FALLING BODIES. 



59 



plane, consisting of a long ruler having a grooved edge, 

 down which a heavy ball was made to roll. In this way 

 he reduced the velocity, and diminished the interfering 

 resistance of the atmosphere without otherwise changing 

 the nature of the motion. 

 Let AB represent a plane so 

 inclined that the velocity of 

 a body rolling from B toward 

 A will be readily observable. 

 Let C be a heavy ball. The 

 gravity of the ball may be 

 represented by the vertical 

 line CD. But CD may be resolved into CF, which repre- 

 sents a force acting perpendicular to the plane and pro- 

 ducing pressure upon it but no motion at all, and CE, 

 which represents a force acting parallel to the plane, the 

 only force of any effect in producing motion. It may be 

 shown geometrically that 



EC : CD :: BG : BA. (Olnetfs Geometry, Art. 341.) 



By reducing, therefore, the inclination of the plane we 

 may reduce the magnitude of the motion producing com- 

 ponent of the force of gravity and thus reduce the velocity. 

 This will not affect the laws of the motion, that motion 

 being changed only in amount, 

 not at all in character. Jrl \\u 



122. Attwood's Device. 



For the purpose of lessening 

 the velocity of falling bodies 

 without changing the character 

 of the motion, Mr. Attwood 

 devised a machine which has 



FIG. 28. 



