UNITS OF SECOND MOMENTS OF AREA The second moment of arcais Ax? If all lengths are in metres, then the result will be mºm = ml. bda For example in the formula the units are mm = m. 3 In typical engineering problems it is unlikely that dimensions of a cross- sectional area will be in metres. It is more probable that the units will be milli- metres, and if these are used the second moment of area will be in mm which will result in large numbers. In practice it is usual to calculate second moments of area in cm". This makes the arithmetic as simple as possible. @ : (214(2d-20)10) 10= 6.71*10-4 @ (2d+(2d-20)0*) xro-t2 = 0.84 x 10-6 Simplify and make equation and equation ® to zero in the form of : nd+ bd-c=0 equal to