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Thread: conceptual question

  1. #1 conceptual question 
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    if you place a cube in water then you cut the cube into half and place it into water of the same temperature assume temp of water is constant.which cube the bigger or the smaller will experience a greater drop in temperature.


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  3. #2  
    Forum Ph.D. Nevyn's Avatar
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    not sure what you are on about, do you mean Ice cubes?


    Come see some of my art work at http://nevyn-pendragon.deviantart.com/
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  4. #3 Re: conceptual question 
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    Quote Originally Posted by myoplex11
    if you place a cube in water then you cut the cube into half and place it into water of the same temperature assume temp of water is constant.which cube the bigger or the smaller will experience a greater drop in temperature.
    Assuming the cube's temperature is lower than that of the water, the smaller, of course. There's less distance for the heat to travel.
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  5. #4  
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    The same. *Assuming a large volume of water, both cubes will equilibrate at the water's temperature. The cube's temperature drop (but not heat loss) will be the same for each cube.
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  6. #5  
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    Quote Originally Posted by SteveF
    The same. Assuming a large volume of water, both cubes will equilibrate at the water's temperature. The cube's temperature drop (but not heat loss) will be the same for each cube.
    Why not the heat loss too, Steve?

    Oh, I see. You assumed only half the cut cube went into the water.
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  7. #6  
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    Quite correct, Harold. Myoplex wanted results for "which cube the bigger
    or the smaller... "

    I hope he isn't confusing temperature with heat.
    They are not the same.
    *
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  8. #7  
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    Let me re-phrase this question the way I understand it (the only way it makes sense as a homework problem):

    I have two cubes of equal size, equal homogenous material, and equal temperature Tc, and two very large reservoirs of water at uniform temperature Tw, lower than Tc. I drop one cube into reservoir 1. At the same time I cut the second cube into two halfs, and drop those into reservoir 2. Which of the cubes, the whole one, or the one cut in half, will cool down faster, and why?
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  9. #8  
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    My money is on the two split ones - and it all boils down to the extra surface area for heat transfer you have allowed by cutting the block in two.
    As is often the case with technical subjects we are presented with an unfortunate choice: an explanation that is accurate but incomprehensible, or comprehensible but wrong.
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  10. #9  
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    There you go. It was an easy problem after all.
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  11. #10  
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    Here's another easy(?) one: I make 2 cups of tea. I add milk to one immediately, and an equal quantity of milk to the other some (reasonably short) time later . If I measure the temperature of each at some (reasonably short) time later, which is the cooler? Milk first or milk second? No difference? Why?
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  12. #11  
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    Post deleted by Farsight.
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  13. #12  
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    Quote Originally Posted by Guitarist
    Here's another easy(?) one: I make 2 cups of tea. I add milk to one immediately, and an equal quantity of milk to the other some (reasonably short) time later . If I measure the temperature of each at some (reasonably short) time later, which is the cooler? Milk first or milk second? No difference? Why?
    Your best strategy for cooling the tea is to wait a bit before adding the milk. Assume the milk is at room temp or kept in the fridge until just before adding, then it is not gaining or losing heat. Assume also that the surface area of the cup heated by the tea is not significantly increased by the milk addition. Then the rate at which heat is dissipated is proportional to the delta-T between the tea and ambient. So therefore the most heat is dissipated by keeping the temperature up longer.
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