Kirchoff's Laws restated

Thread Starter

Jerry-Hat-Trick

Joined Aug 31, 2022
201
1. When I drive into a roundabout but don't leave at one of the exits I'm going to upset other motorists
2. When I leave home to go for a walk by the time I'm home again I will have walked uphill and downhill in equal amounts

Can anyone explain why something so obvious should be named after our old friend Gustav?
 

MrChips

Joined Oct 2, 2009
27,641
Somewhere on the outskirts of Liverpool I went around a roundabout 5 times before I could make up my mind where I needed to go. The driver behind me following all around (as we were going together to the same place) thought that I was nuts.
 

WBahn

Joined Mar 31, 2012
27,853
1. When I drive into a roundabout but don't leave at one of the exits I'm going to upset other motorists
2. When I leave home to go for a walk by the time I'm home again I will have walked uphill and downhill in equal amounts

Can anyone explain why something so obvious should be named after our old friend Gustav?
1) Did they have roundabouts back then? ;)
2) Might not be so obvious if we had nonconservative gravitational fields such that it was possible to return to the point of origin while walking uphill the entire way.

Or maybe they did used to have those and that's how my dad was able to walk three miles to school each day, in the snow, uphill, both ways. :D
 

Ian0

Joined Aug 7, 2020
6,645
Somewhere on the outskirts of Liverpool I went around a roundabout 5 times before I could make up my mind where I needed to go. The driver behind me following all around (as we were going together to the same place) thought that I was nuts.
They have probably put traffic lights on it now, so that it would take all afternoon to drive around it five times.
 

Thread Starter

Jerry-Hat-Trick

Joined Aug 31, 2022
201
When I drive into a roundabout but don't leave at one of the exits I'm going to upset other motorists
I think that there is a capacitor analogy there somewhere. . .
That's a very good point - maybe it should change to " When I drive into a roundabout and just stop I'm going to upset other motorists"
 

MisterBill2

Joined Jan 23, 2018
13,680
Both of Kirchoffs laws allow circuits to be evaluated in a reasonable manner. I developed a similar theorum for an advanced complex numbers math class, which is that the sum of all "n" nth roots of an expression is zero. Unfortunately I was not able to develop an adequate derivation and proof and so I got no credit for it. But it always works, nobody ever came up with acomplex number expression that did not work. And how does the original staement relate to Kirchoff's laws???
 

Tonyr1084

Joined Sep 24, 2015
7,185
Kirchhoff's law says "What goes around comes around." In other words, all things are equal. If you do the calculations and you don't come back to where you started then you've done the calc's wrong. To me it's just a second way of looking at a circuit and evaluating whether I did it right or not. It's like casting out 9's.
Addition: checking by casting out 9's
Multiplication: checking by casting out 9's
Division: checking by casting out 9's
 

WBahn

Joined Mar 31, 2012
27,853
Back then? In Massachusetts, they’re still building new ones.
So? The question has nothing to do with whether they exist today or are still being built, the question is whether they existed at the time that Kirchhoff's Current Law was first formulated. My understanding is that KCL was formulated in ~1845 and that the first roundabouts were tested in ~1966. So it would be hard for ole Kirchhy to have seen the explanation of current in terms of roundabouts to be something so obvious.
 

WBahn

Joined Mar 31, 2012
27,853
Kirchhoff's law says "What goes around comes around." In other words, all things are equal. If you do the calculations and you don't come back to where you started then you've done the calc's wrong. To me it's just a second way of looking at a circuit and evaluating whether I did it right or not. It's like casting out 9's.
Addition: checking by casting out 9's
Multiplication: checking by casting out 9's
Division: checking by casting out 9's
As long as we keep in mind that Kirchhoff's Laws only work where they work. Each of them has an almost-never-stated assumption that is needed for them to work.
 

MisterBill2

Joined Jan 23, 2018
13,680
If the concept of computer driven cars is allowed to include weekly wireless updates, the whole thing is doomed . Every software update to fix a flaw will be a major safety recall,and who would want to ride in a car that was subject to major safety recalls every week??? So certainly the failure of the computer driven cars will be the failure of the software.
 

Ian0

Joined Aug 7, 2020
6,645
I can just imagine going out to the garage ready to set off to work and being met with a completely dead car showing “software update failed” on the display.
 

MisterBill2

Joined Jan 23, 2018
13,680
I can just imagine going out to the garage ready to set off to work and being met with a completely dead car showing “software update failed” on the display.
I had not considered that possibility, certainly another potential inconvenience.
The challenge of producing fully reliable code is that it is expensive, and takes about an hour per line to verify it. So how many millions of lines of code will one of these cars have in the driving system?? Certainly somebody can know what there is in the current vehicles, and tell us without giving away any secrets. How many lines of code are there in a windows OS?? that could provide a hint.
 

Ian0

Joined Aug 7, 2020
6,645
A successful software update could be even worse than a failed update.
”welcome to version 11.2”
and then you find that everything on the dashboard has been rearranged, it measures in kilometres instead of miles, and the pedal that used to make it go slower now speeds it up.
 
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