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Demonstrating crush depth?

  1. Jul 11, 2017 #1
    I'd like to rig up a glass pressure vessel to see if I could demonstrate crush depth and stuff like that. I was sort of picturing a large small-necked glass jug (think water cooler jug) filled with water and attached to a compressor (or maybe even bike pump?). Styrofoam objects would be inserted, weighted down so they are suspended near the middle of the water, the top sealed, the vessel pressurized, etc...
    I've seen demos like this done with Styrofoam beads in a plastic bottle filled with air pressurized with a bike pump. Since liquids aren't compressible, would filling the glass container with water first make it impossible to reach sufficient pressure?
    Thoughts?
    Safe?
    Fittings?
    Could enough pressure be generated with a bike pump?
     
  2. jcsd
  3. Jul 11, 2017 #2
    "Rigging up" something to demonstrate "crush depth" with Styrofoam is not safe.
    You need to use known pressures, equipment that is rated for those pressures, and procedures for maintaining and operating that equipment that are well thought out.

    A quick web search shows you can do this safely with a pressure cooker.
     
  4. Jul 11, 2017 #3

    berkeman

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    Staff: Mentor

    Why use glass? Just use a plastic jug with weights, and lower it into the school pool to show how it crushes when filled with air, but does not crush when filled with water...
     
  5. Jul 11, 2017 #4
    Thanks .Scott for the quick reply. I know fiddling around with pressurized containers isn't the safest. I wasn't sure how high the pressure would need to be to achieve measurable results on something like a styrofoam cup. The demo needs to be visible which is why I thought a large relatively thick glass jug would work.I have seen demos like this that use styrofoam beads in a plastic water bottle pressurized with a bike pump but wondered if filling with water would be doable.
     
  6. Jul 11, 2017 #5

    berkeman

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    Staff: Mentor

    Oh, I misread your post. You want to pressurize a glass jug. I agree with @.Scott that is a bad idea. Don't you have a pool available?
     
  7. Jul 12, 2017 #6
    Nope. No pool available. I'm trying to sort of duplicate that demo we've all seen where a styrofoam cup is attached to the outside of a submarine. The sub dives and returns to the surface. When the sub returns to the surface the cup has shrunk due to the pressure at depth.
    I'd like to build an apparatus to demonstrate this as part of an installation on a submarine at a museum. I picture kids decorating their little cups and then placing them in the vessel which seals (autoclave or pressure cooker style) and they watch as pressure is increased till the cup (which is visible) begins to compress. The vessel opens and the kids have a souvenir and hopefully some interest in finding out more.
     
  8. Jul 12, 2017 #7
    The results from 2000 psi:
    cups_545.jpg
    http://oceanexplorer.noaa.gov/explorations/deepeast01/logs/sep14/media/cups.html

    Even at half that pressure, an unplanned release could sent you pressure vessel rocketing across the room.
     
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