The seconds hand of a clock completes one full revolution around
the face of the clock every minute.
One full revolution = 360 degrees.
The hand revolves (360 degrees / 60 seconds) = 6 degrees per second.
The tip of the hand travels in a circle, and covers the circumference
of the circle every minute. The circumference of a circle is
(2π) x (radius of the circle).
The length of the hand is the radius of the circle that it travels in,
so the circumference of the circle is
(2π) x (6.5 cm) centimeters.
The tip of the hand covers this distance in 60 seconds,
so its speed is
(13π cm) / (60 seconds) = 0.681 cm/sec.
