What Are Critical, Over, and Under Damping in Electrical Circuits?

[Hoofbeat]

Could someone please give me a QUALITATIVE description of:

-critical damping
-over damping
-under damping

So I can understand the physics behind the oscillatios in a circuit. I know the mathematical explanations (ie. over damping is when the characteristic polynomial solutions are both negative real numbers etc).

Thanks

 

[HallsofIvy]

It might be clearer to think of this in terms of a "shock absorber" system in a car: a spring with a damping force.

"under damped" means you - bounce, bounce, bounce with each bounce less than the one before. If you graph the motion (or the current in a circuit) you see a succession of peaks and valleys with the height between peak and valley getting smaller. If you put an ammeter into an "under damped" circuit, you see the needle swinging back and forth between positive and negative- a little less on each side with each swing, until it settles at 0.

"over damped" is no bouncing at all. There is a smooth return from the height to 0. If you graph that, you see a smooth curve dropping to 0 but not going below 0. If you put an ammeter in an over damped circuit, you see the needle swinging steadily down to 0.

"critically damped" looks exactly like "over damping"- there is no swing below and then back above 0. The only difference between "over damped" and "critically damped" is that if you reduce the damping at all, you get "under damped".

 

[Hoofbeat]

ok thanks that really helps. So is basically critical damping sort of mid-way between under damped and over damped in the sense that it provides just enough damping to reduce most of the amplitude of oscillation, but the oscillation still actually continues?