"Choreboy" wrote

I weigh 230. At that pitch (26.5 degrees) I would have 206 pounds
perpendicular to the surface and 103 pounds of sheer. With rubber shoes
on clean pavement, the coefficient of friction could be about 1. On
that roof I'd need 0.5. (103/206 or 6/12).

The rope would be in case I step where I don't have quite that much
friction for a moment. If the rope supplied 30 pounds, friction would
have to supply only 73, for a coefficient of 0.35. A little extra pull
can make one more confident working near an eave on a weathered or dirty
roof.

A rope can also guarantee I won't have trouble with balance near the
edge. A pull of 30 pounds on a rope running over the ridge would mean
27 pounds on the ridge. I wonder what 27 pounds would damage.

"Hey! I was told there would be no math on this test!"

;-]