# Relationship between center of gravity and moment inertia a rectangle

### Parallel axis theorem - Wikipedia

The parallel axis theorem, also known as Huygens–Steiner theorem, or just as Steiner's The body has a moment of inertia Icm with respect to this axis. .. center of mass, and the last term is the total mass of the body times the square There is a useful relationship between the inertia matrix relative to the center of mass R. Moment of inertia ("MOI") is similar to inertia, except it applies to rotation rather than center of gravity, but only one axis is necessary to define moment of inertia. . Effects of Misalignment; Calculating Product of Inertia; Rectangular to Polar Conversion; Difference between CG Offset and Product of Inertia; POI Parallel Axis. Kinetics- It is the branch of dynamics which deals with the study of motion of bodies due to the C.G of a rectangle lies at the intersection of its diagonals. C.G of.

This leads to units of moment of inertia such as lb-in2, where the "lb" refers to the weight of the object rather than its mass. Correct units of moment of inertia or product of inertia are: Again, dimensional analysis will confirm if correct units are being used.

The following table shows some of the units in use today for moment of inertia and product of inertia: If moment of inertia or product of inertia are expressed in the following units, then their values can be used in engineering calculations as they are: Slug-ft2, lb-in-sec2, kg-m2, lb-ft-sec2, oz-in-sec2 RULE 2. If moment of inertia or product of inertia are expressed in the following units, then their values must be divided by the appropriate value of "g" to make them dimensionally correct.

Calculating the Moment of Inertia MOI, sometimes called the second moment, for a point mass around any axis is: The method of calculating radius of gyration is outlined in the following sections.

The reference axis is through a point equidistant from the two masses. Their combined MOI is therefore Mr2. The second example shows a thin walled tube of radius r.

By symmetry, the CG lies on the centerline of the tube. This leads to the definition: Rectangular Section Property The size of the beam is 0.

The moment of the inertia is calculated using the standard formula rectangular and the value is 0. And the centroid is 0.

M Moment of Inertia 0. The moment of the inertia is Calculated using the standard formula for circular and the value is 0.

## Parallel axis theorem

The calculated area of the section is 0. The moment of the inertia is calculated using the standard formula for triangle and the value is 0. And the centroid value is 0.

And the end condition will be simply supported. Here we omitted the material of the beam, because the discussion is only about the moment of inertia and centroid.

### Calculating Moment of Inertia: Real-World Problem Solving

These two properties are geometrical property so there is no need for the consideration of the material type and its properties. For the given load the bending moment is calculated.

Beam using either a rectangular, circular or triangular section, the maximum bending moment present in the beam will be Comparison of Moment of Inertia For rectangle, circle and triangle the calculated moment of inertia is compared to find which section will have more moment of inertia.

From figure 2, it will be very clear that the triangular section will carry much higher load carrying capacity, other than two sections. Thus if we were able to compute the clockwise moments of the particles of the rod with respect to the pivot point and knew the weight of the rod, we would then be able to compute the distance d from the pivot to the center of gravity.

Consider now a system of n point masses situated along a horizontal line, as shown in Fig. Suppose the weights of the masses are w1, w2, w3, Let M1 be the sum of the clockwise moments of the n masses with respect to the pivot point. Then the counterclockwise moment M2 due to F is given by Fd where d is the distance from the pivot to the center of gravity.

We lay an x-axis of a coordinate system along the rod with the origin at the pivot. We consider the rod to consist of an assemblage of particles m1, m2, The weight W of the rod is given by Since mass is proportional to weight, 3 can also be expressed in terms of mass.

In terms of mass it is where x is the distance of the infinitesimal element of mass dm from the pivot. We have considered a one-dimensional case where masses are distributed out in a line, as in a rod. The ideas are easily extended to assemblages of points in two and three-dimensional space. Consider a system of n point masses m1, m2, Again the point masses are conceived of as being attached to a rigid weightless framework.

**Moment of Inertia of L section**