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Thread: A ship, A Stone, A lake!

  1. #1 A ship, A Stone, A lake! 
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    A ship is in a lake carrying a relatively large stone.The stone is thrown in the lake water, and thus sinks.What specifically happens to the water level of the lake (taking the shore as the reference)?


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  3. #2  
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    I need to think on this


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    If we took the stone and attatched it to a rope and tied other end of the roap to the ship and sunk the stone, we would have change.

    It depends on the stones density. Does the stone have an air pocket, or a bunch of air pockets. This is unknown.

    So if the stone still weighed the same as it was sunk in the water, and pulled on the ship the water level would surely rise because the stone is displacing water while also extering a downwards force onthe boat which is displacing water.

    Now in any case the stone will sink, so the water level would rise while it was still attatched to the boat..

    However if we were to cut this roap and allow the stone to drop and release the force from the ship, the water level would drop in comparison to when the stone was hung by a roap.

    But as for comparing the water level between the ship carrying the stone out of the water, and the difference in water level when the stone is thrown overboard, its a tricky one.

    but I am going to say that the stone is more effective at displacing water while placed in the boat than it is after being tossed overboard into the lake by itself. I am going with this reason because, the density of a stone is generally high, therefore the mass or weight of a stone can be large for a considerably small volume of rock, thus it should be more effective at using its gravitational weight to raise water level than it is at using its volume.



    So to conclude in the most normal of cases, I would have to say it is most likely that, if you tossed the stone overboard the water level would actually drop.

    But this goes with several assumptions. Since we dont know if there is a possible variable in the ship, or the stone.
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  5. #4  
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    I agree with arkain101. It's safe to assume the average density of the stone is larger than the density of water. Hence, it would sink when thrown overboard and would displace only its own volume in water. Sitting in the boat and thus forced to swim, the stone's effect is to displace its own mass in water (which is more than the stone's volume), according to Archimedes.

    Needless to say, the change of water level will be too small to measure on a lake, unless you have a huge boat and stone.
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  6. #5  
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    Imagine for a moment the stone is a 1cm cube but weighs 1 TON, when in the boat, the boat will displace an extra ton of water [1 cubic metre or so] remove the stone and drop it into the water where it will only displace 1CC of water.

    If the stone is denser than the water then chucking it overboard will raise the level, otherwise it will stay the same.
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    Forum Professor captaincaveman's Avatar
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    it would displace its own voulume in water, minus the difference in the boats boyancy(now stone is removed)eg it would be further out of water and therefore displacing less water :-D
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    Forum Ph.D. william's Avatar
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    I think the water level would drop since the stone sinks.

    Cheers,
    william
    "... the polhode rolls without slipping on the herpolhode lying in the invariable plane."
    ~Footnote in Goldstein's Mechanics, 3rd ed. p. 202
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  9. #8  
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    Billco, your example is good, but rethink your conclusion. What does it mean to "displace" water in a pool of fixed size? Displace a lot of water and the water level is high, displace just a little and the water level is low. The water level will drop as the dense stone is removed from the boat.
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  10. #9  
    Forum Professor captaincaveman's Avatar
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    Quote Originally Posted by M
    Billco, your example is good, but rethink your conclusion. What does it mean to "displace" water in a pool of fixed size? Displace a lot of water and the water level is high, displace just a little and the water level is low. The water level will drop as the dense stone is removed from the boat.

    wont removing the stone from the boat mean that the boat will displace less water as it doesn't sink as far into the water?
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  11. #10  
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    Quote Originally Posted by M
    Billco, your example is good, but rethink your conclusion. What does it mean to "displace" water in a pool of fixed size? Displace a lot of water and the water level is high, displace just a little and the water level is low. The water level will drop as the dense stone is removed from the boat.


    Yeah I got it right in my first sentence then said the opposite in my second. Think it's one of those times when you think about it both ways then cock it up.

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  12. #11  
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    wont removing the stone from the boat mean that the boat will displace less water as it doesn't sink as far into the water?
    You got it, ... that's the point.
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  13. #12  
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    Hey Billco,

    how can you have added 1300 posts in less than 3 months? Is this a full-time position for you? How much are they paying you? :-D
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  14. #13  
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    Quote Originally Posted by M
    Hey Billco,

    how can you have added 1300 posts in less than 3 months? Is this a full-time position for you? How much are they paying you? :-D
    S'easy just retire, break a bone in your foot and sit at the PC all day watching NASA TV and play the forum game. (almost better, it'll be bye bye when I am!).
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  15. #14  
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    Sorry about your foot. Although, you seem to take it well.
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  16. #15  
    Forum Professor captaincaveman's Avatar
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    Quote Originally Posted by billco
    Quote Originally Posted by M
    Hey Billco,

    how can you have added 1300 posts in less than 3 months? Is this a full-time position for you? How much are they paying you? :-D
    S'easy just retire, break a bone in your foot and sit at the PC all day watching NASA TV and play the forum game. (almost better, it'll be bye bye when I am!).
    my wifes always on live streams on nasa tv, there or the sky at night forums :-D
    CAPTAINCAVEMAN


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  17. #16  
    Cooking Something Good MacGyver1968's Avatar
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    My guess is that the water level would remain the same....but that's just a guess.

    Sorry to hear about your foot Billco, I told you about kicking "them damn whipper-snappers". Next time, just shake your cane at them. :wink:
    Fixin' shit that ain't broke.
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  18. #17  
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    Quote Originally Posted by captaincaveman
    Quote Originally Posted by billco
    Quote Originally Posted by M
    Hey Billco,

    how can you have added 1300 posts in less than 3 months? Is this a full-time position for you? How much are they paying you? :-D
    S'easy just retire, break a bone in your foot and sit at the PC all day watching NASA TV and play the forum game. (almost better, it'll be bye bye when I am!).
    my wifes always on live streams on nasa tv, there or the sky at night forums :-D
    Get youreslf a small planetarium and project it on the bedroom ceiling, that should help with your problem.... :wink:

    Quote Originally Posted by MacGyver1968
    My guess is that the water level would remain the same....but that's just a guess.

    Sorry to hear about your foot Billco, I told you about kicking "them damn whipper-snappers". Next time, just shake your cane at them. :wink:
    It happened in a hardware store, not my fault. (yes I am suing).
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