MECHANICAL PARADOXES. 



This result of ordinary stick-throwing, how- 

 ever, would not be sufficient for the gyro- 

 scopic spin of the boomerang-thrower. The 

 shape of the implement enables him to in- 

 tensify this spin considerably at the moment 

 of despatching it. 



Look again at the outline of the boomerang 

 in Fig. 13. Suppose it to be thrown in the 

 general direction of the arrow E, from right 

 to left. Suppose it to be just on the point of 

 leaving the hand, which is underneath it, 

 with the thumb at C and the fingers at D. 

 As it is moving to the left, any obstacle at A 

 in front of the hinder horn would prevent that 

 horn, A K, from moving straight forwards in 

 the direction of the arrow E. To get past 

 the obstacle at A the rear end must move 

 sideways in the direction of the arrow G, and 

 in this direction the rear end is forced by the 

 impetus already acquired by the whole weapon. 

 But the centre of gravity of a weapon of this 

 shape is about the point F, and a sudden 

 movement given to one end of a long object 

 tends to make it revolve about its centre of 

 gravity, the other end moving in the opposite 

 direction. Therefore, when the rear end is 

 pushed towards G, the front end will move 

 in the direction of the arrow H. 



Now at the moment of discharge, when 

 the thumb is relaxed at C, the fingers remain 

 as an obstacle at D, and in order to get past 



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