GYROSTATIC ACTION 



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the handle bar is turned, and although this gyre-static action helps to 

 maintain the equilibrium of the rider, it is very small in its effect as 

 compared with the linear momentum of the rider and bicycle frame. 



Fig. 24 is a top view of an axle 

 and pair of drive wheels of a locomo- 

 tive rounding a railway curve. The 

 arrow S in the vector diagram repre- 

 sents the spin-momentum of the axle 

 and drivers at a given instant, 8' rep- 

 resents the spin-momentum at a later 

 instant, A# represents the increment 

 of spin-momentum, and T represents 

 the torque which must act upon the 

 axle because of its precession. To 

 exert this torque the outer rail must 

 push up with an excessive force against 

 the outer driver, or, in other words, 

 the outer driver must be forced down- 

 wards against the outer rail with more 

 force than that which is due to the 

 locomotive alone as it is rounding a 

 curve. That is to say, the gyrostatic action of the drivers of a loco- 

 motive exaggerates the excess of pressure on the outer rail while the 

 locomotive is rounding a curve. 



Gyrostatic Action of the Boomerang 

 The most familiar type of boomerang is a pair of crossed sticks 

 twisted very slightly at the ends like the vanes of a windmill. This 

 type of boomerang, which we will call the propeller-wheel type, is 

 essentially similar in its action to the boomerang of the native Austral- 

 ians. The boomerang is thrown through the air with a spinning 

 motion about an axis at right angles to the plane of the crossed pair 

 of sticks, and the peculiar flight of the boomerang is due to the forces 

 exerted upon the boomerang by the air. 



Forces are exerted upon the moving boomerang very much as if it 

 were a disk traveling approximately edgewise through the air and forces 

 are exerted upon the boomerang by virtue of its propeller-wheel shape 

 and because of its combined spinning and edgewise motion. The 

 effects of these two sets of forces will be described separately and their 

 combined action will then be made use of in explaining the actual 

 motion of the boomerang. 



A disk moving approximately edgewise through the air is in an 

 unstable condition, if the disk starts to glance to one side or the other 

 the air exerts a turning force or torque upon it which tends to turn 



