Isn't that what I quoted from Wiki?
Indeed! Because I was in honors EE I was required to take the freshman and sophomore ME major courses as electives. I found them quite enjoyable.
...Jim Thompson
Knock off the childishness You just can't resist trying to start a pissing contest can you? ...Jim Thompson
Staying on topic is the opposite of a pissing contest.
Viscoscity is the analog of resistance.
Volts : amps for a resistor
Speed : force for viscous drag
In both cases, there is a square law relation between the forcing function (volts, speed) and power.
Sliding friction is analogous to constant current. The relationship between input and power is linear.
core losses got me thinking about other types of damping. And I was wonder ing if there is an electrical equivalent of friction? It seems to me that i t could be a constant voltage loss. So maybe just some diodes in an LC circ uit? If you think of resistance as viscoscity Current in a resistor is prop ortional to voltage Force in a viscous coupling is proportional to velocity (the classic machanical analog of an RLC uses a dashpot for the resistior) then the analog of friction is a constant current. A practical constant-cu rrent resistor is a pair of depletion fets back-to-back. Above a volt or tw o, anyhow. If you put one of these across your resonant tank, you'd get the Christmas-tree (linear) amplitude decay like you see with the diodes... no t exponential decay. I think. Supertex has LT Spice models of their depleti on fets.
that
ld be
OK. (oops I drew a ring diode first.) How the bleep does current get thro ugh the bridge. Or is that what the current source is for. I drew this,
Sig in/ out. | .--|>|--+--|>|--. | | gnd-+ +-->current sink | | .--|>|--+--|>|--. | Sig in/out
I don't think that's going to work though.
Not to worry I'll play with it over the weekend. This is only 'for fun'.
George H.
Spelled 'Viscosity'.
On Fri, 12 Jul 2013 13:37:50 -0700 (PDT), George Herold wrote:
The current source has to float.
Try this. Note that the ringing decay is linear, not exponential. This is friction, not viscosity like a regular resistor. It's a cool concept; thanks for introducing it.
There must be deep physical issues here. Does a fristor have Johnson noise? Its unit of measurement is amperes, not ohms.
Version 4 SHEET 1 880 680 WIRE -224 32 -432 32 WIRE -80 32 -224 32 WIRE 208 32 -80 32 WIRE 80 128 32 128 WIRE 208 128 208 32 WIRE 208 128 144 128 WIRE 256 128 208 128 WIRE 368 128 320 128 WIRE -432 160 -432 32 WIRE -224 160 -224 32 WIRE -80 160 -80 32 WIRE 32 192 32 128 WIRE 160 192 32 192 WIRE 368 192 368 128 WIRE 368 192 240 192 WIRE 32 272 32 192 WIRE 80 272 32 272 WIRE 208 272 144 272 WIRE 256 272 208 272 WIRE 368 272 368 192 WIRE 368 272 320 272 WIRE -432 368 -432 240 WIRE -224 368 -224 224 WIRE -224 368 -432 368 WIRE -80 368 -80 240 WIRE -80 368 -224 368 WIRE 208 368 208 272 WIRE 208 368 -80 368 WIRE -80 400 -80 368 FLAG -80 400 0 SYMBOL diode 80 144 R270 WINDOW 0 40 7 VTop 2 WINDOW 3 69 45 VBottom 2 SYMATTR InstName D1 SYMATTR Value Di SYMBOL diode 256 144 R270 WINDOW 0 44 17 VTop 2 WINDOW 3 72 53 VBottom 2 SYMATTR InstName D2 SYMATTR Value Di SYMBOL diode 80 288 R270 WINDOW 0 -33 18 VTop 2 WINDOW 3 -6 58 VBottom 2 SYMATTR InstName D3 SYMATTR Value Di SYMBOL diode 256 288 R270 WINDOW 0 -33 21 VTop 2 WINDOW 3 -6 60 VBottom 2 SYMATTR InstName D4 SYMATTR Value Di SYMBOL current 240 192 R90 WINDOW 0 39 92 VBottom 2 WINDOW 3 11 -13 VTop 2 SYMATTR InstName I1 SYMATTR Value 5m SYMBOL ind -64 256 R180 WINDOW 0 49 82 Left 2 WINDOW 3 47 41 Left 2 SYMATTR InstName L1 SYMATTR Value 1m SYMBOL cap -240 160 R0 WINDOW 0 -54 14 Left 2 WINDOW 3 -57 54 Left 2 SYMATTR InstName C1 SYMATTR Value 1µ SYMBOL current -432 240 R180 WINDOW 0 21 -17 Left 2 WINDOW 3 -174 -162 Left 2 WINDOW 123 0 0 Left 2 WINDOW 39 0 0 Left 2 SYMATTR InstName I2 SYMATTR Value PULSE(0 1 0 0 0 10u) TEXT 88 400 Left 2 !.model Di D(Vfwd=0) TEXT -216 -32 Left 2 !.tran 10m TEXT 112 -16 Left 2 ;Frictional equivalent resistor TEXT 240 32 Left 2 ;JL July 12, 2013
Did more than one of us sleep through physics class?
The kind of viscous friction that you describe (for lack of a better term) is virtually unheard of in the real world. In the real world, one always sees Colombic friction (Wikipedia's "kinetic" friction) and nearly always stiction.
While one can argue that the Wikipudlians don't always get things right, this article is certainly in line with my experience making motors and other motion control systems behave correctly, and with various articles that I have read, both by control wonks and by tribologists.
When I went through physics in the early 60's, they did not call it stiction. It was called static coefficient of friction as opposed to dynamic coefficient of friction.
like a diode (or two antiparallel) in series with the inductor
like a sidac in series
yeah, it can be used that way too.
now I'm trying to figure out how to model Newton's Cradle as an electrical system, I guess I start with some coupled inductors....
that's not ideal friction.
friction is the ration between the contact force and the drag force it is not dependant on motion, and often greater than small forces.
Ahh, ok I was wondering if I could float a current source? ... No don't tell me.. I must be able to make something out of opamps.
(I'll check out your spice file later.)
Ahh.. well Vald started it with core losses. Friction seems weird though... it's got a 'scale' the size of the loss, where as resistance is linear, ..all the way down... (I'm trying to channel Terry Pratchet, "Elephants all the way down...")
Seems like some analog computer guy must have done friction long ago.
I don't have any use for this idea. But that's ok. Maybe I'll understand regular friction better. I guess you could damp a resonance against small signals, but still ring for a while on big stuff.
George H.
So (I think) I'm talking about an electrical analog of dynamic friction. Though the spice file I posted looks much more like static friction, big step changes where the current goes to zero. Maybe they are not all that different in terms of energy loss. (For a resonant circuit.)
George H.
Hopeless.
If you're treating current as velocity and voltage as force, then dynamic friction would be simulated by back to back zener diodes.
Stiction would be something like a diac.
Core losses are due to hysteresis. The medium is being force aligned and flipped and there is a friction between those forced transitions.
In an electrical current and the medium it flows through, the friction is in the exchange from atom to atom. and those atoms may be in a matrix (chemical compound?) of less conductive components, so we calibrate electron flows and heating and the management of said heat to arrive at "components" which can operate at a given stated value under a given stress level without straying so far from the stated value that it no longer qualifies as the component it was declared as. This is why there are different wattage resistors and designers use that type which applies to their application.
I'm sure we're all grateful for the physics lesson, but I'm also pretty sure the OP wasn't asking about resistance.
Sylvia.
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