| Topic: |
Science > Physics |
| User: |
"Jaga" |
| Date: |
03 Jun 2007 10:42:30 PM |
| Object: |
What happened to energy conservation? |
Every child at school is taught that the total energy is always
conserved. Yes, the entropy may increase, lots of useful energy can be
converted to the heat but still, the total energy is always the same.
If this is true how energy is conserved in a following situation:
there is a string and this string was squizzed- lots of work was done
to keep it together. We pour this string to the strong acid and then
it dissolves completely. What did happen to the accumulated potential
energy there? Does it really make so much difference whether the
string is squizzed, pulled or just let free?
Jaga
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| User: "Sam Wormley" |
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| Title: Re: What happened to energy conservation? |
03 Jun 2007 11:07:50 PM |
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Jaga wrote:
Every child at school is taught that the total energy is always
conserved. Yes, the entropy may increase, lots of useful energy can be
converted to the heat but still, the total energy is always the same.
If this is true how energy is conserved in a following situation:
there is a string and this string was squizzed- lots of work was done
to keep it together. We pour this string to the strong acid and then
it dissolves completely. What did happen to the accumulated potential
energy there? Does it really make so much difference whether the
string is squizzed, pulled or just let free?
Jaga
The total energy of the system is conserved.
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| User: "PD" |
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| Title: Re: What happened to energy conservation? |
04 Jun 2007 12:36:04 PM |
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On Jun 3, 10:42 pm, Jaga <jagodakla...@gmail.com> wrote:
Every child at school is taught that the total energy is always
conserved. Yes, the entropy may increase, lots of useful energy can be
converted to the heat but still, the total energy is always the same.
If this is true how energy is conserved in a following situation:
there is a string and this string was squizzed- lots of work was done
to keep it together. We pour this string to the strong acid and then
it dissolves completely. What did happen to the accumulated potential
energy there? Does it really make so much difference whether the
string is squizzed, pulled or just let free?
Jaga
There are likely two things that happen to that stored potential
energy. One is that when the acid breaks a molecular bond in the
string, the stored potential energy is added to the heat released in
the chemical reaction. Secondly, when most of the string is eaten away
and the string breaks while still under tension, the stored potential
energy goes into the kinetic energy of the flying ends of the snapped
string. This is why when a steel cable on a bridge breaks, the flying
cable can cut a car in half.
PD
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| User: "Mitchell Jones" |
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| Title: Re: What happened to energy conservation? |
17 Jun 2007 11:21:58 PM |
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In article <1180978564.317351.197110@k79g2000hse.googlegroups.com>,
PD <TheDraperFamily@gmail.com> wrote:
On Jun 3, 10:42 pm, Jaga <jagodakla...@gmail.com> wrote:
Every child at school is taught that the total energy is always
conserved. Yes, the entropy may increase, lots of useful energy can be
converted to the heat but still, the total energy is always the same.
If this is true how energy is conserved in a following situation:
there is a string and this string was squizzed- lots of work was done
to keep it together. We pour this string to the strong acid and then
it dissolves completely. What did happen to the accumulated potential
energy there? Does it really make so much difference whether the
string is squizzed, pulled or just let free?
Jaga
There are likely two things that happen to that stored potential
energy. One is that when the acid breaks a molecular bond in the
string, the stored potential energy is added to the heat released in
the chemical reaction. Secondly, when most of the string is eaten away
and the string breaks while still under tension, the stored potential
energy goes into the kinetic energy of the flying ends of the snapped
string. This is why when a steel cable on a bridge breaks, the flying
cable can cut a car in half.
PD
***{Yes, and while energy stored in a piece of string would likely have
a negligible effect on the temperature of the acid that dissolved it,
experiments have been done in which large springs were compressed,
clamped in the compressed state, and dissolved in acid. Result: the
temperature of the liquid changed in an amount that reflected the energy
released by the chemical reaction, plus the energy stored in the
compressed spring. --MJ}***
*****************************************************************
If I seem to be ignoring you, consider the possibility
that you are in my killfile. --MJ
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| User: "Jaga" |
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| Title: Re: What happened to energy conservation? |
10 Jun 2007 12:29:00 AM |
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On Jun 4, 11:36 am, PD <TheDraperFam...@gmail.com> wrote:
On Jun 3, 10:42 pm, Jaga <jagodakla...@gmail.com> wrote:
Every child at school is taught that the total energy is always
conserved. Yes, the entropy may increase, lots of useful energy can be
converted to the heat but still, the total energy is always the same.
If this is true how energy is conserved in a following situation:
there is a string and this string was squizzed- lots of work was done
to keep it together. We pour this string to the strong acid and then
it dissolves completely. What did happen to the accumulated potential
energy there? Does it really make so much difference whether the
string is squizzed, pulled or just let free?
Jaga
There are likely two things that happen to that stored potential
energy. One is that when the acid breaks a molecular bond in the
string, the stored potential energy is added to the heat released in
the chemical reaction. Secondly, when most of the string is eaten away
and the string breaks while still under tension, the stored potential
energy goes into the kinetic energy of the flying ends of the snapped
string. This is why when a steel cable on a bridge breaks, the flying
cable can cut a car in half.
PD
that is a very interesting analysis thanks. When I thought about it
later I figured out that these things are difficult to compare since
it is like comparison of the forces in macroworld with the molecular
level forces during chemical reaction. Besides, the amount of the
potential energy which was delivered is probably very small compared
to the heat of reaction
interesting example with the steel cable!
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