MOD 5  LECTURE 8                                                  DOPPLER

In this lecture you will learn:

DOPPLER EFFECT: SOUND
"The Doppler effect (or Doppler shift), named after Austrian physicist Christian Doppler who proposed it in 1842, is the change in frequency of a wave for an observer moving relative to the source of the waves. It is commonly heard when a vehicle sounding a siren approaches, passes and recedes from an observer. The received frequency is increased (compared to the emitted frequency) during the approach, it is identical at the instant of passing by, and it is decreased during the recession."

MOST easily heard when a fast moving train comes towards a stationary person at a RR crossing. The pitch of sound is higher as the train approaches, lower as it moves away
 

 


 
stationary
moving forward
mach 1
greater than mach 1 and faster than the speed of sound
http://www.gmi.edu/~drussell/Demos/doppler/doppler.html

 
DOPPLER EFFECT: "SEEING" SOUND WAVES
Here is example of how a sonic boom can be seen  and HERE  is a very good physics explanation
 

http://antwrp.gsfc.nasa.gov/apod/ap010221.html
DOPPLER EFFECT: EMS - THE DOPPLER LIGHT SHIFT
The same thing is observed in light reaching earth from other stars.

The spectrum is shifted towards the blue end when it is approaching earth

The spectrum is shifted towards the red when it is going away.


 
DOPPLER EFFECT: EMS - RADAR, WEATHER 

 
 
 
 
 

RADAR (Radio Detection and Ranging) 

Radar depends on waves of the EMS that move out, bounce off some part of the car and are bounced back to the collector that generates a report on the speed of the car, either approaching or leaving. 

"Radar is an object detection system that uses electromagnetic waves to identify the range, altitude, direction, or speed of both moving and fixed objects such as aircraft, ships, motor vehicles, weather formations, and terrain. The term RADAR was coined in 1941 as an acronym for radio detection and ranging.[1][2][3][4] The term has since entered the English language as a standard word, radar, losing the capitalization. Radar was originally called RDF (Radio Direction Finder, now used as a totally different device) in the United Kingdom."
wikepedia

RADAR can be any wave of the EMS altho it says "radio" in fact other shorter wavelengths are used. 
 


WEATHER AND DOPPLER

Spotting tornados

How to interpret doppler signatures click HERE

Go HERE for explantion of this

"Idealized output of wind velocities has analyzed by a Doppler radar which has a full coverage of targets over is domain. The value of velocities varies with angle of view of the beam as the radar its only noticing the radar component."

traffic radar
REVIEW QUESTIONS:

Draw a picture and explain the doppler affect on sound when a train is coming towards and going away from a person.
What causes a sonic boom?
Draw and explain red and blue shift in light reaching us from distant galaxies.
What kind of uses are doppler shifts in waves of the EMS?