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Posers and Puzzles

Posers and Puzzles

  1. Standard member PBE6
    Bananarama
    16 Mar '05 20:08 / 1 edit
    It seems that most problems presented on this forum are mathematical in nature, with word problems/lateral thinking problems coming in a close second, and chess problems bringing up the rear, funny enough. How about a physics problem or two?

    1. Monkey + pulley: A cheeky little monkey is hanging onto a rope that is attached to a pulley, and counter balanced on the other end with a monkey-shaped weight. Both the monkey and the weight are at the same height initially. What happens if the monkey starts climbing the rope?

    2. Revolving sprinkler: Everyone has seen revolving sprinklers that spin when the water comes out. Imagine one with two L-shaped arms on opposite sides of the central hub, both pointing clockwise (as viewed from above). When you turns on the water, it spins counterclockwise. What happens if you put this sprinkler under water, and THEN turn it on? Which way will it spin? (BTW, Richard Feynman once wrecked a physics lab trying to answer this question experimentally.)

    Bonus points for anyone that can link to video footage of an experiment demonstrating your answer! But you'd better be in the video, or else...
  2. 16 Mar '05 21:18 / 4 edits
    1) By conservation of angular momentum, the weight should stay at the same height as the monkey.

    2) Didn't Feynman address the question of what happens when you submerge a sprinkler that sucks water in?

    3) Why does a mirror appear to invert the left-right directions, but not up-down?

  3. Standard member PBE6
    Bananarama
    16 Mar '05 21:27
    Originally posted by THUDandBLUNDER
    1) By conservation of angular momentum, the weight should stay at the same height as the monkey.

    2) Didn't Feynman address the question of what happens when you submerge a sprinkler that sucks water in?

    Oops, I think you're right about question #2. Let's rephrase it your way.

    And the answer to question #1 sounds right to me. Can someone please kidnap a monkey and make this video thing HAPPEN?!?
  4. Donation Acolyte
    Now With Added BA
    17 Mar '05 10:47
    Originally posted by THUDandBLUNDER
    3) Why does a mirror appear to invert the left-right directions, but not up-down?
    Because we tend to be standing up when looking at mirrors; we think of people as being able to turn freely about a vertical axis, but not around other axes; and we think of left and right as being somewhat similar, whereas up and down are different (because gravity pulls downwards), as are forwards and backwards (because we can only see forwards). When you look at yourself in the mirror, you're seeing an image of yourself reflected back-to-front, but this is too drastic a transformation for your subconscious brain to recognise it as the most obvious explanation for what has happened. Instead, your decide subconsciously to interpret what you are seeing as a copy of yourself which has been rotated 180 degrees about a vertical axis (because that's something people can easily do to themselves) and then flipped left-right (because who cares about left vs right?). Try lying on your side whilst looking at a mirror, and you'll find your subconscious miraculously stumbles across the correct interpretation of what you are seeing.

    A spherically symmetric life-form would not understand your question, as it would correctly imagine that a mirror reflects things back-front (if you take 'forward' as 'towards the mirror', ie the direction in which the creature's attention is focused).