Page:Popular Science Monthly Volume 75.djvu/27
A familiar form of gyrostat is shown in Fig. 8. It consists of a spinning wheel mounted in a metal ring which rests on a pivot 0. The pull of the earth on the wheel and ring produces an unbalanced torque about an axis which is at right angles to the axis of spin, and this torque causes the axis of spin to sweep around the pivot as described in connection with Fig. 7. Precessional motion is illustrated Fio. 8. Fig. 0. in the simplest kind of way by the ordinary top. Fig. 9 shows a top spinning about an inclined axis S. The weight of the top together with the reaction of the floor against the point of the top produces a torque the axis of which is at right angles to the plane of the paper acceleration (backwards acceleration r) forwards side viewi I front view Fio. 10. in Fig 9, and the effect of this torque is to cause the axis of spin to sweep around the vertical axis PP (the axis of precession). The above discussion furnishes a sufficient basis for the considera- tion of the various practical aspects of gyrostatic action, but it isinteresting to see how the precessional motion of the gyrostat in Fig.