A wire is in the shape of a unit circle centered on the origin, with the portion from to missing (see image). The wire's mass is , and gravity is in the direction.
A force is applied normally to the curve at all points on the curve, such that each unit of curve length experiences an infinitesimal force of the same magnitude:
In the above equation, the units on are . If the applied force keeps the wire in stasis, what is the value of ?
Note: My intent is to describe a constant linear pressure over the curve length
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You take an element of length d l and present at angle θ from the negative y axis. Now d l = r d θ . (r=1)
The upward force on this element would be d F c o s θ . Putting d F = α d l and integrating the upward force from 0° to 120°, doubling that to count in the second half, and equalling that to m g , would give us the value of α = √ 3 1 0 .