User Tag List

Dislikes Dislikes:  0
Page 1 of 2 12 LastLast
Results 1 to 20 of 21

Thread: fwtk: physics, atmospheric pressure stuff.

  1. #1
    Member forunna's Avatar
    Join Date
    May 2014
    Location
    Darling Downs
    Motorbike
    Suzuki GN250
    Liked
    27 times
    Posts
    402
    Post Thanks / Like
    Mentioned
    0 Post(s)
    Tagged
    0 Thread(s)

    fwtk: physics, atmospheric pressure stuff.

    HEY,
    when you fill a glass with water then lift it partially out of the sink (upside down) and the water stays in, is the pressure up the top (inside) the same as atmospheric or is it less than atmospheric?
    I am thinking less, because i know you can only theoretically suck up to 10 meters high then you just pull a vacuum.
    Any body know?

  2. #2
    Member Crobbo's Avatar
    Join Date
    Mar 2010
    Location
    Not a Zero Hero
    Motorbike
    The lil tractor that could.
    Liked
    631 times
    Posts
    4,771
    Post Thanks / Like
    Mentioned
    47 Post(s)
    Tagged
    0 Thread(s)
    It would be less than atmospheric.
    Rules are for the guidance of wise men and the obedience of fools. - Sir Douglas Robert Steuart Bader

  3. #3
    Member
    Join Date
    Apr 2013
    Location
    Kardinya
    Motorbike
    CB250RS & ZRX1200R
    Liked
    78 times
    Posts
    639
    Post Thanks / Like
    Mentioned
    4 Post(s)
    Tagged
    0 Thread(s)
    Depending on how high you lift it the pressure will be current atmospheric pressure at your location in kPa - 9.81 * height of water in the glass in m * density of fluid (usually 1)...

  4. #4
    Member GsxInShed's Avatar
    Join Date
    Jun 2010
    Location
    Next to the big hole in the economy
    Motorbike
    (TY-250- RD350LC- Gsx 750 esd) Current -Gsx 250 SSM GSX 1100 EFE
    Liked
    304 times
    Posts
    6,460
    Post Thanks / Like
    Mentioned
    31 Post(s)
    Tagged
    0 Thread(s)

    It would seem . atm pressure is acting on the water in the sink.

    Surface tension is acting on the water in the glass.

    yet...the pressure should be less in the glass...( the bit that is occupied by air....in a decreasing pressure system..)

    'Cause you are creating a stand alone system' in the glass...

    Fkn lovely conundrum... bro ...cheers' :-)
    " Imagination is the seed of life..."

  5. #5
    Member agrid's Avatar
    Join Date
    Apr 2008
    Liked
    2779 times
    Posts
    14,107
    Post Thanks / Like
    Mentioned
    56 Post(s)
    Tagged
    0 Thread(s)
    Air weighs a bit, water weighs more.
    -

  6. #6
    Member GsxInShed's Avatar
    Join Date
    Jun 2010
    Location
    Next to the big hole in the economy
    Motorbike
    (TY-250- RD350LC- Gsx 750 esd) Current -Gsx 250 SSM GSX 1100 EFE
    Liked
    304 times
    Posts
    6,460
    Post Thanks / Like
    Mentioned
    31 Post(s)
    Tagged
    0 Thread(s)

    Quote Originally Posted by agrid View Post
    Air weighs a bit, water weighs more.
    Exactly how much, my learned friend..?

    ( a Kg of air weighs exactly the SAME as a Kg of water..) The differences , however are potentially enormous.
    " Imagination is the seed of life..."

  7. #7
    Member forunna's Avatar
    Join Date
    May 2014
    Location
    Darling Downs
    Motorbike
    Suzuki GN250
    Liked
    27 times
    Posts
    402
    Post Thanks / Like
    Mentioned
    0 Post(s)
    Tagged
    0 Thread(s)
    there is no air .
    was just discussing with a mate.
    he wants to do something he has seen. an inverted fish tank in his pond so fish can swim up into it.
    he is worried the reversd pressure will crush a normal fish tank. i am not sure the fish will like it anyway.
    we couldnt decide what was pressure where. so we just ended up discussing it all in general.

  8. #8
    Member forunna's Avatar
    Join Date
    May 2014
    Location
    Darling Downs
    Motorbike
    Suzuki GN250
    Liked
    27 times
    Posts
    402
    Post Thanks / Like
    Mentioned
    0 Post(s)
    Tagged
    0 Thread(s)
    Quote Originally Posted by GsxInShed View Post
    Exactly how much, my learned friend..?

