wave Speed

Frequency (f): the number of vibrations

an object makes in a unit of time

(generally one second)

the unit of frequency is Hz = 1

𝑠

𝑓 =𝑣𝑖𝑏

𝑡

Period (T): the time needed to complete

one vibration (measured in seconds)

𝑇 =𝑡

𝑣𝑖𝑏

The Sears Tower sways back and forth at

a frequency of about .1 Hz.

What is the period of vibration?

Speed Review

an object’s speed is described by the

distance traveled in a specific amount of

time (generally measured in m/s)

Wave Speed

v = λ ● f

wave speed = wavelength ● frequency

Lambda

A wave with a frequency of 60.0 Hz

travels through vulcanized rubber with a

wavelength of 0.90 m.

What is the speed of this wave?

The lowest pitch that the average

human can hear has a frequency of

20.0 Hz.

If sound with this frequency travels through

air with a speed of 343 m/s, what is its

wavelength?

A ship anchored at sea is rocked by

waves that have crests 14 m apart. The

waves travel at 7.0 m/s.

How often do the wave crests

reach the ship?

Earthquakes generate shock waves that

travel through Earth’s interior to other parts

of the world. A shock wave has a very low

frequency, typically around 0.050 Hz.

If the speed of a p-wave with this frequency is

8.0 km/s, what is its wavelength?

A dolphin can typically hear sounds with

frequencies up to 150 kHz.

What is the speed of sound in water if a

wave with this frequency has a wavelength

of .01 m?

Sonar is a device that uses reflected sound

waves to measure underwater depths.

There is a sonar signal that has a

frequency of 288 Hz. If the speed of sound

in water is 1.45x103 m/s,

what is the wavelength of

the sonar signal?

Cicadas produce a buzzing sound that has a

wavelength in air of 2.69 m. If the speed of

sound in air is 343 m/s,

what is the frequency of the sound produced

by a cicada?

What is its period?

A hiker shouts toward a vertical cliff 685 m

away. The echo is heard 4 s later.

What is the speed of sound of the hiker’s voice

in air?

The wavelength of the sound is .75 m. What is

its frequency?

What is the period of the wave?

Wave Behavior

What happens when a ball is thrown

against a wall?

Predict what would happen if a wave

encounters a rigid boundary?

When a wave pulse is sent down a medium

connected to a rigid wall,

the energy transmitted

is reflected.

The reflected wave

is inverted due to

Newton’s Third Law of

Motion.

Predict what would happen if two waves were

in the same place on a medium.

Principle of Superposition

the displacement of a medium caused by two or

more waves is the algebraic sum of the

displacements of the individual waves two or more waves can combine to form a new wave

the result of the superposition of two or more

waves is called interference

Two Types of Interference

1. Constructive

2. Destructive

Constructive Interference

occurs when wave displacements are in

the same direction

the two waves pass through each other

without changing their shapes or sizes

the resultant pulse at the overlap of the

two waves is the algebraic sum

Constructive Interference

Destructive Interference

the superposition of waves with equal

but opposite amplitudes

when the pulses meet at the same

location, the displacement of the

medium is zero

just as constructive interference, the

waves pass through one another

unchanged

Destructive Interference

Standing Waves

a wave pattern that remains in a

constant position

the result of reflection and wave

interference

characterized by two fixed points on the

wave

Tacoma Narrows Bridge

In an effort to save money, corners were

cut in the design of the bridge thus

compromising its stability

On November 7, 1940 the Tacoma

Narrows suspension bridge collapsed

due to 42 mph wind induced vibrations.