Page:Popular Science Monthly Volume 75.djvu/34

30 where the arrows FF in the top view represent the forces with which the bearings must act upon the engine shaft to produce the torque T.

Fig. 23 represents a penny rolling along a floor. The forces FF in the side view (the tendency of the penny to fall over) constitute a torque which is represented by the arrow T in the top view. This torque produces during a short interval of time an increment of spin-momentum

&#916;S which, added to the existing spin-momentum S, gives the resultant spin-momentum S' in the direction of which the axis of the penny is found to be turned. The result is that the penny rolls along a circular path as represented by the dotted curve in the top view, Fig. 23. The wheels of a bicycle exhibit a gyrostatic reaction when