    ( a Kg of air weighs exactly the SAME as a Kg of water..) The differences , however are potentially enormous.
    i would rather be hit by a tonne of air than a tonne of water.

  9. #9
    Member Crobbo's Avatar
    Join Date
    Mar 2010
    Location
    Not a Zero Hero
    Motorbike
    The lil tractor that could.
    Liked
    631 times
    Posts
    4,771
    Post Thanks / Like
    Mentioned
    47 Post(s)
    Tagged
    0 Thread(s)
    The fish won't give a shit. The only concern I would have is the top of the fish tower caving in under the vacuum of the water inside it.

    Have a play around with a container in your kitchen sink or bath. That should give you a good idea of what you're up against.

    There's also the weight of all the water you'll have to support.
    Rules are for the guidance of wise men and the obedience of fools. - Sir Douglas Robert Steuart Bader

  10. #10
    Member forunna's Avatar
    Join Date
    May 2014
    Location
    Darling Downs
    Motorbike
    Suzuki GN250
    Liked
    27 times
    Posts
    402
    Post Thanks / Like
    Mentioned
    0 Post(s)
    Tagged
    0 Thread(s)
    Quote Originally Posted by Crobbo View Post
    The fish won't give a shit. The only concern I would have is the top of the fish tower caving in under the vacuum of the water inside it.
    yes, hence my original post.
    i have experimented with a small fishtank in a horse trough. didnt implode or explode.
    i dont think the dimensions in question will really test the bounds of physics though.

  11. #11
    Member Para045's Avatar
    Join Date
    Oct 2006
    Location
    City of Wanneroo
    Motorbike
    98 TITANIUM CBR1100XX SUPERBLACKBIRD
    Liked
    1150 times
    Posts
    14,951
    Post Thanks / Like
    Mentioned
    62 Post(s)
    Tagged
    0 Thread(s)
    Quote Originally Posted by GsxInShed View Post
    Exactly how much, my learned friend..?

    ( a Kg of air weighs exactly the SAME as a Kg of water..) The differences , however are potentially enormous.
    Yeah but given the VOLUME of both inside the glass even if they are equal the weights will be different
    #1 Gold Ticket Holder for the Barfridge Fan Club
    Quote Originally Posted by Phildo View Post
    Noted. We'll check back on that one in three years
    Quote Originally Posted by filbert View Post
    i'll pretend you didn't know she was 13

    98 BADASS TITANIUM BLACKBIRD - Past bikes 1982 XS250 Yamaha & 1983 CB750F with 900 motor
    Ozblackbird.net Administrator

  12. #12
    Member 66's Avatar
    Join Date
    Dec 2008
    Location
    some where in the far east.
    Motorbike
    A fast one.
    Liked
    3461 times
    Posts
    12,562
    Post Thanks / Like
    Mentioned
    27 Post(s)
    Tagged
    0 Thread(s)
    Quote Originally Posted by forunna View Post
    i would rather be hit by a tonne of air than a tonne of water.
    Really?
    Even if one tonne came out of a garden hose over several hours and the other was the shockwave of an explosion?
    The greatest excitement comes from besting who you were yesterday.
    Likes henrys, GSXRossi liked this post

  13. #13
    Member Duffman's Avatar
    Join Date
    Nov 2004
    Location
    NOR
    Liked
    36 times
    Posts
    2,518
    Post Thanks / Like
    Mentioned
    2 Post(s)
    Tagged
    0 Thread(s)
    Have seen something similar. A 'water bridge' for fish to swim up and over a gap between 2 tanks. The lower pressure didn't bother the fish.
    Respect is earned, not enforced.

  14. #14
    Member Skut's Avatar
    Join Date
    Jun 2009
    Location
    Perth, Western Australia, Australia
    Motorbike
    RZ250
    Liked
    2138 times
    Posts
    10,669
    Post Thanks / Like
    Mentioned
    56 Post(s)
    Tagged
    0 Thread(s)
    Quote Originally Posted by Duffman View Post
    Have seen something similar. A 'water bridge' for fish to swim up and over a gap between 2 tanks. The lower pressure didn't bother the fish.


    It doesn't do squiddly difference to water pressure any more than the relative depth of the tank (ie if you were holding the weight of that tube by hand it would feel x grams heavy, but then if you increased the sides of the tanks to cover the tube i would be neutral buoyancy). Because the tanks are open everything is governed by ambient air pressure.

    edit: BTW this is how an old barometer works...
    Last edited by Skut; 12-01-2017 at 07:47 PM.

