Derivation of formula of centroid

In summary, the integral of y' is zero because it is measured from the centroid, where each value of y' dA is canceled by -y' dA. This means that y-bar, when measured from the centroid, is equal to zero. Additionally, the integral of y'^2 dA is just the moment of inertia about the center of mass, which is Ix. Therefore, in the first integral, y' is squared and does not cancel out because it is always positive.
  • #1
werson tan
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Homework Statement


what is y ′and y bar ? why y ′ is changed to y bar ? why are they = 0 ?

Homework Equations

The Attempt at a Solution

 

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  • #2
The middle integral is zero because y' is measured w.r.t. to the centroid so that
each value of y' dA is canceled by -y' dA by definition of a centroid or in other
words y-bar = zero when measured from the centroid.
Also, since y' is measured from the centroid then the integral of y'^2 dA is just
the moment of inertia about the center of mass which is Ix.
 
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  • #3
J Hann said:
The middle integral is zero because y' is measured w.r.t. to the centroid so that
each value of y' dA is canceled by -y' dA by definition of a centroid or in other
words y-bar = zero when measured from the centroid.
Also, since y' is measured from the centroid then the integral of ^2 dA is just
the moment of inertia about the center of mass which is Ix.
in the first integral , the
J Hann said:
The middle integral is zero because y' is measured w.r.t. to the centroid so that
each value of y' dA is canceled by -y' dA by definition of a centroid or in other
words y-bar = zero when measured from the centroid.
Also, since y' is measured from the centroid then the integral of y'^2 dA is just
the moment of inertia about the center of mass which is Ix.
in the first integral , the y prime is squared , so they don't cancel out each other?
 
  • #4
werson tan said:
in the first integral , the

in the first integral , the y prime is squared , so they don't cancel out each other?
When have you squared a real number and it came out negative?
 

Related to Derivation of formula of centroid

1. What is the formula for finding the centroid of a shape?

The formula for finding the centroid of a shape is:
x̄ = (∑(xi * Ai)) / A
ȳ = (∑(yi * Ai)) / A
where x̄ and ȳ represent the x-coordinate and y-coordinate of the centroid, xi and yi represent the x and y coordinates of each individual point, Ai represents the area of each individual point, and A represents the total area of the shape.

2. How is the centroid of a triangle calculated?

The centroid of a triangle can be calculated using the formula:
x̄ = (x1 + x2 + x3) / 3
ȳ = (y1 + y2 + y3) / 3
where (x1, y1), (x2, y2), and (x3, y3) represent the coordinates of the three vertices of the triangle.

3. What is the significance of the centroid in geometry?

The centroid of a shape is the point where all the medians intersect. This point divides each median into two parts, with the distance from the centroid to the vertex being twice the distance from the centroid to the midpoint of the opposite side. The centroid has many important properties in geometry, such as being the center of mass and the center of gravity of a shape.

4. Can the centroid be outside of the shape?

Yes, the centroid can be outside of the shape. This is possible when the shape is irregular and does not have symmetrical sides. In this case, the centroid may lie outside of the shape, but it will still divide the shape into equal areas.

5. How is the centroid of a compound shape calculated?

The centroid of a compound shape can be calculated by finding the individual centroids of each component of the shape and then using the formula for a weighted average to find the overall centroid. This involves finding the area of each component, multiplying it by the distance of its centroid from a chosen reference point, and then dividing the sum of these values by the total area of the compound shape.

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