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Today's Topics:
1. Volume non-conservation example (Thomas Regan)
2. Re: Volume non-conservation example (Scott Goelzer)
3. Re: Volume non-conservation example (Joseph Bellina)
---------- Forwarded message ----------
From: Thomas Regan <tregan@alumni.stanford.edu>
To: phys-l@mail.phys-l.org
Cc:
Bcc:
Date: Sat, 10 May 2025 18:49:35 -0400
Subject: [Phys-L] Volume non-conservation example
I’m looking for a demonstration that volume is not a conserved quantity.
Here’s what I have come up with.
Mark the height of water in an open-topped container. Define the system to
be the volume occupied by the liquid water, the container up to the mark.
Put the container in the freezer. Upon freezing, the water/ice expands
upwards past the mark. There has been a (non-zero) flow of water/ice volume
out of the system, upward past the mark. However, the system, the container
up to the mark, is still full of ice. The change in water/ice volume in the
system is zero. The flow does not equal the change so volume is not a
conserved quantity.
This can be run in reverse as well. Start with ice, and mark the height of
the ice. The container up to the mark is our system. Put the container
somewhere at room temperature. The ice melts, and the level of the
water/ice falls below the original mark. There is now empty space in the
system. The volume of water/ice in the system has changed. However, there
has been no flow of water/ice volume out of the system, so the flow is
zero. Once again, the flow does not equal the change so volume is not a
conserved quantity.
What do you think? Is this a legitimate demonstration of non-conservation?
---------- Forwarded message ----------
From: Scott Goelzer <s.goelzer@comcast.net>
To: Phys-L@phys-l.org
Cc:
Bcc:
Date: Sat, 10 May 2025 19:54:53 -0400
Subject: Re: [Phys-L] Volume non-conservation example
The classic from chemistry is 50 ml of ethanol and 50ml of water poured
into a grad cylinder. Produces ~90ml of mixture.
Scott
On May 10, 2025, at 6:49 PM, Thomas Regan via Phys-l <phys-l@mail.phys-l.org> wrote:
to
I’m looking for a demonstration that volume is not a conserved quantity.
Here’s what I have come up with.
Mark the height of water in an open-topped container. Define the system
be the volume occupied by the liquid water, the container up to the mark.volume
Put the container in the freezer. Upon freezing, the water/ice expands
upwards past the mark. There has been a (non-zero) flow of water/ice
out of the system, upward past the mark. However, the system, thecontainer
up to the mark, is still full of ice. The change in water/ice volume inthe
system is zero. The flow does not equal the change so volume is not aof
conserved quantity.
This can be run in reverse as well. Start with ice, and mark the height
the ice. The container up to the mark is our system. Put the containernon-conservation?
somewhere at room temperature. The ice melts, and the level of the
water/ice falls below the original mark. There is now empty space in the
system. The volume of water/ice in the system has changed. However, there
has been no flow of water/ice volume out of the system, so the flow is
zero. Once again, the flow does not equal the change so volume is not a
conserved quantity.
What do you think? Is this a legitimate demonstration of
_______________________________________________
Forum for Physics Educators
Phys-l@mail.phys-l.org
https://www.phys-l.org/mailman/listinfo/phys-l
---------- Forwarded message ----------
From: Joseph Bellina <inquirybellina@comcast.net>
To: Phys-L@phys-l.org
Cc:
Bcc:
Date: Sat, 10 May 2025 19:55:35 -0400
Subject: Re: [Phys-L] Volume non-conservation example
How about observing a thermometer?
Sent from my iPhone
On May 10, 2025, at 6:49 PM, Thomas Regan via Phys-l <phys-l@mail.phys-l.org> wrote:
to
I’m looking for a demonstration that volume is not a conserved quantity.
Here’s what I have come up with.
Mark the height of water in an open-topped container. Define the system
be the volume occupied by the liquid water, the container up to the mark.volume
Put the container in the freezer. Upon freezing, the water/ice expands
upwards past the mark. There has been a (non-zero) flow of water/ice
out of the system, upward past the mark. However, the system, thecontainer
up to the mark, is still full of ice. The change in water/ice volume inthe
system is zero. The flow does not equal the change so volume is not aof
conserved quantity.
This can be run in reverse as well. Start with ice, and mark the height
the ice. The container up to the mark is our system. Put the containernon-conservation?
somewhere at room temperature. The ice melts, and the level of the
water/ice falls below the original mark. There is now empty space in the
system. The volume of water/ice in the system has changed. However, there
has been no flow of water/ice volume out of the system, so the flow is
zero. Once again, the flow does not equal the change so volume is not a
conserved quantity.
What do you think? Is this a legitimate demonstration of
_______________________________________________
Forum for Physics Educators
Phys-l@mail.phys-l.org
https://www.phys-l.org/mailman/listinfo/phys-l
_______________________________________________
Forum for Physics Educators
Phys-l@mail.phys-l.org
https://www.phys-l.org/mailman/listinfo/phys-l