14 Gibson, Bodies floating in a Free or a Forced Vortex. 



centre of the vortex. Since, however, in virtue of 

 its revolution, the object makes one rotation per 

 revolution in the direction of revolution, the 

 absolute direction of rotation will usually be in the 

 same direction to that of revolution. 



This rotation, relative to the surrounding water, has 

 indirectly, an important bearing on the behaviour of the 



object. To realise this it must be remembered that, 

 other effects neglected, the body tends to gravitate to 

 the centre of the vortex, in virtue of the inward spiral 

 flow. But over the periphery aba (Fig.) the velocity of 

 the surrounding fluid is greater than that of the body, and 

 in virtue of the rotation of the body, this flow will be 

 deflected inwards towards the centre of the vortex. 

 Consequently the force accompan\'ing the change of 

 momentum of this passing stream of water will have an 

 mctivard radial component. Similarl)', since the portion 

 acd of the body is moving past its contiguous fluid this 



