RECAPITULATION. 447 



3. Relative space, is that part of absolute space 

 which is occupied by any body, and is compared 

 with any part occupied by another body. 



Motion. 



1 . Motion is also either absolute or relative. 



2. Absolute motion is the actual motion that 

 bodies have, independent of each other, and only 

 with regard to the parts of space. 



3. Relative motion is the degree and direction of 

 the motion of one body, when compared with that 

 of another. 



4. Accelerated motion is when the velocity of 

 the motion continually increases. 



5. Retarded motion is when the velocity conti- 

 nually decreases. 



6. The velocity of uniform motion is estimated 

 by the time employed in moving over a certain 

 space j or by the space moved over in a certain 

 time. 



7. To ascertain the velocity, divide the space 

 run over by the time. 



8. To know the space run over, multiply the 

 velocity by the time. 



9. In accelerated motion, the space run over is 

 as the square of the time, instead of being directly 

 as the time, as in uniform motion. 



10. A body acted upon by only one force, must 

 always move in a straight line. 



11. Bodies acted upon by two uniform forces, 

 whether equal or unequal, must also describe a 

 straight line. 



12. But if a body be acted upon by one uniform 

 force, or single impulse, and another accelerating 



