GYROSTATIC ACTION 



33 



disk is to cause precession, the axis of spin of the disk in Figs. 26 and 

 27 turns towards the vertical, bringing the right-hand side (with 

 reference to the thrower) of the disk in Fig. 26 upwards and bringing 

 the left-hand side of the disk in Fig. 27 upwards. 



Fig. 28 represents a propeller-wheel boomerang. In the following 

 discussion the propeller is supposed to be right-handed, that is to say, 

 if it were set spinning in the direction of the curved arrow 8 in Fig. 

 28, it would blow air towards the reader like a desk fan. Fig. 28 

 represents the boomerang as it leaves the hands of the thrower, who 

 is supposed to be standing at MM, V being the direction in which the 

 boomerang is thrown, and the curved arrow S representing the direction 

 in which the boomerang is set spinning. The upper vane of the 



M 



M 



V-Sr 



side view 



Fig. 28. 



boomerang in Fig. 28 is traveling forwards at a greater velocity than 

 the lower vane, because the forward velocity of the upper vane is the 

 velocity of forward motion of the boomerang plus a forward velocity 

 Sr which is due to the spinning motion of the boomerang, whereas the 

 forward velocity of the lower vane is the forward velocity of the 

 boomerang minus Sr. Fig. 29 is a top view of the boomerang as it 

 leaves the hand of the thrower at M, V is the velocity of forward 

 motion of the boomerang, and the arrow S represents the spin of the 

 boomerang. The arrow F represents the force with which the air 

 pushes sidewise against the upper vane because of propeller action. 

 A force pushes sidewise in the same direction on the lower vane be- 

 cause of propeller action, but the sidewise force on the upper vane 

 is the greater because of the greater velocity of the upper vane. The 

 inequality of these forces constitutes a torque upon the boomerang, 

 and this torque is represented by the arrow T in Fig. 29. The effect of 



VOL. LXXV. — 3. 



