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I'd like to know how it'd be possible to calculate the pressure inside a plastic bottle filled with water and squeezed by say 20 kg sitting on the bottle, which is lying on its side (so that resistance to deformation does't come to play as much as it'd if it was sitting on a standing bottle).

Thank you

Charles

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Since you know the force on the bottle (roughly 200N), you would have to get an approximate area over which this force is distributed. You could try by spreading some ink on either the bottle or the weight to estimate the contact area. While this is not completely correct (the wall of the bottle does redistribute the pressure on the outside to a larger area on the inside), it should give a reasonable estimate to maybe a factor of two or so (but that's a guess of mine, of course). If you want to do it right, connect a long plastic pipe to the bottle cap and measure the height of the water column that gets squeezed out. That's a direct and fairly reliable pressure measurement. Lacking such a measurement, you could estimate from the squirt height. I am sue there are better ideas, still, but these are the easy ones that I can think of of the top of my head.

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  • $\begingroup$ I like these suggestions. I would add that the rigidity of the bottle will influence the "weight/area" calculation but +1 for the suggestions to measure either squirt height or capillary displacement as moderately easy way to get close to an answer - there is no exact solution without a LOT of additional information... $\endgroup$
    – Floris
    Commented Oct 14, 2014 at 2:49
  • $\begingroup$ I think the estimation using the contact area may be way off, too. On the other hand, "attach a pressure meter" is not very imaginative, is it? It might be an interesting experiment to compare multiple methods. $\endgroup$
    – CuriousOne
    Commented Oct 14, 2014 at 5:06

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