Calculating Moments: Finding M_{x} & M_{y} in Ellipse Bounded Region

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In summary, the conversation discusses finding the moments Mx and My for a region bounded by an ellipse. The speaker tried several methods, including drawing the ellipse and using specific bounds, but was unable to get the correct answers. They received a suggestion to change variables to center the ellipse around zero.
  • #1
City88
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Hi there...
I'm not sure how to go about finding the following moments:

[tex]
M_{x}= \int \int\ [/tex] y dx dy
[tex]
M_{y}= \int \int\ [/tex] x dx dy
Where the region is bounded by the ellipse:
[tex]\frac{(x-2)^2}{16}} + \frac{(y-4)^2}{36}}[/tex] = 1

I tried this several ways. I drew the ellipse and found the bounds to be
-2 [tex]\leq y[/tex] [tex]\leq10[/tex]
-2 [tex]\leq x[/tex] [tex]\leq 6[/tex]

Then I tried integrating with those bounds, but I can't seem to get the right answers. Any help/hints would be greatly appreciated.
 
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  • #2
Consider changing variables to center the ellipse around zero. eg:
u = x - 2
v = y - 4
 

1. What is the formula for calculating the moment of an ellipse bounded region?

The formula for calculating the moment of an ellipse bounded region is Mx = ∫ x² dA and My = ∫ y² dA, where x and y are the coordinates of the point and dA is the differential area element.

2. How do you find the coordinates of the centroid of an ellipse bounded region?

The coordinates of the centroid of an ellipse bounded region can be found using the formula (xc, yc) = (∫ x dA / A, ∫ y dA / A), where A is the area of the ellipse bounded region.

3. Can the moment of an ellipse bounded region be negative?

Yes, the moment of an ellipse bounded region can be negative. This occurs when the shape of the region is asymmetrical and the centroid is not located at the origin.

4. How does the moment of an ellipse bounded region change with respect to its orientation?

The moment of an ellipse bounded region is affected by its orientation. If the ellipse is rotated, the moments will also change. The moments will be equal if the ellipse is oriented at 45 degrees, and will be maximum or minimum when the ellipse is oriented parallel or perpendicular to the axes, respectively.

5. Can the moment of an ellipse bounded region be used to calculate its area?

No, the moment of an ellipse bounded region cannot be used to calculate its area. The moment is a measure of the distribution of mass within the region, while the area is a measure of the size of the region. Both values are unrelated and must be calculated separately.

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