CHAPTER IV. 



SOME PROPERTIES OF SOLID BODIES INERTIA MOTION FRICTION THE 



PENDULUM EQUILIBRIUM. 



THOSE who have followed us through the preceding pages have now, we hope, 

 some ideas upon Gravity and the Forces of Nature. In speaking of Forces 

 we said " Force was a cause of Motion." Let us now consider Inertia, and 

 Motion with its accompanying opponent, Friction. 



Fig. 29. Shock communicated by elasticity. 



INERTIA is the passiveness of Matter. This perfect indifference to either 

 rest or motion makes the great distinction between living and lifeless matter. 

 Inertia, or Vis Inertia, is this passiveness. Now, to overcome this indif- 

 ference we must use force, and when we have applied force to matter we set it 

 in motion ; that is, we move it When we move it we find a certain resistance 

 which is always proportionate to the force applied. In mechanics this is 

 termed Action, and Reaction, which are always equal forces acting in opposite 

 directions. This is Newton's law, and may be explained by a " weight " on 

 a table, which presses against the table with the same force with which 



