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Category: Science
Date: 10/13/12 07:00 AM

23 Responses to How Much Does A Shadow Weigh?

  1. Profile photo of uatme
    uatme Male 18-29
    1074 posts
    October 11, 2012 at 5:36 am
    Link: How Much Does A Shadow Weigh? - More than I thought (well less).
  2. Profile photo of Tiredofnicks
    Tiredofnicks Male 30-39
    5097 posts
    October 13, 2012 at 5:54 am
    Haven`t watched it, but I think I know the answer; a shadow is the absence of light, therefore "weighing" less than the surrounding area.
  3. Profile photo of auburnjunky
    auburnjunky Male 30-39
    10339 posts
    October 13, 2012 at 7:37 am
    There was an interesting question in that video.

    If I make a board a light year long, and push it to push a button on the other end, it would take 900,000 years to push the button, because my push only travels at the speed of sound.

    Huh?
  4. Profile photo of patchouly
    patchouly Male 40-49
    4746 posts
    October 13, 2012 at 7:42 am
    Another great science video here on I.A.B.! Thanks uatme!
  5. Profile photo of patchouly
    patchouly Male 40-49
    4746 posts
    October 13, 2012 at 7:46 am
    auburnjunky:
    "There was an interesting question in that video.

    If I make a board a light year long, and push it to push a button on the other end, it would take 900,000 years to push the button, because my push only travels at the speed of sound.

    Huh?"
    -------------

    With a board that long, when you pushed the one end, the "ripple" of that push would move along and take 900,000 years to reach to other end. As he explains in the video, the objects we push, here on Earth, are very small so the results of pushing a board seem instantaneous. In fact, there is an imperceivably small hesitation on the other end. A hesitation that, when magnified billions of times, becomes quite large.
  6. Profile photo of patchouly
    patchouly Male 40-49
    4746 posts
    October 13, 2012 at 7:47 am
    Remember, auburnjunky, objects are not solid but made up of particles with spaces in between.
  7. Profile photo of Tiredofnicks
    Tiredofnicks Male 30-39
    5097 posts
    October 13, 2012 at 8:16 am
    About the board, how fast the push gets there all depends on what material it is made of, "sound" or compression waves travel at different speeds in different media.
  8. Profile photo of auburnjunky
    auburnjunky Male 30-39
    10339 posts
    October 13, 2012 at 8:26 am
    Right tiredofnicks. Like, if it were made of Titanium, or some other hard material. Like diamond.

    I know it`s not feasible.
  9. Profile photo of pumba62
    pumba62 Male 40-49
    1018 posts
    October 13, 2012 at 9:27 am
    so ...I way more when the lights are on ?
    If the light emits from below does that make me lighter , because it would push up !
  10. Profile photo of auburnjunky
    auburnjunky Male 30-39
    10339 posts
    October 13, 2012 at 9:29 am
    @pumba:

    It`s "weigh" first of all.

    Secondly, light doesn`t push up per se. It surrounds and falls all over you, making you heavier.
  11. Profile photo of patchouly
    patchouly Male 40-49
    4746 posts
    October 13, 2012 at 9:30 am
    I`m not sure if the duration of time would be altered by the density of the material in question.

    I`d explain it like this. Picture a long line of magnetic marbles. When you push one toward the other, the second one is repelled and pushed into the third which in turn repels the fourth etc. While the time it take for the marble to travel into the other marbles magnetic field, and influence it, is very small, it would be measurable. Now, scale that down into the atomic scale and, instead of several marbles, imagine trillions and trillions of them, all lined up in a row. The "wave" you`d create by pushing the first marble would take a very long time to reach the end of the line. Same rule applies when it`s particles in a board of wood or a diamond. More marbles means the wave would travel quicker but take the same amount of time to reach it`s destination.

