WHAT KEEPS THE BICYCLER UPRIGHT? 



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ZI_ 



i 



B 



Fig. 5.- 



C 



Diagram illustrating the Com- 

 position of Forces. 



Others find in its going so fast the reason why the bicycle does 

 not fall referring, of course, in a blind way to that principle em- 

 bodied by Newton in his first law : " A body in motion, if left to 

 itself, will continue to move in a straight line forever." A brief 

 examination will, I think, convince you that this, too, fails to 

 account for the effect which we know is somehow produced. 



It is another principle in phys- 

 ics that two forces acting at right 

 angles to each other do not inter- 

 fere. Each produces its own effect 

 as fully as if the other did not act. 

 For example, if a certain force 

 sends a body (D, Fig. 5) north at 

 the rate of ten feet in a second, and 

 another force sends it east at the 

 same rate, at the end of one second 

 it will have gone ten feet north and 

 ten feet east, exactly as if each force D 

 had acted alone. Going toward A B 

 does not in the least hinder its go- 

 ing toward B C Now, in case of a bicyclist, his forward motion, 

 whether fast or slow, is at right angles to gravity, hence does not 

 in any way resist it ; and, therefore, as it is gravity that causes 

 him to tilt over, the forward motion will not prevent his falling. 



But it may be said that the force of gravity when the 'cycle 

 leans, say to the right, is in fact resolved into two components, 

 one vertical and the other lateral, and it is the latter only that 

 causes the bicyclist to fall. This does not help the matter, for 

 both components are perpendicular to the course of the bicycle, 

 and hence its forward motion can in no way counteract either of 

 them. Unless some other force comes into play, the bicyclist must 

 fall toward whichever side he happens to begin to lean. 



Many think they find this counteracting influence in " centrif- 

 ugal force." You all are familiar with the effects of this " force." 

 You feel them every time you turn a corner quickly, whether on 

 foot or in a wagon, or on horseback. The bare-back riders in the 

 circus lean well toward the center of the ring, to escape being 

 thrown outward. We see its effect when the bicyclist spins around 

 a corner. In such cases " centrifugal force " plays an important 

 part, and is the real upholding force. 



But centrifugal force is impossible so long as the body moves 

 in the same direction i. e., in a straight line. There must be 

 change of direction, and, other things being equal, this force is 

 greater in proportion to the abruptness of that change ; or, as 

 mathematicians say, the velocity being constant, it varies in- 

 versely as the radius of the curve in which the body moves. The 



