ELEMENTARY GENERAL SCIENCE 



CHAP. 



EXPT. 10. Fix one end of a piece of indiarubber cord, or 

 tubing, about two feet long, to a support. Stick two pins 

 through this cord about 18 inches apart. Tie 

 the lower end of the cord into a loop, and 

 then hang a weight by means of a hook from 

 it. Measure the distance between the pins 

 before and after putting on the weight. 

 Repeat the experiment with different weights. 

 You will notice that the cord can be stretched 

 or elongated, because the weights exert a 

 pulling force upon it. If a long metal wire 

 is used instead of the cord, the stretching 

 can be measured in a similar way, but it is 

 much less ; for instance, a brass wire ^- inch 

 in diameter and eleven feet long elongates 

 about 5\ inch when a weight of 28 Ibs. is pull- 



i\r * n ^. 



/ EXPT. 11. Procure a flexible wooden lath, 



and fix it horizontally by clamping one end 

 of it firmly. To the other end attach a pin 

 by means of a little wax. Place a rule verti- 

 cally near the pin, as in Fig. 3. A weight 

 should then be hung from the free end of 

 the lath, and the amount of bending observed. 

 Keeping the same weight, clamp the lath 

 so that only half the previous length can 

 be bent, and again notice the amount of 

 bending. Try also with other lengths. 



EXPT. 12. Suspend a wire with a weight at its lower end, 

 and under it a circle divided into degrees in a manner similar 



FIG. 2. Experiment 

 to illustrate the lon- 

 gitudinal stretching 

 of an india-rubber 

 cord. 



n 



D. 



Pia. 3. Measurement of the Bending of a Lath. 



