Fig. 43.—HOOP.
860. Why does a "sucker" raise a stone?
Because underneath the sucker a vacuum is formed and the external air, pressing on all sides against the vacuum, lifts the stone. The term "sucker" is founded upon the mistaken notion that the leather "sucks," or "draws" the stone. That such is not the case is evident: if, when the stone is suspended, a pin's point be passed under the leather, so as to open a small passage for the air, the stone will drop instantly.
861. Why does a hoop roll, without falling to the ground?
Because the centrifugal force gives it a motion which is called the tangent to a circle—that is, a tendency in all its parts to fly off in a straight line. When a piece of clay adhering to the hoop flies off, it leaves the hoop in a line which is straight with the part of the surface from which it was propelled; this line is the tangent to the circle of the hoop; and the tendency of all the parts of the hoop to fly off in this manner, counteracts the attraction of the earth, so long as the hoop is kept in motion.
"Children obey your parents in all things: for this is well-pleasing unto the Lord."—Colossians iii.