On 13 Mar 2011 at 15:31, Victoria Hughes wrote: > Well, I know this is another one of my out-of-left-field questions, > but out of curiousity is gravity a constraint or a force?
On Newton's account of things (if not in his language?) it's a force; I think also in Special Relativity. In General Relativity, I think I ought to say it's a constraint, but I don't know what Real Physicists say. Some witty physicist (John Archibald Wheeler, if Google can be trusted) put it nicely as "Matter tells space how to curve, and space tells matter how to move." Force being, more or less by definition, what "tells matter how to move" (more precisely and correctly: how to *change* how it is moving), here we see gravity in its avatar as the shape of space: which sure seems to me like it should be called a constraint. I have no idea what the Einstein's "gravitational constant" (that the cosmologists claim is not actually, you know, *constant*) means for this style of explanation. > Does it > depend on where you measure it? What about at planetary distances? > Really I am just curious and not attempting to poke or provoke. > Thank you- > Victoria > > > [ ps so is my ignorance a constraint or a force, and what changes that? > > > On Mar 13, 2011, at 9:45 AM, Russ Abbott wrote: > > > Eric and Lee have nice discussions. The only thing I would add as > > something of a generalization is that constraints have to do with > > the structure of something--in Lee's case, the way the hand is > > structured and how it's held together at the joints and in Eric's > > case the structure created by the bumpers on the alley. Forces > > become important when one discusses the expenditure of energy--in > > Lee's case the use of energy to move the hand given the constraints > > and in Eric's case the energy that imparted momentum to the ball. > > > > One thing that makes this more difficult is that many social (and > > biological) systems expend energy to maintain structure: a police > > force is an example as is a government more generally. In Lee's and > > Eric's examples, we imagine the structures being maintained > > statically (and indefinitely) by whatever holds the pieces in place. > > In social and biological organizations many of the structures would > > fall apart were it not for the continual expenditure of energy. > > > > -- Russ Abbott > > _____________________________________________ > > Professor, Computer Science > > California State University, Los Angeles > > > > Google voice: 747-999-5105 > > blog: http://russabbott.blogspot.com/ > > vita: http://sites.google.com/site/russabbott/ > > _____________________________________________ > > > > > > > > On Sun, Mar 13, 2011 at 7:57 AM, ERIC P. CHARLES <e...@psu.edu> wrote: > > I suspect that outside the context of a specific example, this is > > not really possible to answer. Throwing your own pet distinction > > back at you, we need to know what we are trying to explain, so we > > can avoid slipping levels of analysis. I have not read the author in > > question, but suspect an example (with slippage) would go something > > like this: > > > > Imagine a child bowling with bumpers. The child causes the ball to > > roll down the lane, and to hit the pins. The bumpers constrain the > > path of the ball to be in the direction of the pins. That is, the > > overall path of the ball is roughly: /\/\/\/\/\/\/\/\X (our lucky > > kid rolls a strike), and when asked to explain that macro-movement - > > the child causes, the bumpers constrain. If that is correct, it is > > going to be a big problem if we slip our level of analysis to the > > details of the path of the ball. If, instead of explaining the > > overall pattern, we ask about a single jag (a single \) then the > > bumper has a causal roll, in that it applied force to the ball (or > > redirected force applied to it by the ball). So, what we find from > > our example is that all "constraints" are "causes" at another level > > of analysis - which would be terribly confusing if not specified. > > > > For a more flippant example: Does my cable TV subscription constrain > > what I watch, or cause it? When I am flipping through the channels, > > it constrains it. When I stay on the same channel, whatever is on, > > it causes it. > > > > Another thought: This is the same silly distinction made by people > > who are not willing to commit fully to epigenetic development. They > > say things like "genes create the constrains that the environment > > works within." (The most obvious reason it is silly is because one > > could just as easily reverse the terms.) > > > > Hope something in that helps, > > > > Eric > > > > > > On Sun, Mar 13, 2011 01:45 AM, "Nicholas Thompson" > > <nickthomp...@earthlink.net > > > wrote: > > Dear anybody, > > > > > > > > > > > > > > I am reviewing a book by a psychologist in which the author makes a > > distinction between constraints and causes. Now perhaps I am over > > thinking this, but this distinction seems to parallel one made by > > Feynman in his famous physics text, where he defines a constraint as > > a force that does no work. If I have it right, the idea goes like > > this: If you place a bowling ball on a table the ball neither > > receives work from gravity nor does the table do any work holding > > the ball up because the ball does not move, and work is just the > > movement of mass. Indeed, even if you were to slide the table out > > and, with great effort, were to hold the ball in the same position > > for an hour, you wouldn´t be doing any work, either. Similarly, in > > a ball rolling down an inclined plane, the plane itself does no work > > because even tho it affects the motion of the ball, its effect is > > always perpendicular to the motion of the ball and there fore > > affects its motion neither one way or the either .... i.e., does no > > work! > > > > > > > > > > > > > > Now I would leave it at that except that Alicia Juarrero in her book > > also makes a huge distinction between forces and constraints, one > > which I think our own Steve Guerin applauds. It is the constraints > > that make it possible for far-from-equilibrium systems to self > > organize and do work. Perhaps I can make this work with Feynman´s > > definition if I think about the dam beside a water wheel, and the > > water wheel itself, as applying constraints to the water (they do no > > work themselves) which make it possible for the falling water to do > > work. Am I still on track, here? > > > > > > > > > > > > > > Now Juarrero goes on to make a distinction between between context > > sensitive and context-free. I have read these passages dozens of > > times and I just don´t understand this distinction. Can anybody out > > there explain it to me as to a Very Small Child. > > > > > > > > > > > > > > Thanks, > > > > > > > > > > > > > > Nick > > > > > > > > > > > > > > > > > > > > > > > > > > Nicholas S. Thompson > > > > > > > > Emeritus Professor of Psychology and Biology > > > > > > > > Clark University > > > > > > > > http://home.earthlink.net/~nickthompson/naturaldesigns/ > > > > > > > > http://www.cusf.org > > > > > > > > > > > > > > > > > > > > ============================================================ > > > > FRIAM Applied Complexity Group listserv > > Meets Fridays 9a-11:30 at cafe at St. John's College > > lectures, archives, unsubscribe, maps at http://www.friam.org > > > > > > Eric Charles > > > > Professional Student and > > Assistant Professor of Psychology > > Penn State University > > Altoona, PA 16601 > > > > > > > > ============================================================ > > FRIAM Applied Complexity Group listserv > > Meets Fridays 9a-11:30 at cafe at St. John's College > > lectures, archives, unsubscribe, maps at http://www.friam.org > > > > ============================================================ > > FRIAM Applied Complexity Group listserv > > Meets Fridays 9a-11:30 at cafe at St. John's College > > lectures, archives, unsubscribe, maps at http://www.friam.org > > ============================================================ FRIAM Applied Complexity Group listserv Meets Fridays 9a-11:30 at cafe at St. John's College lectures, archives, unsubscribe, maps at http://www.friam.org