  15. #15
    Member Commander Keen's Avatar
    Join Date
    Jul 2008
    Location
    Perth
    Motorbike
    Gen 2 SV650
    Liked
    2501 times
    Posts
    10,006
    Post Thanks / Like
    Mentioned
    17 Post(s)
    Tagged
    0 Thread(s)
    Quote Originally Posted by forunna View Post
    there is no air .
    was just discussing with a mate.
    he wants to do something he has seen. an inverted fish tank in his pond so fish can swim up into it.
    he is worried the reversd pressure will crush a normal fish tank. i am not sure the fish will like it anyway.
    we couldnt decide what was pressure where. so we just ended up discussing it all in general.
    It would create negative pressure on any air left in the tank above the water level but the water pressure would stay the same.
    Fun thought. The air inside an inverted fish tank *under* water would increase in pressure due to the weight of water trying to compress it.
    Quote Originally Posted by Desmo View Post
    Why be a cunt about it?

  16. #16
    Member forunna's Avatar
    Join Date
    May 2014
    Location
    Darling Downs
    Motorbike
    Suzuki GN250
    Liked
    27 times
    Posts
    402
    Post Thanks / Like
    Mentioned
    0 Post(s)
    Tagged
    0 Thread(s)
    Quote Originally Posted by 66 View Post
    Really?
    Even if one tonne came out of a garden hose over several hours and the other was the shockwave of an explosion?
    ooo, nice scenario. I am familliar with 1 - 3 tonnes of water falling from a helicopter but not experienced a shockwave.
    anyway. that is getting off topic. naughty boy.

  17. #17
    Member forunna's Avatar
    Join Date
    May 2014
    Location
    Darling Downs
    Motorbike
    Suzuki GN250
    Liked
    27 times
    Posts
    402
    Post Thanks / Like
    Mentioned
    0 Post(s)
    Tagged
    0 Thread(s)
    Quote Originally Posted by Commander Keen View Post
    It would create negative pressure on any air left in the tank above the water level but the water pressure would stay the same.
    Fun thought. The air inside an inverted fish tank *under* water would increase in pressure due to the weight of water trying to compress it.
    so then how do you account for pressure increasing with depth if it the same pressure up the top?

    - - - Updated - - -

    Quote Originally Posted by Skut View Post


    It doesn't do squiddly difference to water pressure any more than the relative depth of the tank (ie if you were holding the weight of that tube by hand it would feel x grams heavy, but then if you increased the sides of the tanks to cover the tube i would be neutral buoyancy). Because the tanks are open everything is governed by ambient air pressure.
    thats cool.

  18. #18
    Member 66's Avatar
    Join Date
    Dec 2008
    Location
    some where in the far east.
    Motorbike
    A fast one.
    Liked
    3461 times
    Posts
    12,562
    Post Thanks / Like
    Mentioned
    27 Post(s)
    Tagged
    0 Thread(s)
    You quoted the answer mate.

    The water up top is at 'regular' pressure. It doesn't have any water other than itself squashing it.

    The water at the lowest points of the tank has all of the water above it 'squashing' it raising the pressure... by a bee's dick, no doubt.

    It doesn't 'fall' from the tube as it would need to push all of the water from the tanks upwards, which is resisted by the external air pressure acting on the surface.... I think.
    The greatest excitement comes from besting who you were yesterday.

  19. #19
    Member Joe Shabadoo's Avatar
    Join Date
    Aug 2009
    Location
    NoR
    Motorbike
    ZX10,CBR1000F
    Liked
    585 times
    Posts
    5,481
    Post Thanks / Like
    Mentioned
    8 Post(s)
    Tagged
    0 Thread(s)
    "air pressure" is caused by more molecules exerting force on a given area.. ie.. you compress it
    water is barely compressible, hence you increase water pressure by providing more of it over a certain area, or reducing the area
    ie. water cutting will direct the same amount of water as a slow running tap, onto a very small area

    under ocean is a function of gravity

    and wtf.. i agree with Skut
    better go murder a hippy and restore order to the universe

  20. #20
    Member Skut's Avatar
    Join Date
    Jun 2009
    Location
    Perth, Western Australia, Australia
    Motorbike
    RZ250
    Liked
    2138 times
    Posts
    10,669
    Post Thanks / Like
    Mentioned
    56 Post(s)
    Tagged
    0 Thread(s)
    Quote Originally Posted by Joe Shabadoo View Post

    and wtf.. i agree with Skut
    It happens sometimes. I feel equally dirty. I'm going to burn some incense and chant awhile

Bookmarks

Bookmarks

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •