# Effect of air resistance of the period of a pendulum [duplicate]

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Does air resistance increase or decrease the period of a simple pendulum?

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• A simple search gives : scirp.org/journal/PaperInformation.aspx?PaperID=73856 – user207455 Jun 15 at 8:22
• How can you define a period for a motion which is not periodic? – eranreches Jun 15 at 8:47
• @eranreches For damped simple harmonic motion where the displacement is $x = Ae^{-\beta t}\cos \omega t$, the period is defined to be $2\pi/\omega$. This corresponds to a "common sense" idea of the period if the damping is small, and is consistent with the definition when $\beta = 0$. – alephzero Jun 15 at 9:08

## 1 Answer

You can see that air resistance increases the period by a common-sense argument, without doing any maths.

Suppose the mass is at its maximum position, and moves to the central position in time $$t$$. If there is air resistance, the speed of movement of the mass will be less because the air resistance slows it down, and therefore $$t$$ will be larger.