274 Introduction to the Study of Science 



IV. CURVES, INERTIA AND ITS EFFECTS 



113. Curves. Few roads are straight for a long distance, 

 usually having many curves, some of which are very sharp. 

 Country roads are not built at present for high speed, es- 

 pecially around turns, although on certain mountain roads the 

 sharpest curves are constructed to secure the safety of descend- 

 ing vehicles. Accidents occur because of the" attempt to take 

 improperly constructed curves at too great a speed. On 

 railroads, however, curves are designed and constructed to 

 secure both speed and safety. Trains make nearly the same 

 speed on ordinary curves as on straight track; but if the 

 track on such curves were as level as that of a street railway, 

 or the usual highway curves, disaster would certainly result 

 if attempted at high speed. 



114. Effect of change of direction. We may realize the 

 essential conditions that determine the construction of tracks 

 on curves for high speed, by referring to several common ex- 

 periences. If you are running along a straight path at top 

 speed and try suddenly to turn sharply to the right or left 

 without checking speed, you find that the path followed goes 

 far beyond the path intended and in the direction of the straight 

 course you are running. The momentum carries you beyond 

 the planned course. Bicycle riders or motor cyclists know 

 well how to maintain their balance in turning a corner or a 

 sharp curve in the road. They may reduce their speed some- 

 what, but frequently by leaning toward the inside of the curve 

 they take it safely at a fairly high speed. When throwing the 

 hammer, the thrower feels its pull outward, while he pulls it 

 inward ; when released the hammer flies off on what is called 

 a tangent. Many of you have swung a pail of water through 

 an inverted position without spilling a drop. The water tends 

 to go on a tangent, but is prevented by the pail and the inward 

 pull of the arm. 



