2926: Doppler Effect
| Doppler Effect |
 Title text: The Doppler effect is a mysterious wavelength-shifting phenomenon which seems to primarily affect sirens, which is why the 🚨 emoji is red. |
Explanation[edit]
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This explanation may be incomplete or incorrect: Created by an ALARMED BOT THAT GOES... - Please change this comment when editing this page. Do NOT delete this tag too soon. If you can address this issue, please edit the page! Thanks. |
In the second and third panels, Miss Lenhart talks about the strange noise sirens (and cars) make when the pass you. The usual explanation of Doppler effect is that this noise is created because the sound waves are compressed in front of the car due to it traveling in the same direction of the waves, similar to a bullet fired forward from a car. The compressed waves create a louder, higher pitched sound, then as the car passes, the noise gets considerably softer and lower. The latter is because the waves are now being stretched out as they are moving in the opposite direction of their "creator", like a gun shot backwards from a car. However, Miss Lenhart doesn't make this usual explanation and instead starts talking about how cool sirens are.
Redshift is the same concept applied to wavelength of light and stellar objects. Red has longer wavelength than blue, and stars gets red when they move away from us and blue when they move towards us. We usually talk about redshift and not blueshift because while stars in our galaxy can move in any direction, the other galaxies are all moving away from us, and in fact they are moving quicker the father away they are, due to universe expanding. Note that unlike the usual explanation of redshift for sirens, a major component the red shift of light from distant galaxies is due to the expansion of space the light passing through while the light is in transit, rather than just the relative motion of the source and observer. This effect is not an important component of the Doppler shift for sirens.
The title text explains that the Doppler effect particularly affects sirens. This isn't actually true,[citation needed] but it may seem like it because sirens are almost always the analogy given, as in Miss Lenhart's lecture. Then it claims that the emoji for sirens is red because they're associated with redshift. Actually, the emoji is a picture of the rotating light on top of emergency vehicles; these tend to be used in conjunction with sirens, and they're red because this color typically signifies danger or warning.
Transcript[edit]
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This transcript is incomplete. Please help editing it! Thanks. |
- [Miss Lenhart is pointing with a stick to a whiteboard with various scientific drawings and words, including but not only a graph.]
- Miss Lenhart: The more distant a galaxy is, the redder its light.
- Miss Lenhart: Why? Well, that's an interesting question.
- [Zoom in on Miss Lenhart.]
- Miss Lenhart: Ever notice how, when a siren is approaching, it sounds like Bweeeeeeeeee...
- [Zoom in on Miss Lenhart with her arms raised.]
- Miss Lenhart: ...but then it zooms past and goes Nyeeeeooooowww?
- Miss Lenhart: And sometimes they hit a button that makes it go Pyeew! Pyeew! really loud?
- [Miss Lenhart with her finger raised is standing in front of the whiteboard and holding the stick down.]
- Miss Lenhart: And in Europe they go Ooooeeeeooooeeee...
- Off-panel voice: So why are galaxies red?
- Miss Lenhart: Oh, no idea.
- Miss Lenhart: Anyway, another siren I like is...
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