The rim tends to fly off from the centre of the wheel.
How is it prevented from flying off?
It is prevented by making the wheel very strong, so that all parts of it are held firmly together.
What does this centrifugal force sometimes cause?
The centrifugal force is so great that it sometimes causes grind-stones and mill-stones, when revolving rapidly, to burst into pieces.
What becomes of these stones when they burst?
When they burst, their pieces fly off in different directions, doing more or less injury to whatever obstructs their course.
When a horse turns a corner, why does the rider lean in the direction in which the horse is turning?
He leans so as to overcome the centrifugal force, and is thus prevented from falling off the horse.
How are cars prevented from running off the track, while turning a curve?