Moment that Inertia that Triangle

If you space interested in the mass moment of inertia the a triangle, please usage this calculator. The current page is around the cross-sectional moment of inertia (also called second moment that area).

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This device calculates the minute of inertia i (second minute of area) of a triangle. Go into the form dimensions "b" and "h" below. The calculated outcomes will have the very same units as your input. Please use consistent units for any type of input.

Ix Iy and also Ixy Parallel come x Parallel come y Rotated x Rotated x with balance out Through a allude Principal Triangle info




The minute of inertia of a triangle with respect to an axis passing v its centroid, parallel to its base, is given by the complying with expression:

ns = fracb h^336

where b is the base width, and specifically the triangle side parallel to the axis, and also h is the triangle height (perpendicular come the axis and the base).

The minute of inertia that a triangle with respect come an axis passing v its base, is offered by the complying with expression:

ns = fracb h^312

This deserve to be verified by application of the Parallel Axes to organize (see below) because triangle centroid is located at a distance equal come h/3 native base.

The minute of inertia of a triangle through respect come an axis perpendicular come its base, have the right to be found, because axis y"-y" in the figure below, divides the initial triangle right into two right ones, A and B. These triangles, have typical base equal to h, and also heights b1 and also b2 respectively. Hence their linked moment the inertia is:

I_y" = frach b_1^312 + frach b_2^312

Taking right into account the b_2=b-b_1 and also that centroidal parallel axis y-y is at a distance frac23(fracb2-b_1) from y"-y" makes possible to discover the minute of inertia Iy, using the Parallel Axes theorem (see below). After ~ algebraic manipulation the last expression is:

I_y = frach b36(b^2-b_1 b + b_1^2)



Parallel Axes Theorem

The minute of inertia of any type of shape, in respect come an arbitrary, no centroidal axis, have the right to be found if its minute of inertia in respect to a centroidal axis, parallel come the very first one, is known. The so-called Parallel Axes theorem is provided by the complying with equation:

I" = ns + A d^2

where I" is the minute of inertia in respect come an arbitrary axis, i the minute of inertia in respect to a centroidal axis, parallel come the first one, d the distance in between the two parallel axes and also A the area the the shape (=bh/2 in case of a triangle).

For the product that inertia Ixy, the parallel axes theorem take away a similar form:

I_xy" = I_xy + A d_xd_y

where Ixy is the product the inertia, relative to centroidal axes x,y, and also Ixy" is the product of inertia, relative to axes that are parallel to centroidal x,y ones, having actually offsets from them d_x and d_y respectively.

Rotated axes

For the change of the moment of inertia from one system of axes x,y to one more one u,v, rotated by an angle φ, the following equations are used:

eginsplit I_u & = fracI_x+I_y2 + fracI_x-I_y2 cos2varphi -I_xy sin2varphi \ I_v & = fracI_x+I_y2 - fracI_x-I_y2 cos2varphi +I_xy sin2varphi \ I_uv & = fracI_x-I_y2 sin2varphi +I_xy cos2varphi endsplit

where Ix, Iy the moment of inertia about the early stage axes and Ixy the product of inertia. Iu, Iv and Iuv room the respective amounts for the rotated axes u,v. The product the inertia for a triangle is normally nonzero, uneven symmetry exists. It deserve to be found, considering the two right triangles A,B in the figure below. Their linked product the inertia relative to axes x0,y0 is:

I_x0y0 = -fracb_1^2 h^224 + fracb_2^2 h^224

Taking into account that suggest 0 ranges from centroid are d_x = -frac23(fracb2-b_1) and also d_y = -frach3 , the product the inertia Ixy loved one to centroid deserve to be found, making use of the Parallel Axes Theorem.


A basic purpose calculator for the change of the moments of inertia and the product of inertia, of any kind of 2D shape, due to axis rotation, is obtainable here.

Principal axes

In principal axes, that are rotated by an angle θ family member to original centroidal persons x,y, the product of inertia i do not care zero. Since of this, any kind of symmetry axis the the shape, is additionally a major axis. The moments of inertia around principal axes, I_I, I_II are called principal moment of inertia, and are the maximum and also minimum ones, for any angle that rotation that the name: coordinates system. If Ix, Iy and also Ixy are well-known for the arbitrarily centroidal coordinate device x,y, then the primary moments of inertia and also the rotation angle θ the the principal axes have the right to be found, v the next expressions:

eginsplit I_I,II & = fracI_x+I_y2 pm sqrtleft(fracI_x-I_y2 ight)^2 + I_xy^2 \ an 2 heta & = -frac2I_xyI_x-I_y endsplit

You can calculate the major moments of inertia, making use of our pertinent calculator, easily accessible here.


The dimensions of minute of inertia (second moment of area) room ^4 .

Mass minute of inertia

In Physics the term moment of inertia has a various meaning. It is associated with the mass circulation of things (or multiple objects) about an axis. This is various from the meaning usually provided in Engineering techniques (also in this page) as a residential property of the area that a shape, generally a cross-section, about the axis. The term second moment the area seems an ext accurate in this regard.


The moment of inertia (second minute or area) is provided in beam theory to describe the rigidity that a beam against flexure (see beam bending theory). The bending moment M applied to a cross-section is related with its moment of inertia with the following equation:

M = E imes i imes kappa

where E is the Young"s modulus, a residential property of the material, and κ the curvature of the beam as result of the used load. Beam curvature κ explains the extent of flexure in the beam and can be expressed in regards to beam deflection w(x) along longitudinal beam axis x, as: kappa = fracd^2 w(x)dx^2 . Therefore, it deserve to be viewed from the former equation, that as soon as a details bending minute M is applied to a beam cross-section, the emerged curvature is reversely proportional come the moment of inertia I. Integrating curvatures end beam length, the deflection, at some allude along x-axis, should additionally be reversely proportional to I.

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