List of second moments of area

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The following is a list of second moments of area of some shapes. The second moment of area, also known as area moment of inertia, is a geometrical property of an area which reflects how its points are distributed with regard to an arbitrary axis. The unit of dimension of the second moment of area is length to fourth power, L4, and should not be confused with the mass moment of inertia. If the piece is thin, however, the mass moment of inertia equals the area density times the area moment of inertia.

Second moments of area[edit]

Description Figure Area moment of inertia Comment
a filled circular area of radius r Moment of area of a circle.svg



[1]
an annulus of inner radius r1 and outer radius r2 Moment of area of an annulus.svg



For thin tubes, and . So, for a thin tube, .
a filled circular sector of angle θ in radians and radius r with respect to an axis through the centroid of the sector and the center of the circle Moment of area of a circular sector.svg This formula is valid only for 0 ≤
a filled semicircle with radius r with respect to a horizontal line passing through the centroid of the area Moment of area of a semicircle through the centroid.svg

[2]
a filled semicircle as above but with respect to an axis collinear with the base Moment of area of a semicircle through the base.svg

[2]
: This is a consequence of the parallel axis theorem and the fact that the distance between the x axes of the previous one and this one is
a filled quarter circle with radius r with the axes passing through the bases Moment of area of a quarter circle through the base.svg

[3]
a filled quarter circle with radius r with the axes passing through the centroid Moment of area of a quarter circle through the centroid.svg

[3]
This is a consequence of the parallel axis theorem and the fact that the distance between these two axes is
a filled ellipse whose radius along the x-axis is a and whose radius along the y-axis is b Moment of area of an ellipse.svg

a filled rectangular area with a base width of b and height h Moment of area of a rectangle through the centroid.svg

[4]
a filled rectangular area as above but with respect to an axis collinear with the base Moment of area of a rectangle through the base.svg

[4]
This is a result from the parallel axis theorem
a filled triangular area with a base width of b and height h with respect to an axis through the centroid Moment of area of a triangle through the centroid.svg

[5]
a filled triangular area as above but with respect to an axis collinear with the base Moment of area of a triangle through the base.svg

[5]
This is a consequence of the parallel axis theorem
An equal legged angle, commonly found in engineering applications Second Moment of Area Angle.jpg





is the often unused product of inertia, used to define inertia with a rotated axis
a filled regular hexagon with a side length of a Moment of area of a regular hexagon.svg

The result is valid for both a horizontal and a vertical axis through the centroid, and therefore is also valid for an axis with arbitrary direction that passes through the origin.

Parallel axis theorem[edit]

Parallel axis theorem.svg
Main article: Parallel axis theorem

The parallel axis theorem can be used to determine the second moment of area of a rigid body about any axis, given the body's moment of inertia about a parallel axis through the object's center of mass and the perpendicular distance (d) between the axes.

See also[edit]

References[edit]

  1. ^ "Circle". eFunda. Retrieved 2006-12-30. 
  2. ^ a b "Circular Half". eFunda. Retrieved 2006-12-30. 
  3. ^ a b "Quarter Circle". eFunda. Retrieved 2006-12-30. 
  4. ^ a b "Rectangular area". eFunda. Retrieved 2006-12-30. 
  5. ^ a b "Triangular area". eFunda. Retrieved 2006-12-30. 

External links[edit]