136 INTRODUCTION TO GENERAL SCIENCE 



It must be remembered that the complete theory of the 

 aeroplane, or even of the kite, is much more complex than 

 has been stated, and many other factors enter into considera- 

 tion. It might be well to state that the effective area of a 

 plane increases with the velocity, since the air is forced more 

 to the sides; and curved planes give a greater component of 

 lift, due partly to reaction. 



Reference : 

 a. 1809 : 79. The Aeroplane. 



Experiment 52. To Make a Boomerang. 



Materials: Piece of pasteboard 6" square. 



a. Cut from the pasteboard a piece similar to a carpenter's 

 square, having both sides six inches long and one and one half 

 inches wide. Round the ends so that they are semicircles, 

 and round the outside angle, formed by the two sides, so that 

 it is a quarter circle. 



6. Place the boomerang on a book so that one end points 

 toward you and the other end projects at right angles to the 

 edge of the book. Incline the latter at an angle of 30 from 

 the horizontal, and hit the projecting end of the boomerang 

 a smart, straight blow with a pencil. 



After a few trials the boomerang can be made to go some 

 distance away and upwards, and then return to the feet of the 

 operator. 



This toy illustrates the first law of motion, in that it main- 

 tains its motion, revolving continually in the same plane. 

 The aeroplane glides through the air, and is prevented from 

 falling to earth, and, in fact, leaves the earth, by means of its 

 inclined planes, in much the same way as the boomerang 

 behaves. 



