30 



THE HUMAN MOTOR 

 D 







H 



B 



FIG. 55. 



point K has a zero moment in relation to that point. But H 

 and P have the following moments : 



moment of H = H x El. 

 P = P x KO. 



In order that those two moments may be equal it is necessary 

 that 



H x El = P x KO, or KO - El x 



In proportion as the horizontal force H increases, KO must 

 increase, the limit being when KO = OB, half the thickness of 

 the wall ; then 



OB = El x S. ; 



the maximum horizontal effort H' will be 



OB 



H'= P X 



El 



The maximum moment, M = H 7 x El, is the moment of 

 stability of the wall. It will be seen that 



M = P X OB or ?- 



that is to say, the product of the weight by the semi-thickness 

 of the wall, or the product of the weight by the distance from 

 the side to the axis of gravity. 



