Magnet on strap (also under Concepts > Rotational Dynamics)

Suppose a 50 gram magnet is 20 cm from the axis of rotation, with the strap moving at 50 degrees / second.

The magnet travels in a circular path of radius 20 cm.  The circumference of that path is 2 pi r = 2 pi * 20 cm = 40 pi cm, about 125 cm.

50 degrees is 50/360 of a complete rotation (360 deg for one rotation).

So during a 50 degree rotation the magnet moves 50/360 * 40 pi cm = 18 cm, roughly.

The magnet is therefore moving at about 18 cm/second.