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Looking for answers about my cartesian diver

  1. Aug 5, 2012 #1
    Hello all,

    I've got a quick question, I am sure it will be resolved by the first comment, but I'm just looking for a quick answer.
    I brought home a pipette from my mothers lab last week and made a cartesian diver to show my wife, it worked perfectly for about 3 days, then yesterday afternoon (about 1) I left my home, and turned the air up to about 85°, my wife and I returned home about 10 p.m. and I noticed that the diver was at the bottom of the bottle. :confused:

    My only guess is that the heat of the home caused the water to expand, but because it is trapped within the bottle, it had the same effect on the diver as the pressure applied from the outside. additionally, when I opened the bottle, some of the water squirted out, and the diver returned to the surface.

    Thanks for any info!
  2. jcsd
  3. Aug 5, 2012 #2
    I've not heard of a cartesian diver before, sounds fun.

    So I take it on the third day it was much hotter than the previous days? My best guess wold be the water would want to increase in volume with the increase in temperature (thermal expansion), but was constrained by the bottle, so its pressure increased. The air in the diver is compressible, so with the increase in water pressure the volume of the air in the diver reduces (and the pressure of the air increases too) so as you said, the diver sinks for the same reason as when you squeeze the bottle - more water in the diver. When you opened the bottle the water pressure normalised with the atmosphere and normal service was resumed. That would be my take, anyway. Is that what you were thinking too?
  4. Aug 6, 2012 #3


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    Could be expansion of the water but.. was there any air space at the top of the botle when you closed it? I reckon expansion of that air is more likely to blame for increasing the pressure.
  5. Oct 14, 2012 #4
    there was some air in the top, just enough to keep from making a mess when I closed it. Im not really clear on a lot of principles of pressure and such, that was a really weak point in my studies of chemistry and physics, but I cant imagine it was due to air expansion because there was a total lack of air in the bottle when I unscrewed the lid. its all very confusing to me.
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