CHAPTER VIII. 

 THE LEVER AND BALANCE. 



16. THE LEVEE. 



i. Balancing equal weights on a lever. (a) Make or obtain a lever consisting 

 of a strip of light wood graduated in centimetres, and having a thin ring 

 screwed into one edge, above the central point, and a hook screwed into each 

 end (Fig. 29). Hang the lever from a nail by the middle ring. If it does 

 not exactly balance, plane off a little wood from the end which sinks, or 

 slightly unscrew the hook at the end which rises above the horizontal, 

 until the lever does set itself horizontally. 



FIG. 29. A simple lever. 



Hang two pill-boxes or small linen bags by their strings from the lever, 

 one on each side of the fulcrum or pivot, at equal distances from it. Into 

 one of the bags place say 50 grams, and find how many grams you must 

 place into the other bag in order to restore equilibrium. Repeat the 

 experiment with the bags at a different distance. 



It will be found always that equilibrium is obtained when equal weights 

 are at equal distances from the turning point or fulcrum. 



ii. Principle of moments. (a) Place some pieces of lead in each of four 

 linen bags, and adjust by means of shot or small bits of lead until they 

 weigh respectively 50 grams, 100 grams, 200 grams, and 300 grams. Place 

 the 100 gram bag about 12 cm. from the fulcrum of the lever, and balance 

 it with a 50 gram bag on the other side. Record the distance from the 

 fulcrum in each case. Repeat the experiment by balancing 50 grams 

 against 100 grams, 50 grams against 200 grams, 100 grams against 300 grams 

 and other combinations. 



Record your observations in columns as below : 



38 



