Calculating Ixy | Plane ABCD, PQRS Symmetry & Moment of Area

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First, calculate Ixy for a rectangle with respect to its own centroid and then use the formula Ixy = Ixc + A*d^2 where Ixc is the value of Ixy for the rectangle with respect to its centroid, A is the area of the rectangle, and d is the distance between the centroids of the two rectangles. This will give you the Ixy for the rectangle PQRS. In summary, for any plane figure with an axis of symmetry, Ixy will be zero for coordinate axes through the centroid of the figure. To calculate Ixy for a rectangle like PQRS, use the parallel axis theorem.
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phydis
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Here as shown in the diagram,

(1)Is Ixy zero for plane ABCD symmetrical along X axis? If yes, how it happens?
(2)How can we calculate Ixy for the plane PQRS ?

Ixy = the product of moment of area.

Thanks!
 

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For any plane figure with an axis of symmetry, Ixy = 0 for coordinate axes thru the centroid of the figure.

To confirm this, examine the definition of Ixy = Int(x*y)dA For every element of area dA which lies on one side of the axis of symmetry, there will be a corresponding element of area lying on the opposite side which is the same distance from the axis. When you add up all of these elements of area multiplied by x*y, the integral is necessarily equal to zero.

To calculate the Ixy of rectangle PQRS, apply the parallel axis theorem.
 
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FAQ: Calculating Ixy | Plane ABCD, PQRS Symmetry & Moment of Area

How do you calculate the moment of inertia for a plane with ABCD symmetry?

To calculate the moment of inertia for a plane with ABCD symmetry, you would first need to determine the centroid of the plane. This can be done by finding the average of the x and y coordinates for each vertex of the plane. Once you have the centroid, you can use the formula Ixy = ∑(x²+y²)dA, where x and y are the distance from the centroid and dA is the differential area. Integrate this formula over the entire area of the plane to get the moment of inertia.

What is the significance of PQRS symmetry in calculating Ixy?

PQRS symmetry refers to the symmetry of the plane about the x and y axes. This means that the plane can be divided into four equal parts that are reflections of each other. This symmetry allows us to simplify the calculation of Ixy by only considering one quarter of the plane and then multiplying the result by four.

Can I use the same formula to calculate Ixy for any shape with ABCD symmetry?

Yes, the formula Ixy = ∑(x²+y²)dA can be used to calculate Ixy for any shape with ABCD symmetry. However, you may need to break down the shape into smaller, simpler shapes in order to perform the integration.

How does the value of Ixy change with respect to the orientation of the plane?

The value of Ixy will change depending on the orientation of the plane. This is because the distance from the centroid to each point on the plane will vary depending on the orientation. The closer the points are to the centroid, the smaller the value of Ixy will be.

What are some real-life applications of calculating Ixy?

Calculating Ixy is important in engineering and physics, as it helps us understand the distribution of mass and the rotational stability of an object. It is used in the design and analysis of structures, such as buildings, bridges, and airplanes. It is also used in calculating the moment of inertia for rotating objects, such as wheels and propellers. Additionally, Ixy is important in understanding the behavior of materials under bending and torsion forces.

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