1.4 Why does a rotating ball curve

Why does a rotating ball curve? In the case of an unrotating ball, Fig. 1.2(a) shows air flow around a ball. Suppose the atmosphere is perfectly calm and the ball doesn't have any outside force, then the ball should be go straight. Actually, the ball, which is received complex force of hydrodynamics like Karman's vortex street, could not go straight, the locus is as knuckle ball or fork ball. But we intend to ignore the complex force in this web site.

Fig.1.2(a) Flowing air around a unrotating ball

A ball that is hovering and spinning whirls the surroundeding air due to the friction between the ball and the air. Fig.1.2(b)

Fig.1.2(b) Flowing air around a rotating ball

A ball gradually loses energy because it is being dragged by the surrounding air. A ball's rotation speed decreases. Please pay attention to the flowing air which is whirled using energy of rotating ball. If I can express it another way, if there is no friction between a ball and the air, then the surrounding air will not be whirled.

Fig.1.2(c) is a composite of Fig.1.2(a) and Fig.1.2(b). A flying ball while rotating is curved by force of 'F' in Fig.1.2(c). An effect of such force is basically the same as lifting one of airplane wing.

Fig.1.2(c) Flowing air around a flying ball while rotating

You may have deduced why I used a rotating ball in atmosphere to demonstrate my point. If so, you have good sixth sense. In fact, the motion of a top and the motion of a rotating ball is very similar. Please consider the motion of a top again. Could it say that the movement of a top is affected by the interaction between the rotating gravitational field of a top and the gravitational field of the earth?

Next, let's go to the chapter, 'What meaning controlling gravity is'.

Updated 10/Oct/1996 redsky@graveng.jp