Editing 2926: Doppler Effect
Warning: You are not logged in. Your IP address will be publicly visible if you make any edits. If you log in or create an account, your edits will be attributed to your username, along with other benefits.
The edit can be undone.
Please check the comparison below to verify that this is what you want to do, and then save the changes below to finish undoing the edit.
Latest revision | Your text | ||
Line 10: | Line 10: | ||
==Explanation== | ==Explanation== | ||
− | + | {{incomplete|Created by an ALARMED BOT THAT GOES... - Please change this comment when editing this page. Do NOT delete this tag too soon.}} | |
− | |||
− | |||
− | + | [[Miss Lenhart]] is teaching a class about the concept of {{w|redshift}} and using the {{w|Doppler effect}} as a demonstration. The comparison begins as relevant, but then quickly becomes extraneous when she brings up the "BUTTON THAT MAKES IT GO PYEEW! PYEEW!". In fact, it seems she cares more about her special interest in various emergency vehicle sirens than about astronomy, the field in which she teaches. | |
− | + | 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 the source of the sound waves is moving. Consider a sound being generated at a frequency of 1000 cycles per second (Hertz); each wave will propagate at a fixed speed in the air, the speed of sound. The car generates peak A, which begins moving away at the speed of sound, and 1/1000th of a second later, generates peak B, which also begins moving away at the speed of sound. In that 1/1000th of a second between peaks being generated, the car has traveled slightly forward, so peak B is produced slightly farther along the car's direction of travel than the previous peak. For an observer in front of the car, because peak B was generated a bit closer to the observer, they would measure (hear) a shorter wavelength (higher pitch) than if the peaks were generated from a stationary car. Similarly, for an observer behind the car, because peak B was generated a bit further away, they would hear a lower pitch. 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 | + | The title text explains that the Doppler effect particularly affects sirens. This isn't actually true,{{cn}} 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== | ==Transcript== | ||
− | :[Miss Lenhart is pointing with a stick to a whiteboard | + | {{incomplete transcript|Do NOT delete this tag too soon.}} |
+ | |||
+ | :[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: The more distant a galaxy is, the redder its light. | ||
:Miss Lenhart: Why? Well, that's an interesting question. | :Miss Lenhart: Why? Well, that's an interesting question. | ||
:[Zoom in on Miss Lenhart.] | :[Zoom in on Miss Lenhart.] | ||
− | :Miss Lenhart: Ever notice how, when a siren is approaching, it sounds like '''' | + | :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 | + | :Miss Lenhart: ...but then it zooms past and goes ''Nyeeeeooooowww?'' |
− | :Miss Lenhart: And sometimes they hit a button that makes it go | + | :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 | + | :Miss Lenhart: And in Europe they go ''Oooo<sup>eeee</sup>oooo<sup>eeee...</sup>'' |
− | :Off-panel voice: So | + | :Off-panel voice: So ''why'' are galaxies red? |
:Miss Lenhart: Oh, no idea. | :Miss Lenhart: Oh, no idea. | ||
:Miss Lenhart: Anyway, another siren I like is... | :Miss Lenhart: Anyway, another siren I like is... | ||
Line 44: | Line 44: | ||
[[Category:Comics featuring Miss Lenhart]] | [[Category:Comics featuring Miss Lenhart]] | ||
[[Category:Physics]] | [[Category:Physics]] | ||
− | |||
− |