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The Doppler Effect- Physics Final Project

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Christina Mazzio

on 17 June 2013

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Transcript of The Doppler Effect- Physics Final Project

Christina Mazzio
The Doppler Effect
named after Austrian physicist Christian Doppler (1803-1853)

"Concerning the colored light of the double stars and certain other stars of the heavens"
his theory...

in this presentation...
real-life applications
have you ever noticed
how the pitch of a police car
siren is higher as it approaches you and lower after it passes by?
if you answered yes, then you have witnessed the Doppler Effect!
this effect describes the
high pitch
low pitch
in this paper, Doppler developed a theory which he hoped astronomers of the future could use to measure the movement and distance of stars
Doppler, a mathematics professor at the Technical Institute of Prague, presented his paper
apparent change in frequency

between waves leaving a source and reaching an observer
this apparent change is dependent on the
relative motion

between the wave source and observer
at a meeting of the Natural Sciences Section of the Royal Bohemian Society in 1842
waves in front of a moving source are compressed while waves behind a moving source are stretched out
take a look at this train moving toward the right...
waves that are farther apart have
lower frequency and
lower pitch
waves that are closer together have
higher frequency and
higher pitch
in 1845, Doppler decided to test his theory with sound waves from trumpets
he had two groups of trumpeters play the same note, only one group played from a train car and the other from the train station
the notes were
(meaning they had different frequencies), proving Doppler's theory to be true
although Doppler mentioned light in his theory, it was impossible for scientists of the time to test it out, so he focused on sound waves instead
as the group in the train passed and moved further from the station, it sounded as though two different notes were being played
Police Radar
this video from YouTube is a modern version of Doppler's experiment...
now let's see how the Doppler Effect is applied to our lives today
ever wonder how police know that you are driving over the speed limit?
the Doppler Effect is behind it all!
the radar speed detector bounces microwaves off of an oncoming vehicle and detects the
of the reflected waves
change in frequency

the difference in frequency is known as
beat frequency
and with this calculation, the radar determines the velocity of the vehicle
the following equation is the way velocity is found using beat frequency...
"v target" is the velocity of the target vehicle and is positive
beat frequency
Weather Radar
a Doppler radar is used to make weather predictions as well
this radar will send out beams in circular patterns at a constant rate
once the beams reach a raindrop, they are reflected back to the radar
the difference in frequency of the reflected beam allows the radar to calculate how far away the rain is, the direction it is moving in, and wind velocity
this process allows us to create the images we see on TV
look familiar?

this effect describes the
apparent change in frequency

between waves leaving a source and reaching an observer
this apparent change is dependent on the
relative motion

between the wave source and observer
determining how fast blood flow is using the Doppler Effect is very important in medicine
the Doppler Ultrasound is used similarly to a regular ultrasound only it is mainly used to identify if one has a circulatory problem, such as a blood clot
the gel placed on the patient's skin is used as a conductor of sound waves, which are used to create images of the area being tested
the machine bounces
(high frequency sound waves) off of circulating red blood cells and an estimate of how fast blood is flowing can be made by measuring the rate of change in the waves' pitch
this ultrasound is used to diagnose problems such as blood clots, heart valve defects, blocked arteries, aneurysms, and decreased blood circulation
not only has the Doppler Effect been used in people's everyday lives, it is also being used by astronomers to answer questions about the Universe and objects beyond Earth, just as Doppler predicted
as stars shift relative to us on Earth we can determine the directions they are moving in and how fast they are moving with the Doppler Effect and what we call
red shift
" and "
blue shift
red shift...
the star is
moving away

from the observer and the waves are farther apart
blue shift...
the star is
moving toward
the observer and the waves are compressed
since the waves are farther apart, there is a lower frequency and an apparent shift to the red end of the spectrum
red light has a lower frequency than blue
since the waves are compressed, there is a higher frequency and a shift to the blue end of the spectrum
blue light has a higher frequency than red light
Expanding Universe
by observing red shift, astronomers have been able to better understand the possible past and future states of the Universe
in 1929, Edwin Hubble, working in California, measured the red shifts of distant galaxies and their relative distances by measuring apparent brightness
Hubble graphed his results and found that redshift of the galaxies is directly related to their distance meaning that the
Universe must be
once this was understood, scientists soon realized that the Universe must have always been expanding and must have started out as one point, which we know as the Big Bang







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