256 MECHANICS 



secured in place with a rail brace at each tie. The laying of 

 the rails of the turnout is then continued. 



The rail MH is to be bent and spiked in place by laying 

 off offsets from the chord MH exactly as explained for stub 

 switches. The rail between M and H usually consists of two 

 pieces of plain rail bent to the proper curve. The outer rail 

 of the main track is not disturbed. 



Switch Timbers. Every first-class railroad has its own 

 standards for switches, which include the necessary switch 

 timbers. The number of ties and their lengths may be deter- 

 mined by the following rules: 



Rule I. To find the number of ties required for any switch 

 lead, reduce to inches the distance from the head-block to the 

 last long tie behind the frog, and divide this distance by the num- 

 ber of inches from center to center of ties; the quotient will be the 

 number of ties required. 



Rule n. Measure the length of the tie next the head-block and 

 the length of the last long tie behind the frog. Find the difference, 

 in inches, between them. Divide this difference by the number of 

 ties in the switch lead; the quotient will be the increase in length 

 per tie from the head-block toward the frog to have the ends of the 

 tie in proper line on both sides of the track. 



MECHANICS 



FALLING BODIES 



When the center of gravity of a moving body passes over 

 equal distances in equal intervals of time, the body has a 

 uniform motion; otherwise, the motion is variable. The 

 velocity in a uniform motion is constant and is equal to the 

 distance traversed by the center of gravity of the body in a 

 unit of time, as feet per second, miles per hour, etc. When, 

 in a variable motion, the velocity increases or decreases uni- 

 formly with the time, the motion is designated, respectively, as 

 uniformly accelerated or uniformly retarded, and the rate of 

 increase or decrease is called acceleration or retardation, being 

 equal to the amount that the velocity increases or decreases in 



