Math CentralQuandaries & Queries


Question from Janna:

How do I find the total length of a piece of rope formed in a semicircle that has a diameter of 8 inches?

Hi Janna,

The circumference of a circle of diameter $d$ inches is $\pi \; d$ inches and you want half of this.

rope in a semicircle

In my diagram above the brown rope is formed in a semicircle but the length of the outside of the semicircle is larger than the length of the inside of the semicircle. To make sure the rope reaches around the semicircle you should take the diameter to be $d + 2\times t$ inches where $t$ is the thickness of the rope.


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