162 LABORATORY LESSONS IN GENERAL SCIENCE 



3. Drag the same body along the table through the same 

 distance of 16 inches, and as accurately as possible get the 

 balance reading for the resistance overcome (and of the force 

 used in overcoming the resistance). In calculating the work 

 now done in moving the body, why is it not the same amount 

 of work as before? 



4. Calculate anew as in paragraphs 2 and 3 above, but 

 this time take the balance readings' in grams for whatever 

 body is used, and let the distance moved be in centimeters. 1 

 Let the product of the weight (force, or resistance), and the 

 distance (or space), be gram-centimeters of "work" (or of 

 "energy" used in doing the work). 



5. Express the number of grams above as kilograms, and 

 the number of centimeters as meters. 2 Then calculate the 

 amount of work done in kilogram-meters. 



CLASSES OF LEVERS 



1. By means of a lever clamp support a meter stick at 

 its middle point. Using loops of string over the ends of the 

 meter stick, support any small weight near one end, and 

 pull down sufficiently on the other end with a spring balance 

 to keep the bar (lever) horizontal. Move the weight (W) 

 to different distances from the point of support or fulcrum 

 (F), and in every case note and record both the balance 

 reading (P) and the distance from P to F. For several of 

 these positions of P and W get the product of P X Pd 

 (power-distance), and of W X Wd (weight-distance). These 



1 Balances and rulers should have both metric and English scales. 



2 One kilogram = 1000 grams, and one meter = 100 centimeters. 



