Releasing stored energy

[Shannen Durphey]

Joe Boucher wrote:

> Thsi is one wild discussion.
>
> At 06:38 PM 3/10/98 -0700, you wrote:
> >
> >
> >Lino Verna wrote:
> >
> >> When you push on a wall with 200lb's of force it
> >> >> pushes back with the same amount and yet it did not
> >> >> move,,,hmmmmmm,,,,but it is stored energy
> >>
> >> >
> >> >If you push on the wall and it pushes back, but nothing moves, you've
> >> >created heat!  Energy dissipates into the air.
> >>
> >> >Wouldn't stored load be called inertia?  I seem to remember doing some
> >> >inertia equations in a physics class.  Can't remember the equations but I
> >> >sure remember doing them.
>
> Inertia is resitance to change in movement and is a property of mass.  More
> mass, more resistance.  Stored energy is potential energy, for example, a
> compressed spring (or wall) or water about to flow down a tube and through
> a turbine to make electricity.
>
> >> Actually the wall does move, and that is how it stores the energy.
> >> Push on anything and it will move.
> >>
> >> Tell you what, put on that cone shaped hat like the rest of us wear and
> >> jump.
> >> I guarantee that the earth will move the other way as a reaction to your
> >> jump.
> >> That is, only if you're wearing that hat though...
> >>
> >> lino
> >
> >  Ahhh!  But the measure of anything depends on a reference point.  With
> Earth
> >as a reference point, only I and my cone shaped hat will move.  When I land,
> >the Earth is not moving, and much too quickly I am not either.  But I sure
> >have expended my energy and likely cannot find any of it stored up in the
> >place where I hit.
> >
> >Believe me about this.  I have a subscription to the cone shaped hat of the
> >month club.
> >
> >Ok, I'll probably get flamed for this, but there are circumstances where
> >pushing can't cause movement.  There is simply not enough force in the push.
> >Maybe where I'm getting confused is my idea about "stored" energy.  It seems
> >that if energy were being stored in the wall, it would be accessible.  Like a
> >flywheel spinning on a shaft has stored energy.
>
> In practical terms you're correct.  But in reality if you push on something
> there is movement.  You might have to get down to the point of watching the
> atoms at the area of the push to see the movement, but it's there.
>
> >But how can you measure the energy "stored" in the wall?  Some of you ME
> types
> >can surely help me here.
>
> Potential energy stored in a spring is 1/2 times the spring coefficient
> times the square of the compression distance.  Tell me the spring
> coefficient of the wall and we'll figure it out.  Can we convert the stored
> energy into real work.  No.
>
> >It seems that there is certainly a definition of
> >pushing without movement.  It's called Force.
> >And pushing with movement is Work.  ('course pushing without movement can
> be a
> >lot of work, too).  So the energy must go somewhere.  In many cases it's
> heat.
> >But what about gravity and the telephone supported by my computer table......
> >If I balance this glass of water like so... ah, but, um,,,
> >
> >Uh-oh.  My wheels are spinning again.
> >
> >Time to go re-arrange the hat collection.
> >
> >Shannen
>
> I sure miss the dormitory bullshit sessions.
> Joe Boucher
> '70 RS/SS Camaro  '81 TBI Suburban

  Oh man.  Another problem which could have been avoided by developing math as the
first spoken language.  Much easier to understand now.

Ok.  If Ep of wall=1/2 times the spring coefficient times the square of the
compression distance, the only reason no practical work can be done is because the
movement of the wall is so small.  However, as far as energy being stored in the
wall, with regards to a simple linear motion opposite in direction to a
hypothetical push, it isn't there.  Potential energy requires an energy source
present in order to exist.  In the case of the wall, it's the pusher.

But inertia is different.  Yes inertia is a function of mass, but isn't it also
directly related to velocity?  And velocity is speed+direction.  Inertia is real.
It can be seen, can be experienced.  It's part of our instinctual understanding of
the universe.  We don't kneed to know physics to realize that a baseball driven
straight at us off a hard pitch isn't going to stop very easily..  The inertia of
an object can be considered an energy source. A falling body has energy.  It
strikes an object, and it gives up this energy.  A spinning tire has energy. Hook
it to asphalt, and it gives up this energy.

I'm going to say that potential energy doesn't actually exist at all.  It's only a
stage between changes in inertia.  Or better yet, a description of a state of
change in inertia.  Potential energy isn't real in the sense that it can be
measured.  It's only reason for being is to describe what's happening between
measurable events.  We know the height of a certain block from the ground and it's
mass.  We know that after the block is dropped x distance it will have reached a
measurable speed (is it [x][rate of acceleration due to gravity]) and can exert a
force based on it's inertia at the time. (I'm not trying to be vague, I just can't
remember the needed formulas here.) Since it takes energy to exert force, we say
that the block must have had potential energy, and we can predict how much it will
have in a similar situation.  But we can never measure it directly.

I should really go back to school.

Shannen