# Dampening in a circuit

kickthatbike
This is more of a conceptual question.Would overdampening in a circuit (from a resistor) be analogous to stretching a spring past critical distances in a mass-spring system? Or perhaps swinging a pendulum from excessively large angles?

This is more of a conceptual question.Would overdampening in a circuit (from a resistor) be analogous to stretching a spring past critical distances in a mass-spring system? Or perhaps swinging a pendulum from excessively large angles?

No, not really. Damping (not dampening) refers to the amount of energy lost relative to the amount of energy stored. Overdamping in an electrical circuit is more analogous to a pendulum swinging while submerged in honey. If you pull back the pendulum and release it, it will slowly fall back to its lowest position without oscillating, because the friction with the honey dissipates energy and limits how fast the pendulum can move.

kickthatbike
So something like air friction while falling?

Homework Helper
Gold Member
So something like air friction while falling?

That's closer. In fact, if air friction is assumed proportional to speed, then it's an exact analog.

But, 'overdampening' refers to an oscillatory system. So if you had a mass on a spring, with air dampening the motion, then the diff. eq. would be the same as if the mass were dampened by a dashpot or similar device. And there would be a minimum dampening constant of air friction that resulted in an overdampened system.

So something like air friction while falling?

Right. But a pendulum in air would be considered damped, but not overdamped. So it would oscillate back and forth, with the amplitude of each swing getting smaller and smaller. This would be considered underdamped. An overdamped pendulum is when the friction is so large that it doesn't oscillate at all, but slowly swings back to it's equilibrium position. There is another possibility, called critically damped, in which the damping is just right so that the pendulum settles into its equilibrium position as quickly as possible.

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kickthatbike
So if I understand this right, an overdamped circuit would discharge it's capacitor, and then settle down to have no current, as opposed to the capacitor and inductor working to keep a steady current? And all of this would be caused by a high amount of resistance (literal resistance, from a resistor)?

Homework Helper
Gold Member
So if I understand this right, an overdamped circuit would discharge it's capacitor, and then settle down to have no current, as opposed to the capacitor and inductor working to keep a steady current? And all of this would be caused by a high amount of resistance (literal resistance, from a resistor)?

The current would exponentially approach zero without reversing direction if damping is critical or higher.

If there is even a small reversal of current, you'd have underdamping.

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kickthatbike
Very rad. Thanks to both of you.