. The Locomotive . Theside from which the dimension h is measured, as used in the table,is to be considered the base. Any rectangle up to 15 in height —one inch wide may have its moment of inertia read directly fromthe table, but if its width is not one inch, the moment may befound by multiplying the value in the table by the width of therectangle in inches. Sections which are not rectangular may oftenbe divided up into rectangles, and so may have their moments ofinertia calculated from the table by finding the moments of each ofthe parts by adding them together. As an example consider the Lsh
. The Locomotive . Theside from which the dimension h is measured, as used in the table,is to be considered the base. Any rectangle up to 15 in height —one inch wide may have its moment of inertia read directly fromthe table, but if its width is not one inch, the moment may befound by multiplying the value in the table by the width of therectangle in inches. Sections which are not rectangular may oftenbe divided up into rectangles, and so may have their moments ofinertia calculated from the table by finding the moments of each ofthe parts by adding them together. As an example consider the Lshaped figure in figure i. It may be considered as made up of tworectangles A B F G and C D E F. Suppose it is desired to obtainthe moment of inertia about the line G E which we will take as thebase of the figure. Suppose the height A G is 4 inches and thewidth A B ^ inch, also suppose the height A G is 4 inches and thethe height D E, ^^ inch. From the table it is seen that the moment 236 THE LOCOMOTIVE, [October,. of inertia of a rectangle 4inches long and one inchwide is Now sincethe rectangle A B G F isonly Yi, inch wide its mo-ment of inertia is half thisamount or Takingthe short leg of the L, arectangle ^ inch high andone inch wide has a momentof inertia of and one 2inches wide will be justtwice this amount or the moment of inertiaof the whole figure about theline G E would be -\ = ^0. ANOTHER CASE. Suppose now that it is de-FiG. I. sired to calculate the mo- ment of inertia of an angle iron like the one shown in figure 3 onpage 232 which has a hole i^ inches in diameter in the leg at thepoint where the section is taken. Figifre 2 shows how this sectionmay be split up into rectangles as AKJB, CIED and H G F will now proceed to get the moment of inertia of the sectionabout the line D F. Let us start with rectangle H G F E, Here theheight is ^ inch and from the table we see that the moment ofinertia for a rectangle ^ inch
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