LAWS OF MOTION 57 



increase at a uniform rate. This uniform increase in speed 

 is called the acceleration of gravity. It is expressed in feet 

 per second per second. 



When a body falls freely in this manner it will have attained 

 at the end of one second a velocity of 32.2 ft. per second. 

 Thus the average velocity during the first second will be 

 16.1 ft. per second. Since the velocity increases at a uni- 

 form rate, it will be 64.4 ft. per second at the end of 2 seconds, 

 and the space fallen through during this second second will 

 be 48.3 ft, 



The average velocity of the object for any second is the average 

 of the velocity at the beginning and the velocity at the end of 

 that second. 



Thus: 



Velocity at beginning of 1st sec. = 00.0 ft. per sec. 

 Velocity at end of 1st sec. - 32.2 " " " 



2)32.2 

 Average velocity for 1st sec. 16.1. " " " 



Velocity at beginning of 2nd sec. = 32.2 " " " 

 Velocity at end of 2nd sec. - 64.4 " " " 



2)96.6 

 Average velocity for 2nd sec. = 48.3 " " " 



Velocity at beginning of 3rd sec. = 64.4 " " " 

 Velocity at end of 3rd sec. 96.6 " " " 



2)161.0 

 Average velocity for 3rd pec. 80:5 " ' " 



As the space fallen through in any given second is equal 

 to the average velocity for that second, it follows that the 



