20 WELLS'S NATUKAL PHILOSOPHY. 



13. Why will a peebox, leaping from a carriage in rapid motion, fall in the direction in 

 which the carriage is moving at the moment his feet meet the ground f 



Because his entire body, on quitting the vehicle and descending to the 

 ground, retains, by its inertia, the progressive motion which it has in common 

 with it. When his feet reach the ground, they, and they alone, will be sud- 

 denly deprived of this progressive motion, by the resistance of the earth, but 

 the remainder of his body will retain it, and he wiU fall as if he were tripped. 



14. Why is a man standing carelessly in the stebn of a boat liable to fall Into the wat«r 

 behind, when the boat Degins to move ? 



Because his feet are pulled forward while the inertia of his lody keeps it a 

 the same position, and, therefore, behind its support. For a similar reason, 

 wheu the boat stops, the man is Uable to fall forward. 



15. When the sails of a ship are first spread to receive the fobce or impuibe of the wind, 

 why does not the vessel acquire her full speed at once ? 



Because it requires a httle time for the impelling force to overcome the tn- 

 trtia of the mass of the ship, or its disposition to remain at rest. 



16. Why, when the sails are taken in, does the vessel continue to move for a considerable 

 time? 



Because the inertia of the mass is opposed to a change of state, and the ves- 

 sel will continue to move until the resistance of the water overcomes the op- 

 position. 



17. Why do we kick against the door-post to shake the snow or dust from our shoes ? 

 The forward motion of the foot is arrested by the impact against the poet ; 



but this is not the case with respect to the particles of dust or snow which 

 are not attached to the foot, and are free to move. According to the laws 

 of inertia, they tend to persevere in the direction of the original motion, and 

 when the foot stops, they move on, or fly off. 



18. Why do we beat a coat or carpet to expel the dust? 



The cause which arrests the motion imparted to the coat or carpet by the 

 blow does not arrest the particles of dust, and their motion being continued, 

 they fly oS. 



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