# \[Bulk\] Re: A chemical equation of equilibrium and negative feedback

**URL:** <http://discourse.iapct.org/t/bulk-re-a-chemical-equation-of-equilibrium-and-negative-feedback/12690>\
**Category:** CSG2006\
**Created:** [April 27, 2006, 9:12pm UTC](http://discourse.iapct.org/t/bulk-re-a-chemical-equation-of-equilibrium-and-negative-feedback/12690 "2006-04-27T21:12:08Z")\
**Posts on this page:** 2\
**Page:** 1

<div class="post-metadata">

**Author:** ![Martin\_Taylor2](http://discourse.iapct.org/letter_avatar_proxy/v4/letter/m/b4bc9f/32.png) [@Martin\_Taylor2](http://discourse.iapct.org/u/Martin_Taylor2)\
**Post date:** [April 27, 2006, 9:12pm UTC](http://discourse.iapct.org/t/bulk-re-a-chemical-equation-of-equilibrium-and-negative-feedback/12690/1 "2006-04-27T21:12:08Z")

</div>

[Bulk] Re: A chemical equation of equilibrium and  
negative  
[Martin Taylor 2006.04.27.17.03]

> [From Bjorn Simonsen (2006.04.27,21:35  
> EUST)]
> 
> I agree that the pendulum idea and the mass spring  
> idea can’t serve as models of purposeful behavior, but it looks to  
> me that the pendulum system is influenced by negative feedback after  
> the pendulum bob is released. I think upon the tension in the pendulum  
> suspension as the “perceptual signal” and a tension in the  
> pendulum suspension like the gravity force as the reference (this  
> happens when the pendulum hang still.

The  
difference between the restoration of the pendulum (or a spring, and  
the like) is that for them the energy required for the restoration is  
provided by whatever moved the item away from its equilibrium  
position. It’s just a conversion of the form of the energy to (jn the  
case of the pendulum) gravitational potential energy provided by  
whatever pushed the pendulum, and, on restoration, the dissipation of  
that energy into heat.

In a  
control system, whether it be physical or chemical or whatever, the  
energy required for restoration comes from a source independent of the  
energy suplied by the disturbnace. The control system’s  
“perception” extracts negligible energy from the disturbed  
system, but the output can supply as much energy as is available from  
its supply (conceivably up to the energy released by an  
H-bomb!).

Equilibrium systems do tend toward restoration of  
their central values, but they do so without outside energy sources  
(other than that supplied by whatever disturbed them away from the  
equilibrium in the first place).

Martin

---

<div class="post-metadata">

**Author:** ![Martin\_Taylor2](http://discourse.iapct.org/letter_avatar_proxy/v4/letter/m/b4bc9f/32.png) [@Martin\_Taylor2](http://discourse.iapct.org/u/Martin_Taylor2)\
**Post date:** [April 29, 2006, 5:21pm UTC](http://discourse.iapct.org/t/bulk-re-a-chemical-equation-of-equilibrium-and-negative-feedback/12690/2 "2006-04-29T17:21:58Z")

</div>

[Martin Taylor 2006.04.29.13.11]

> [From Rick Marken (2006.04.29.0840)]
> 
> > Bjorn Simonsen (2006.04.29,08:45 EUST)
> > 
> > I absolutely agree that \_if\_ the pendulum is a control system it is not a \_good\_ control system. There are many not good control systems. Is a thermostat a good control system? If you open the window in your living room a very cold winter day, it takes about the same time to create an equal and opposite force before the room temperature comes back to the set point temperature.
> 
> I think this misses the fact that pendulum barely controls at all while the thermostat, though not perfect, controls quite well. ...
> 
> So you can say that both the pendulum and thermostat are poor controllers but that the pendulum is worse. ...

I don't think you can say the pendulum is a controller of any kind, good or bad. It doesn't have any of the three main characteristics of a controller:

&nbsp;&nbsp;(1) the existence of a signal that represents the state of something outside itself,  
&nbsp;&nbsp;(2) use of a source of energy independent of whatever might disturb the state represented by the signal, and  
&nbsp;&nbsp;(3) an asymmetry between the force applied to the outer state to produce the signal and the force available to oppose changes in the outer state.

Whether a control system is "good" or "poor", it has all of those features. The pendulum has none.

I suppose you could say that Newton's law that a force is opposed by an equal an opposite reaction (e.g. a pendulum held at an angle) means that all mechanical effects involve negative feedback, but I'd call that stretching a point beyond the horizon! But even if you have an over-the-horizon radar, not all negative feedback systems are control systems.

Martin

PS. In a few minutes, I'm gone for a week or ten days, by which time this thread will probably be dead, so unless you disagree with the above in some arguable way, I don't expect to contribute to it further.