Go Back   Physics Help Forum > High School and Pre-University Physics Help > Thermodynamics and Fluid Mechanics

Thermodynamics and Fluid Mechanics Thermodynamics and Fluid Mechanics Physics Help Forum

Reply
 
LinkBack Thread Tools Display Modes
Old Jun 23rd 2009, 02:39 PM   #1
Junior Member
 
Join Date: Jun 2009
Posts: 2
inverted wine bottle filled with water

Say you had a huge glass bottle 1 or 5 meters tall, and filled it up with pure water. A fully air inflated zip lock bag (but not so full that it starts to burst or change the plastic temperature) was then placed on top sealing off the bottle. The person then flipped the bottle upside down holding it in the air. The bag just hung there off the bottle in mid air. Say the zip lock bag is securely in place using good sealing glue around the bottle brim. i.e. the glue would be around the brim only and the water could still contact the soft bag surface. Air inside the bag has about 1atm pressure if gently filled up to maximum size. What would happen to the bag size, temperature, or even the water, when the bottle is inverted?

Gravity pulls water down causing hydrostatic pressure. However there is a 1atm plastic bag at the bottom stopping any downward flow of water! Air can't get in to the bottle because there is no way for it to enter. The glue stops the bag from ripping off the bottle and letting flow occur!

Would the plastic bag contract, expand, heat up, or have no change? Or a change in the water could occur such as ..?

I cannot put my finger on what would happen - and it is bugging me! The zip lock bag is not exposing direct air to the water - it is just exposing the plastic surface of the bag which touches air indirectly. The plastic flexible surface allows the water molecules' force to transmit through, since it is thin and soft enough.

It is similar to the surface tension in a straw that stops water from flowing down when you have your thumb on top of it. The bag acts as kind of a surface tension layer. However, this bag is filled up with air at 1atm, while the pressure in the water at the bottom should be 1atm *plus* hydrostatic pressure. There is an equilibrium problem if the bag stays the exact same and the water stays the same when the bottle is inverted. The molecules in the water should be high pressure, hitting the lower pressure plastic bag. High pressure tries to flow to low pressure zone (but water can't flow since the restrictive bag surface layer is there.. so methinks that the air in the bag might even heat up and/or expand to maintain equilibrium - but it cannot easily expand since it is already at its maximum bag size from when we previously inflated it fully! The static pressure of water could also decrease to lower than 1atm that it was originally trapped in the bottle at.)


??

Last edited by frend; Jun 23rd 2009 at 03:05 PM.
frend is offline   Reply With Quote
Old Jun 23rd 2009, 07:19 PM   #2
Senior Member
 
Join Date: Apr 2008
Location: HK
Posts: 886
Maybe the wine bottle is fully filled with pure water such that there is no air inside. In this case, the pressure inside the wine bottle is only the pressure due to weight of pure water which is weigh lower than atmospheric pressure. So there is always a net force preventing water from coming out due to pressure difference
werehk is offline   Reply With Quote
Old Jun 24th 2009, 09:37 AM   #3
Junior Member
 
Join Date: Jun 2009
Posts: 2
Originally Posted by werehk View Post
Maybe the wine bottle is fully filled with pure water such that there is no air inside. In this case, the pressure inside the wine bottle is only the pressure due to weight of pure water which is weigh lower than atmospheric pressure. So there is always a net force preventing water from coming out due to pressure difference
The water was never intended to come out in the first place so that is not the question at all. The bag is purposely glued to the bottle. The question is does the water affect the air molecules in the bag and influence them, or does the air influence the water, or does nothing happen at all, and why. I suppose the glue takes up all the stress and transfers the rest of the stress to the bottle that the glue is bonded to. If the bottle glass was drilled at the top end when it is inverted (so the bottom of the wine bottle), the question remains - would the air molecules in the bag be affected by the tremendous pressure of the water trying to come down into the bag, but can't, since the bag is glued tight to the brim. If there was a hole letting air in at one end of the bottle, and the water could "flow down" but then it was stopped by the bag surface, would this surface transmit pressure into the bag air.

I was thinking maybe the elastic plastic bag layer would be capable of transmitting some of the water pressure into the air bag, similar to how when one smashes a drum with a drum stick, the pressure of the drum skin transmits into the drum air and then pushes out air in the drum. If the drum was sealed shut this would resemble a plastic bag, and the air would compress or heat up if it could not expand or escape under pressure.

Last edited by frend; Jun 24th 2009 at 09:43 AM.
frend is offline   Reply With Quote
Reply

  Physics Help Forum > High School and Pre-University Physics Help > Thermodynamics and Fluid Mechanics

Tags
bottle, filled, inverted, water, wine



Thread Tools
Display Modes


Similar Physics Forum Discussions
Thread Thread Starter Forum Replies Last Post
Inverted pendulum roger Advanced Mechanics 2 Feb 21st 2013 11:59 AM
Dielectric Filled Parallel Plate Capacitor Question prodgod Electricity and Magnetism 0 Feb 25th 2011 09:44 AM
vibration on a bottle wujun Kinematics and Dynamics 4 Nov 14th 2009 06:26 AM
Object in fluid filled container sirdarksol Thermodynamics and Fluid Mechanics 1 Apr 27th 2009 10:10 PM
inverted nonlinear pendulum, show unstable. galactus Periodic and Circular Motion 0 Sep 26th 2008 03:28 PM


Facebook Twitter Google+ RSS Feed