CENTRIFUGAL FORCE. 



21 



lower down, according to the rapidity of the stream and 

 the slowness of the boat. 



Another instance is afforded when a ferry-boat is 

 anchored, by means of a long rope, to a point some dis- 

 tance above (fig. 10) ; the boat, being tm-ned obliquely, 

 will pass from one bank to the other by the force of the 

 current. Here the water tends to carry the boat down- 

 Fig. 10. ward, while the 

 force of the rope 

 acts upward ; the 

 boat passes be- 

 tween the two 

 from bank to 

 bank. The ascent of a kite is precisely similar, the wind 

 and the string being counteracting forces. When a vessel 

 sails under a side wind, the resistance of the keel against 

 the water, and the force of the wind against the sail, act 

 in different directions, and produce a motion of the vessel 

 between them. 



CENTRIFUGAL FORCE. 



All bodies, when in motion, have a tendency to move 

 forward in a straight line. A stone thrown into the air is 

 gradually bent from this straight course into a curve by 

 the attraction of the earth. When a ball is shot from a 

 gun, the force being greater, it flies in a longer and 

 straighter curve. A familiar example also occurs, while 

 driving a wagon rapidly, in attempting to turn suddenly 

 to the right or left ; the tendency of the load to move 

 straight on will sometimes cause its overthrow. An 

 observance of this principle would prevent the error which 

 some commit by making sharp turns or angles in ditches 

 and water-courses ; the onward tendency of the water 

 drives it against the bank, checks its course, and wears 

 away the earth. By giving the ditch a curve, the water 



