Physical Science Waves and Sound

cypriotcamelUrban and Civil

Nov 29, 2013 (3 years and 6 months ago)

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Physical Science

Waves and Sound



Lincoln High School

Mr. Lowery

Earth Science

2007
-
2008

(slightly modified for Integrated Science: Ms. Gall 2011)

When something moves back
and forth, up and down, or
side to side we say it
vibrates.

A vibration is a wiggle. When
this wiggle moves through
space and time it is a
wave.

Light and sound are both
vibrations that move
through space as waves.

Sound is the movement of
vibrations of
matter



through solids, liquids, or
gases

Sound can not travel through a
vacuum. It must have matter
to vibrate.

Light needs no matter
to
vibrate, and can travel
through a
vacuum

such as
space.


(a
vacuum

is a space without
matter)

Light is a vibration of electric
and magnetic fields.

Example: We see light from
the sun.



Amplitude

is the distance from
the midpoint to the crest or
trough of the wave.

Wavelength

is the distance from
one crest to the next one or
one trough to the next one.

Frequency

is the number of
complete vibrations that a
wave makes in a given period
of time, usually one second.

The unit we use to measure
frequency is
hertz (Hz)

The
period
of a wave is the time
it takes for one complete
vibration.

Formulas:

Freq = 1/period

Period = 1/freq

Wave Motion


Transporting
Energy


Wave speed


Speed is
related to frequency and
wavelength.

Formulas:

Wave speed = freq x
wavelength


Types of Waves


Transverse


Vibrations that are at right
angles to the direction of wave
travel


The direction of wave travel is
perpendicular to direction of the
vibrating source



Longitudinal


Direction of wave travel is
along the direction in which the
source vibrates


Vibrations are parallel to the
direction of energy transfer


Area where waves are close
together is a compression



The stretched region, between
compressions, is called a
rarefaction


Both compressions and
rarefactions together make up
the longitudinal wave


Sound travels in Longitudinal
waves


The wavelength of a sound
wave is the distance between
successive rarefactions


The molecules in the air
vibrates



Because sound travels by
making the molecules vibrate,
sound can not travel through a
vacuum such as space. It
needs a medium. Otherwise,
there are no molecules to
compress and stretch


Our subjective impression
about the frequency of sound
is described as pitch. A high
pitch sound like from a tiny
bell has a high vibration
frequency


Sound from a large bell has
low pitch b/c its vibrations are
a low frequency


The human ear can normally
hear pitches from 20


20,000
hertz


As we age, this range shrinks


Sound frequencies below 20
hertz are called infrasonic


Frequencies above 20,000 are
called ultrasonic.


What are some ways we use
ultrasonic waves?


Humans can not hear
infrasonic or ultrasonic waves,
but dogs and other animals
can


Sound can travel through air,
solid, liquid or gas


Many solids and liquids
conduct sound better than air


Examples: sound underwater,
ear to a railroad track

Speed of sound


Does vary by medium


In air, varies by temp and
conditions of the air


Travels approx 330 m/sec in
dry air at 0 degrees C




Speed increases with temp


travels faster in warmer air


In water speed is 4 times as
fast as in air


In steel, speed is 15 times as
fast as in air

Reflection


Reflected sound is called an
echo.


Rigid and smooth surfaces
reflect large amount of energy


Sort, irregular surfaces echo
less




The study of sound
characteristics is called
acoustics


A room with “good acoustics”
means the sound reflects well
to all areas of the room

Refraction


Sound waves bend when
parts of the wave travel at
different speeds.


This bending of sound is
called
refraction




Quiz.

Give your name, date, and hour.

Draw a diagram of a wave.

Label the crest, trough,
amplitude and wavelength.