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Today I learned

  1. Jul 27, 2016 #1641
    Today I experienced or understood not knew or learned how young fresh girls' acts and words can change a straight man's mind completely. It's the power of lust or sexual urge not love. And that does occur in life as always.
    So you! :biggrin: all physics ladies should always be aware of how and what your spouses are thinking and want.
     
  2. Jul 27, 2016 #1642

    Ibix

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    Yes.

    TIL two things. One, that snipping the URL out of the super-long URL that Google provides doesn't always reduce to the valid URL. Two, I should always check my links...
     
  3. Jul 27, 2016 #1643

    jim hardy

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    While raising teenage daughters i realized they are not very aware of it.
    It is very potent. Please be careful with it.
     
  4. Jul 27, 2016 #1644

    ProfuselyQuarky

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    Today I learned what Wellie Wanging is--pretty much a sport consisting of throwing boots as far as possible.
     
  5. Jul 27, 2016 #1645

    fresh_42

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    I'll have to scale up my font sizes. I misread this.
     
  6. Jul 30, 2016 #1646

    OmCheeto

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    Today I learned that humans emit black body radiation in the visible wavelengths. Though, it is at a rate too low to see.
     
  7. Jul 31, 2016 #1647
    I wonder if those fish that live 5 miles deep in the ocean with huge eyes could see it.
     
  8. Jul 31, 2016 #1648

    jim hardy

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    Well now -
    That explains "Women's Intuition" .

    Vive la difference !
     
  9. Jul 31, 2016 #1649

    1oldman2

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    Dang, that sounds contradictory o_O
     
  10. Jul 31, 2016 #1650

    Ibix

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    Not really. Your retina needs (from memory) ~20-30 visible light photons on one cell to trigger a detection event. So to form an image you need 20-30 photons on each light sensitive cell. Anything emitting at a lower rate is not really emitting detectably to an unaided human, although it may be technically emitting.
     
  11. Jul 31, 2016 #1651

    1oldman2

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    Proof things aren't as they always seem, Thanks, I had no idea about the sensitivity of the eye to individual photons. (I also learned a bit about black body radiation thanks to Om's post)
     
  12. Jul 31, 2016 #1652

    mfb

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    People can sense single photons

    At E/kT > 55, such an emission is incredibly rare, however. Nonthermal bioluminescence is a larger effect, but still tiny.
     
  13. Jul 31, 2016 #1653

    OmCheeto

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    That's pretty good from memory! But according to an article posted by John Baez, someone determined that single cells can be triggered by single photons, but a bunch of cells, 9 in his example, have to be triggered at the same time, or the signal is ignored. [ref: Can a Human See a Single Photon?, Original by Philip Gibbs 1996.]

    This whole thing got started yesterday when someone here at the forum asked about a body at room temperature, and I decided to try and answer the question. After 6 or so hours of trying to figure it out, and doing very suspicious maths, even for me, I decided not to engage in the thread. But in the end, I found that wiki listed a number that was very close to mine, so I decided to publish my findings.

    Om's very suspicious number: a 700 nm photon is emitted every 24 seconds from a square meter something at 98.6°F (310.15K) [source of original numbers]

    Wiki's mathy number: For example, a black body at room temperature (300 K) with one square meter of surface area will emit a photon in the visible range (390–750 nm) at an average rate of one photon every 41 seconds, meaning that for most practical purposes, such a black body does not emit in the visible range. [ref: wiki, Black Body Radiation, referencing: mathy stuff]
     
  14. Jul 31, 2016 #1654

    Jonathan Scott

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    On Thursday, I learned what it's like to ride a Segway PT. On our family vacation, we included a 45 minute "Segway Experience" riding X2s around, first getting to know how to operate it, then a quick obstacle course to make sure we were getting the hang of it, then they turned off the "turtle mode" beginner limiter and let us have half an hour charging along in single file around tracks and forest paths on the Center Parcs Elveden site where we were staying - all in the pouring rain with USAF jets from RAF Lakenheath thundering overhead (if it had been real thunder, they would have cancelled most of the outdoor activities).