    Of course...I haven`t given this much thought so I very well could be wrong.
  12. Profile photo of patchouly
    patchouly Male 40-49
    4746 posts
    October 13, 2012 at 9:33 am
    auburnjunky:
    "Secondly, light doesn`t push up per se. It surrounds and falls all over you, making you heavier."
    -------

    That`s not correct, auburnjunky. It does in fact "push" you. Light is a particle/wave that carries energy. When it hit`s your body, some of that energy would be lost and it would be "pushing" you. So, to answer pumba62`s question, yes; if the light was below you, you would weigh less as it would be slightly lifting you up.
  13. Profile photo of chalket
    chalket Male 50-59
    2712 posts
    October 13, 2012 at 10:21 am
    patch "I`m not sure if the duration of time would be altered by the density of the material in question."

    Using your own analogy, wouldn`t your magnetic marbles push each other at different speeds in different media? If they are in viscous oil, they would push much more slowly than in air, or water, no?
  14. Profile photo of Tiredofnicks
    Tiredofnicks Male 30-39
    5097 posts
    October 13, 2012 at 10:24 am
    Patchy: You ARE wrong. ;)

    I`m not quite sure about the details and I can`t create fancy examples like yours, but I can post a link to someone who can:

    The speed of sound in other materials
  15. Profile photo of patchouly
    patchouly Male 40-49
    4746 posts
    October 13, 2012 at 10:37 am
    Tiredofnicks:
    "Patchy: You ARE wrong. ;)

    I`m not quite sure about the details and I can`t create fancy examples like yours, but I can post a link to someone who can:

    The speed of sound in other materials"
    -------------
    Well, there you go.

    I hadn`t committed any effort into thinking about the problem. Good thing is though, my analogy with the magnetic marbles still stands up, even if the duration is influenced by the density.
  16. Profile photo of auburnjunky
    auburnjunky Male 30-39
    10339 posts
    October 13, 2012 at 11:46 am
    @Patch:

    The light would have to be concentrated, because if it hit you anywhere else, in any other direction, it would apply force there as well, right?

  17. Profile photo of turdburglar
    turdburglar Male 30-39
    4896 posts
    October 13, 2012 at 11:53 am

    Good post. Good change of pace for IAB. Lately it seems there is too much religious or left vs. right political flame war fuel.
  18. Profile photo of ferdyfred
    ferdyfred Male 40-49
    13631 posts
    October 13, 2012 at 12:24 pm
    More of this IAB!!
  19. Profile photo of patchouly
    patchouly Male 40-49
    4746 posts
    October 13, 2012 at 12:31 pm
    auburnjunky:
    "@Patch:
    The light would have to be concentrated, because if it hit you anywhere else, in any other direction, it would apply force there as well, right?"
    ---------

    Partially true. The reflected light would have lost a large amount of its energy, after hitting the surface it reflected off of. Consequently, the energy pushing down would be more than the energy pushing up. So, it would still be pushing you down.
  20. Profile photo of DuckBoy87
    DuckBoy87 Male 18-29
    3238 posts
    October 13, 2012 at 1:18 pm
    Yo` mama`s so fat, her shadow weighs 42 pounds!
  21. Profile photo of PizzaPits
    PizzaPits Male 18-29
    553 posts
    October 13, 2012 at 2:41 pm
    Cool post. Enjoyed it.
  22. Profile photo of kemic
    kemic Male 18-29
    164 posts
    October 13, 2012 at 3:43 pm
    I LOVE VSAUCE
  23. Profile photo of patchgrabber
    patchgrabber Male 30-39
    5812 posts
    October 15, 2012 at 8:04 am
    So, to answer pumba62`s question, yes; if the light was below you, you would weigh less as it would be slightly lifting you up.

    This is technically true, light does exert a force, but not at the same speed as the light, rather, with the same momentum as the light. The momentum (p) of a single photon of light is equal its energy divided by the speed of light (E = c p). So how much momentum does a beam of light carry? Well, suppose we shine a 100 Watt spotlight. We are producing 100 Joules of light energy per second. So every second we are giving that light a momentum of (100J)/(300,000,000m/s) = .00000033 kg m/s.

    NASA actually has plans for prototypes of a "solar sail" to push space probes out of the solar system using no propulsion other than that provided by reflected sunlight.

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