184 



SIMPLE MACHINES 



Kite 



.String 

 FIG. 188. 



keel), while another part pushes the boat forward. The more efficient 

 the keel is, the less does the boat drift; the " closer " does it sail "to 

 the wind." 



208. The Kite. While in the sailboat the force of a 

 horizontal wind is changed partly to a force acting di- 

 rectly forward, in the kite a part of the 

 wind's force is made to act vertically 

 upward. If the kite (Fig. 188) is held 

 vertical, it gets all the force of the wind 

 that strikes it, and moves off in a hori- 

 zontal direction. This takes place when 

 why the wind Makes a the kite string breaks while the kite is in 



Kite Rise. 



the air. The kite is then only a falling 

 body (cf. 21), acted upon by the wind and by gravity. 

 If the kite were held horizontal, it would catch no 

 part of the wind, like a boat with its sail parallel with 

 the wind. But if the kite is inclined to the wind, the 

 force of the wind is divided into 

 two parts, one of which presses 

 against the kite, and is resisted 

 by the string; while the other 

 part acts vertically upward, and 

 raises the kite into the air. 



209. The Airship. Airships 

 may be of the balloon type 

 (Fig. 189), which rise because 

 they are filled with heated air or 



.. . , 



other light gases; or they may 

 be aeroplanes monoplanes, 

 biplanes, hydroplanes, etc. 



FIG. 189. 



One the first Di 



t 



to 



Stereograph 



