Volume of Revolution.
A solid object is generated by rotating two functions about the x-axis. The
created volume is determined by summing volumes of disks on
the x-axis from a to b. The disk volume (at every x position)
in turn is found by subtracting the inner disk volume from the
outer disk volume. The two equations express the generated volume.
An example of rotation is a rotating MusicBox flywheel giving an illusion of a translucent solid object.
