Centroids and Center of Gravity Examples

Eleven examples progress from symmetry and composite areas to distributed-load centroids and Pappus-Guldinus applications.

Centroid from Symmetry

A rectangular wall panel is 3.00 m3.00\ \text{m} wide and 2.40 m2.40\ \text{m} high. Locate its area centroid from the lower-left corner.

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Triangular Area Centroid

A triangular plate has a base of 6.00 m6.00\ \text{m} and altitude of 3.00 m3.00\ \text{m}. Determine the centroid height above the base.

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Centroid of a T-Section

A T-section consists of a 100×20 mm100\times20\ \text{mm} flange above a centered 20×80 mm20\times80\ \text{mm} web. Locate yˉ\bar{y} from the bottom.

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Rectangle with an Off-Center Circular Hole

A 200×100 mm200\times100\ \text{mm} rectangle has a circular hole of radius 20.0 mm20.0\ \text{mm} centered at x=150 mmx=150\ \text{mm} and y=50.0 mmy=50.0\ \text{mm}. Locate xˉ\bar{x} from the left edge.

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First Moment about the x-Axis

An area A=0.240 m2A=0.240\ \text{m}^2 has centroid coordinate yˉ=1.50 m\bar{y}=1.50\ \text{m}. Determine its first moment QxQ_x.

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Resultant of a Triangular Load

A load rises linearly from zero to 18.0 kN/m18.0\ \text{kN/m} over 6.00 m6.00\ \text{m}. Determine its equivalent force and line of action from the zero-intensity end.

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Pappus Volume of a Torus

A circular area of radius a=0.500 ma=0.500\ \text{m} is revolved about an external coplanar axis located R=2.00 mR=2.00\ \text{m} from the circle center. Determine the generated torus volume.

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Compare Centroid and Center of Mass

A geometrically symmetric rectangular panel is made from two equal-volume halves, but the left material has twice the density of the right. Will its geometric centroid and center of mass coincide?

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Centroid of an L-Shaped Area by Subtraction

An L-shaped area is formed from a 200×200 mm200\times200\ \text{mm} square by removing a 120×120 mm120\times120\ \text{mm} square from the upper-right corner. Locate the centroid from the lower-left corner.

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Resultant Location of a Trapezoidal Load

A load varies linearly from 4.00 kN/m4.00\ \text{kN/m} to 12.0 kN/m12.0\ \text{kN/m} over 5.00 m5.00\ \text{m}. Determine the equivalent force and its line of action from the 4.00 kN/m4.00\ \text{kN/m} end.

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Pappus Surface Area of a Torus

A circular curve of radius a=0.400 ma=0.400\ \text{m} is revolved about an external coplanar axis located R=1.50 mR=1.50\ \text{m} from the circle center. Determine the torus surface area.

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Reference Axes

Composite-centroid coordinates are meaningful only when every component centroid is measured from the same reference axes. Mixing local and global coordinates is a common source of errors.