Lesson II. ] 



MECHANICS, 



P. It enables us to overcome a 

 ance, or move a weight, bearing on one 

 point, by applying a power to another. 



T. What are the parts of a lever on 



f the fulcrum called ? 

 P. The arm*. 



T. How many kinds of lever* are 

 there ? 



/'. Three, which vary according to the 

 relative situation of the power, fulcrum, 

 and weight 



28. T. How are these levers distin- 

 guished ? 



/'. Into a lever of the firtt kind, where 



the fulcrum is placed between the power 



and the weight ; a lever of the tecond kind, 



the weight is between the fulcrum 



of the third 



here the power is placed between 



rum and the weight. Fig. 2 is an 



example of a lever of the first kind. A B 



^ 



is termed the long arm of the lever, ni-.d 

 1* represents some 

 Mich as a hand drawing down the 

 rig arm at A, and, as t 



*--d to be weak or 



red with the resistance or 



arm must have a 



- relative length than the one to 

 he weight is attached. 



ve me some examples of levers 



P. When a poker i* 

 the bars of the fire-grate to raise tin 

 we have a f fa lever of 



\*a. (Fig. 8.) When we use a pin 

 from its shell, we 

 a lever of 



he Irvcr, and the hhell the fulcrum. 



ike of a pump is a lever of the 



'on nncl th<- pump-ro<U 



being ' be raised, and the luU 



Fio J A B P. the Irrrr. or Infltx, 

 < ihvoretirally rappoMd to b of 

 weight in every ,,rt ; F. DIP /-.. 

 MMT; n<l W. I>,P troy*/ Tl.o.r par- 



each tide of the fulcrum arc Uie armt of 



crum, the point on which it turns. A 

 common claw-hammer, employed to raise 



%.*> 



nails, is a lever of the first class; but, in 

 this case, the line of direction of the power 

 is perpendicular to the resistance. All 

 instruments for cutting or holding, which 

 are composed of two pieces crossing each 

 other in the midd 

 as sci- ft, pin- 



cers, pliers, nippers. &c., 

 are familiar 

 the pivot or joint being 

 the fulcrum, the resis- 

 tance or weight the pa- 

 per, grass, \'c. ID he 

 cut or seized, and the 

 ^ "*~~UT ^T. power applied hy the 

 - \ '\ hand. A common crow- 



JS . 3^ bar, applir.i to r:u-e 



ft?' * t stones or otht-r - 



is another familiar example ; the fulcrum 

 being another stone placed near to the one 

 to be raised, and the power 

 hands who raises it [S 



30. T. Are levers always straight ' 

 /*. No; they are sometimes cur, 

 in Fig. 5. The same advantage cai 



f. M 

 derived from a bent lever as from a straight 



3.-A, th pok.r. i,t bar. 



Is, or v*f< 



t Fig. 4. a, tb hind, or jwvr; . the nail, 

 md/. lh//rrnin 



r.rtW b9tr. .upPOMtd by 

 rnm F. Th wtifkl W, Is atuchtd 10 B 



