On the Heads of Three Pins

A sphere of weight 100 N 100 \, \text{N} and radius 1 m 1 \, \text{m} has its center on the origin.

x = c o s θ s i n ϕ y = s i n θ s i n ϕ z = c o s ϕ \large{x = cos \theta \, sin \phi \\ y = sin \theta \, sin \phi \\ z = cos \phi }

The sphere is supported by three thin vertical pins which make contact at ( θ 1 , ϕ 1 ) = ( 0 , 2 π 3 ) (\theta_1, \phi_1) = (0, \frac{2 \pi}{3}) , ( θ 2 , ϕ 2 ) = ( π 3 , 3 π 4 ) (\theta_2, \phi_2) = (\frac{\pi}{3}, \frac{3 \pi}{4}) , and ( θ 3 , ϕ 3 ) = ( 4 π 5 , 5 π 6 ) (\theta_3, \phi_3) = (-\frac{4 \pi}{5}, \frac{5 \pi}{6}) .

What is the sum of the magnitudes of the three contact forces?

Note: Gravity is in the negative z z direction. Contact forces are normal to the surface.


The answer is 130.584.

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