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# Do You Have a Science Question for our Community?

Do You Have a Science Question for our Community?

One of our members Miz Abynaah wanted to know more about the Doppler Effect (http://goo.gl/KIOa6B). Mike Aben  wrote this terrific explanation below as well as sharing this great video by +Alt Shift X.

Mike Aben: The Doppler Effect

The Doppler effect occurs whenever an object emitting waves is moving.  The effect is observed with any waves (water, sound, light, etc).  The waves being emitted ahead of the object’s motion are compressed, which means they will reach an observer at a higher frequency than if the object was stationary.  The waves emitted behind the object are stretched out and will reach an observer at a lower frequency.

With sound waves, this affects the pitch of the sound heard.  For example, the sound of a car traveling towards you will be at a higher pitch than the sound of a car moving away from you.  With visible light, it is the colour of the light that is affected.  Lower frequency light is redder, while higher frequency light is bluer.  For the effect to be noticeable with light, the relative velocity of the object to the observer has to be very high.

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This post was chosen by Zuleyka Zevallos  for #SoG+CuratorsChoice  #physics   #science

## Join the Conversation

1. Parvez Khan

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2. chandra jibi Yuku by yo you opp opinions .79 pip e 8 IL

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3. Cool cool

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4. Sito good

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5. Can water start boiling at 4 degree centrigarade?

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6. The best!

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7. So nice think

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8. MARGARET NYAMBURA

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9. The thing people do

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10. My question is how am I gonna pass my physics exam this Monday? 😦

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11. Zamokwakhe Sishi The speed of light can be measured in the laboratory rather easily – no fancy equipment needed, just some spinning mirrors, a longish baseline, and some careful observation (read up on Fizeau’s mirrors) and you’ll get answers to a few % of the real value in vacuum.

The distances to stellar objects are calculated in a number of ways. You see, there are, in the universe, certain events that always yield a predictable result. For example, there are stars known as Cepheid variables. These stars slowly pulse – and their speed of pulsing depends on their mass only. So if you see a star, pulsing at a certain speed, then it must be a certain size (and thus, brightness). If the star seems rather faint, then it has to be farther away than if it seemed more luminous. Other examples are novae – they, we think, go ‘bang’ every so often, and the size of the explosion is expected to be constant. So if a nova goes off, and it looks rather faint, then it’s probably far away.

Check out the ‘cosmic distance ladder’ on wiki. Plenty of other examples there, but a great question! Thanks!

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12. Michael Copenhaver Yep – the sound wave bounces off the target, and depending on the speed of the listener, then there may be a Doppler shift or not.

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13. mrityunjay shukla Yes.

Reduce the air pressure around the water, and it will boil. This can be easily achieved with a vacuum chamber and a mechanical pump.

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14. Thanks for sharing the Doppler Effect video, very interesting. Why do some people always have to write weird unrelated comments?

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15. Very interesting, thank you. If I learn just one thing new every day, then the day was worth my while.

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16. I love your explanation …..

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17. James Garry thanks, but still scratching my head

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18. What is “Basic Science “? Is it true that no one can invent “Basic science ” anymore?!

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19. Wow…!

But how can to the explein..

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20. Athanasios Karagiannis i first learned about the light color shifts red and blue, but it was so long ago, always thought it was a hubble discovery.

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21. Dan Corby

Okay, try this. The good ol’ double-slit experiment. Weak light source, two slits, screen: the usual.

The wavefunction that describes the photon, as it leaves the source, has a non-zero value at both slits. It’s just a function – a mathematical contrivance that depends on time, location, etc. This function is complex (has a real part and an imaginary part). So the function has a perfectly legit value inside either slit – but when you look at the screen, treating the two slits as sources, the complex parts of these two new functions leads to interference. And if you don’t muck with the slits, then a lovely interference pattern is seen.

But the minute you try to figure out where each photon went, the pattern is destroyed. Put a 50:50 mirror in one slot and a detector and you’ve constrained the wavefunction either to be zero valued or not. In either case, the pretty pattern goes to the single-slit blur.

I did this 25 years ago in my 3rd year physics practicals – awesome stuff.

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22. Zamokwakhe Sishi my guess is that on a large scale, you can calculate it, but of course, across a room, it is too tought to gague the speed. It takes 8 seconds for light to travel from the earth to the moon, so (distance in 8 seconds) can be raised to a LCD of one minute, or one hour for MPH.

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23. Yes that is right

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24. Tim McCulloch Eight seconds?

Last time I checked it was a ~2.5 second round-trip.

The speed of light, as I mentioned earlier, is easily measured, not calculated, using the Fizeau apparatus.

There’s a nice write-up here:

http://spie.org/x32833.xml

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25. Michael Copenhaver the waves would ricochet, for the most part. but the reflected energy, not sure how it would look

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26. Jacob Isaac i did the same, man. looking for questions to comment on. i havent watched the video yet, either – just exercising my brain to jog old info back into use.

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27. fratam junior i heard that when you think over a question, and find 2 answers, the first one is more likely to be right. Test this out with difficult questions, it might be true.

also, Sherlock Homes quote- eliminate the impossible, and that which remains, however improbable, must be true

good luck, and eat some brain food. fish is good for staying mentally sharp

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28. I like it

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29. איזה מגניב!!!!!!!!!!!!!!!!!!!!!!!!

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30. James Garry you are right, i was thinking the sun’s light takes 8 seconds. thanks for lmk

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31. Tim McCulloch Eight minutes to the Sun, another 8 to get back.

Luna’s almost nextdoor.

And Fizeau’s kit is still something a highschool kid could build.

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32. Awesome article Thank you!

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33. did not understand a word he said….

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34. I guess that makes sense…

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35. BLU..Falmoutph

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36. Wats da easiest way to undrstnd Doppler effect of sound

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37. There is a change in frequency and wavelength of waves with respect to an observer. Waves infront will be compressed hence high frequency.

While those at the back are stretched hence low frequency and high wavelength.

This explains why d car approaches an observer with high note of pitch than wen leaving.

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38. Guys why does water at the equator flow in opposite directions

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39. Yes awesome the way you demonstrate seriously gd

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40. I think teachers should use it to teach lessons to their students to learn about The Doppler Efect

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41. Doppler effect

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42. Frequency varies with spped

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43. Have any other video’s?

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44. I like the Doppler Effect! I am a physicist, and former/retired college professor at Wilberforce University, Ohio. I wrote a computer program for a problem on this subject. I could give velocities of a sound  source and a listener, stationary or moving, in given directions, along a straight line. Could print the two dimensional wave fronts of the source heard by the listener. I was getting beautiful two dimensional printouts, Loved It!

Let me hear from you about your views!

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45. I love physics…the frequency of sound changes as an object moves away from you.

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46. Ya jafari sir there have relationbetween

Relative velocity & frequency

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