in TFMK. VELOCITY AND ACCELERATION 41 



product of the .acceleration (in feet per second per second) under 

 which it moves into the distance in feet it has travelled over. 



Easy examples on the application of these rules will be found 

 in the questions at the end of the chapter and in solving them 

 the student must carefully bear in mind that all the formulae 

 given in the chapter are equally applicable if the centimetre and 

 second, or other units, are adopted. 



CHIEF POINTS OF CHAPTER III. 



The Solar Day is the interval of time between the sun's highest 

 position on any one day to its corresponding position on the next 

 succeeding day. 



The Mean Solar Day is the quotient obtained by dividing the 

 length of the year measured by the sun by the number of days 

 in the year. Or, it is the average of the lengths of all the solar days 

 in the year. 



A Star or Sidereal Day is of constant length. It is the interval of 

 time between two succeeding southings of a star at any season of 

 the year. 



The Period of Eotation of the Earth. As the apparent motions of 

 the stars across the sky are produced by the rotation of the earth, 

 the exact time of rotation is determined by ascertaining the length 

 of the sidereal day. 



Units of Time. In physical measurements the unit of time 

 adopted is the mean solar second, that is, it is founded on the 

 average time required by the earth to make one complete rotation 

 on its axis relatively to the sun considered as a fixed point of 

 reference. 



The Velocity of a body is the rate at which it moves. Velocity 

 may be either uniform or variable. When a body's velocity is 

 uniform it moves over the same distance in every second. When 

 the velocity is variable unequal distances are moved over in equal 

 times. 



Uniform velocity - number of units of length travelled 

 number of units of time taken 



Acceleration is the rate of change of velocity. In measuring 

 uniform acceleration we must know what addition to or subtraction 

 from the velocity of the moving body there has been during each 

 second of its journey. 



Velocity. 



Uniform Variable 





Equal distances travelled 



over in equal times. Regular Irregular 



Acceleration, 



or rate of change 



of velocity. 



