In about 1915, Henry Sincosky of Philadelphia suspended...

In about 1915, Henry Sincosky of Philadelphia suspended himself from a rafter by gripping the rafter with the thumb of each hand on one side and the fingers on the opposite side (Fig. 6-19). Sincosky’s mass was 79 kg. If the coefficient of static friction between hand and rafter was 0.70, what was the least magnitude of the normal force on the rafter from each thumb or opposite fingers? (After suspending himself, Sincosky chinned himself on the rafter and then moved hand-over-hand along the rafter. If you do not think Sincosky’s grip was remarkable, try to repeat his stunt.)

In about 1915, Henry Sincosky of
Philadelphia suspended himself from a rafter by
gripping the rafter with the thumb of each hand on
one side and the fingers on the opposite side (Fig.
6-19). Sincosky’s mass was 79 kg. If the coefficient
of static friction between hand and rafter was 0.70,
what was the least magnitude of the normal force
on the rafter from each thumb or opposite fingers?
(After suspending himself, Sincosky chinned himself on the rafter and then moved hand-over-hand
along the rafter. If you do not think Sincosky’s grip
was remarkable, try to repeat his stunt.)

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Key Concepts

Load Distribution

Load distribution is the concept of how forces are shared among multiple points of contact or supports. In this context, the individual's weight is distributed between the two hands gripping the rafter, meaning that each hand must provide enough friction to support half of the total weight.

Equilibrium and Force Balance

Equilibrium and force balance involve ensuring that all forces acting on a system sum to zero, maintaining the system's state of rest. In hanging or gripping situations, the gravitational force must be counteracted by frictional and other support forces to achieve equilibrium.

Static Friction

Static friction is the force that arises between two contacting surfaces when they are at rest relative to each other. It prevents relative motion until an applied force exceeds a certain threshold, determined by the normal force and the coefficient of static friction.

Normal Force

The normal force is the reaction force exerted by a surface perpendicular to the object resting on it. In scenarios involving friction, the normal force directly affects the maximum static friction available, as it determines how forcefully the contacting surfaces press against each other.

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