Define the radian.
A stone of weight 
is fixed, using glue, to one end P of a rigid rod CP, as shown in the figure below.
The rod is rotated about end C so that the stone moves in a vertical circle of radius 
. The angular speed 
of the rod and stone is gradually increased from zero until the glue snaps. The glue fixing the stone snaps when the tension in it is 
. For the position of the stone at which the glue snaps
on the dotted circle of the figure, mark with the letter S the position of the stone
calculate the angular speed of the stone.
.
