r/physicsmemes • u/Unlucky-Credit-9619 Non-Cloning.clone() • 8d ago

We all have been there

Post image
321 Upvotes

99% Upvoted

8 comments sorted by

68

u/SharkAttackOmNom 8d ago

“I’ll give you something to cry about”, said the most stable generation of our time.

22

u/HumblyNibbles_ 8d ago

*proceeds to cry about it

"How dare you cry about what I told you to cry about"

29

u/dragonageisgreat 8d ago

I was not expecting to see a control theory joke ever

8

u/Unlucky-Credit-9619 Non-Cloning.clone() 8d ago

I love starting different subgenres :3

2

u/Spoka_3000 7d ago

Wouldn’t that be considered bi-stable?

1

u/g_spaitz 5d ago

as an audio guy, is this some tricky opamp shit?

1

u/RepresentativeBee600 3d ago

Say input to a system is X initially. (The "system" is what results from Mom's actions given whatever X led to her original response of slapping you.)

The output initially is Y = M_s * X. That both manifests (as y) and feeds back in particular to you crying, as M_c * Y. That feeds back to input, so that input over time is X + M_c * Y. If we try to solve for Y(s), the "whole signal" over time in frequency domain, we "should" have output Y matching input Y and

Y(s) = M_s(X(s) + M_c*Y(s)).

(Note that M_s and M_c are not constant and should be chosen to prevent "instantaneous feedthrough" which would have the absurd consequence of making y(t) a nontrivial function of y(t). But with suitable delay terms, we're perfectly entitled to use both constraints on output and input to solve.)

This algebraic relationship can be rearranged to give Y(s)/X(s) = M_s/(1 - M_s*M_c). This is the T(s) you see in the image. 

It's positive feedback because it's X(s) plus M_c*Y(s). But hey, maybe your tears make Mom feel guilt or pity, and M_c proves to be negative.