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Thread: Logic Q

  1. #1
    amina_imen is offline Former Member
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    If you like mental acrobatics, have a go at this.
    [list=1][*]If you stand behind a pillar and speak, a person on the other side can hear you clearly. However, if you shine a flashlight the person on the other side will not be able to see the flashlight !! (Assuming there's no dust in the air, or something else around to reflect it). Light and sound being waves, you'd expect them to travel in straight lines. So how come you can `hear the voice' but not `see the light'?
    [*]Why does water go down the drain clockwise in the northern hemisphere, and anticlockwise in the southern hemisphere? [/list=1]

  2. #2
    Shotokan_Karate is offline Registered User
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    Salaam Amina,

    mmmm...very interesting! I'm still thinking about them.

    I knew about the second one but I don't know yet the reason why that happens

    ??


  3. #3
    Shotokan_Karate is offline Registered User
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    For the first one I would have thought that light and sound travel differently from each other.

    The photons of light travel in the form of radial waves i.e. in straight lines from the source of the light to the first object it encounters and that's where that portion of light stops (examples: day and night, phases of the moon) ; whereas sound travels in the form of concentric circles (with the aid of vibration) from the source and therefore surrounds the objects it encounters.

    Am I at least close??


  4. #4
    amina_imen is offline Former Member
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    For the first one I would have thought that light and sound travel differently from each other.

    The photons of light travel in the form of radial waves i.e. in straight lines from the source of the light to the first object it encounters and that's where that portion of light stops (examples: day and night, phases of the moon) ; whereas sound travels in the form of concentric circles (with the aid of vibration) from the source and therefore surrounds the objects it encounters.

    Am I at least close??

    Shotokan salam,

    I thought nobody would have a go at the questions

    For the first one, hmm that's because of the wavelength of light. If you remember the experiment from high school/college (Young's two slit experiment), it
    showed that diffraction is typically observable when the size of the obstacle is comparable to the wavelength.

    Light has wavelength in nanometers -- much smaller than the size of the pillar, so no diffraction occurs. Sound has wavelength comparable to the size of the pillar, and actually diffracts 'around' the pillar, which is
    why you hear it (and don't see the light)!

    I might have interchanged northern and southern in the
    question, so thinking about it again it should be 'anti-clockwise in the northern hemisphere and clockwise in the southern hemisphere'

    Just think about earth's rotation!


  5. #5
    Shotokan_Karate is offline Registered User
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    Salaam Amina,

    Thanks for the trip down memory lane I don't remember a thing! Got to refer back to my dusty old textbooks

    Taking your clue into consideration, it seems to me that the water just follows the rotation of the earth. So the direction does not change but our position in relation to it does (i.e. northern or southern hemisphere) Take the example of a spinning wheel; if, looking from above it's rotating anticlockwise then, looking from underneath, it will appear to rotate clockwise. Is it really as simple as this?


  6. #6
    amina_imen is offline Former Member
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    Shotokan, salam

    Well, I won't type out a complete answer here (because that needs a picture, and a fair amount of explanation, also because I think you -almost- got it). But the short story is this:

    Because of the earth's rotation, any moving body gets deflected to its right in the northern hemisphere, and to its left in the southern hemisphere (visualise it, and you should be able to figrue out why).

    Now, when water is trying to flow into the drain in the northern hemisphere, and it gets deflected to its right, it goes down counter clockwise.

    Similarly in the southern hemisphere, deflection to the left makes it go down clockwise!

    I think you got the answer, I'm just not sure!

    How is Ramadhan with you Shotokan?

    Take care


  7. #7
    Shotokan_Karate is offline Registered User
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    Salaam Amina,

    Yes, more or less that's what I had in mind. But now I'm confused!!! Because I searched for it on the net and most of the explanations say that it's not true!!!

    Here's one of them for example:

    http://www.newton.dep.anl.gov/askasc...0/phy00689.htm

    There is logic in it I must say but what do you think?



    Ramadhan is going well for me alhamdulillah. How about you?

    Oh! tell me...did you break the step machine yet?


    Take care you too!

    Salaam


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