Rule of thumb · PhysicsNº 131 / 238

ζ = 1 is critical damping

What is critical damping?

When the damping ratio hits 1, the system returns to rest as fast as possible without overshoot — less damps and it rings; more and it crawls.

Why it works

For mẍ + cẋ + kx = 0, ζ = c/(2√(km)). Critical damping is the boundary between oscillatory and exponential return.

When it fails

Critical damping is fastest to rest, not fastest to target. If you need to reach a value and can tolerate a small overshoot, ζ near 0.7 gets there sooner and is what most servo loops are tuned to. And it assumes a linear second-order system — add friction or a hard stop and ζ stops describing the behaviour at all.

Do it exactly

Estimate with the rule, then check it against the calculator that models it properly.

Open Mass-Spring-Damper →

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