    They insisted that we wear their supplied helmets, knee guards and elbow protectors, but there was nowhere to sit while putting on the knee guards and I managed to fall over trying to put one on, when it got caught on a shoe. In contrast, none of us fell over at all on the Segway, although I had a near miss when the left wheel took off over a tree root and landed at an angle ahead of the other wheel, after which I managed to zig and zag about six times before getting fully back in control.
     
  15. Jul 31, 2016 #1655

    Jonathan Scott

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    On Saturday, I learned a bit of Anglo-Saxon history. We visited Sutton Hoo, where there is an area of Anglo-Saxon burial mounds dating to the 6th and early 7th centuries, where an intact mound was found in 1939 with a ship burial, probably of the local king.

    I also visited Tranmer House, where the owner of the Sutton Hoo area lived. Several of the rooms have been set up to illustrate how it would have looked in the 1930s, around the time of the discoveries. In the main room, there was a grand piano by Schiedmayer of Stuttgart, from around 1864, which had been partly refurbished. I hadn't heard of that make before, but it was one of the most beautiful sounding pianos I have ever encountered and had been well looked after. I was invited to play it, and after I played a few bits of classical music from memory they found a book of Scott Joplin ragtime music, so I played The Entertainer and some of the others, which helped to wind back the clock a bit, although the use of it in the film "The Sting" to depict the 1930s is somewhat anachronistic, as it was only really popular until about 1911.
     
  16. Jul 31, 2016 #1656

    OmCheeto

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    Today I learned, that if you leave a black rock out in the sun, it won't get hotter than 196°F. (sans local reflective sources)
    (strictly from theoretical maths, and stuff from wiki, of course.)

    But this brought to mind, "It's so hot, you can fry an egg on the sidewalk!"

    Which from my calculations, and semi-infinite knowledge of properly cooking turkeys, a 196°F sidewalk should very properly cook an egg.

    Which of course led to me googling, and finding: Death Valley employees beg visitors to stop frying eggs on the sidewalk
     
  17. Jul 31, 2016 #1657

    Ibix

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    My memory is faulty. According to section 5 of http://webvision.med.utah.edu/book/...nd-cones/phototransduction-in-rods-and-cones/, that rods could react to single photons has been known experimentally as far back as 1979, and was inferred by Hecht et al as far back as 1942. My number is more consistent with Hecht's "seeing curves" (figure 4B in the link) which are a measure of how many photons you need to be able to see a flash, rather than how many you need for a photoreceptor to respond. Although mfb's article suggests even that has been superceded.
    I suspected as much but had not done the maths.
     
  18. Jul 31, 2016 #1658

    OmCheeto

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    I had my head in my oven yesterday, with my laser thermometer pointed at the heating element, trying to capture the temperature that my eyes could see it start glowing. It was around 600°F.
    Though, I knew that the heating element was some non-perfect, non-homogenous creation, so I thought to myself; "hmmmm.... Who routinely looks at glowing hot stuff, and would know the temperatures?"
    I ended up at a ceramics website, where they claimed that pottery starts visibly glowing at around 700K.
    From that, I determined that our eyesight was about 10 quadrillion times too weak to see our "human" glow.

    ps. But as I mentioned above, I find all of my calculations very suspicous, as this is all very new to me.
     
  19. Jul 31, 2016 #1659

    mfb

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    You probably watched it in daylight or at least with other light sources nearby (and with a visible laser pointer?). You'll get better results if you switch off all light sources and wait a few minutes. The single-photon tests had the test persons sit in absolute darkness for 40 minutes.
     
  20. Jul 31, 2016 #1660

    ProfuselyQuarky

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    Today I learned how to properly temper chocolate. Watch out, Benoit Blin.
     
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