Centre of Gravity vs Centroid: Understanding the Difference

by Yuvi K - January 2, 2024

In physics and engineering, the concepts of the centre of gravity and the centroid are fundamental in understanding the distribution of mass and geometry in objects. While they are often used interchangeably, they represent different but related concepts.

Centre of Gravity

• Definition: The centre of gravity (CG) of an object is the point where the total gravitational force on the body is considered to act. In other words, it’s the point of an object at which the weight is evenly dispersed and all sides are in balance.
• Dependence on Gravity: The CG depends on the gravitational field and can change if the object is in a different gravitational environment.
• Calculation: Determined by considering the distribution of mass in the object. For uniform gravity and symmetric bodies, the CG coincides with the geometric center.
• Applications: Important in fields like mechanical engineering, aeronautics, and biomechanics to ensure stability in structures, vehicles, and postures.

Centroid

• Definition: The centroid is a geometrical concept and is defined as the average position of all the points in a shape. It is the geometric center of a plane figure or object.
• Independence from Gravity: The centroid is a purely geometric property and does not depend on gravity. It remains constant regardless of the object’s environment.
• Calculation: Determined using principles of geometry and calculus, depending on the shape’s complexity.
• Applications: Used in civil engineering, architecture, and design to understand the structural integrity and behavior under loads.

Differences between Centre of Gravity and Centroid

1. Nature: CG is a physical concept linked to gravity, while the centroid is a purely geometrical concept.
2. Dependence: CG depends on the gravitational field, whereas the centroid does not.
3. Calculation: CG calculation involves the mass distribution, while the centroid is calculated using the shape’s geometry.
4. Consistency: For uniform objects under a uniform gravitational field, the CG and centroid coincide. However, this may not be the case for irregularly shaped objects or varied gravitational fields.

Conclusion

Understanding the distinction between the centre of gravity and the centroid is crucial in fields like physics, engineering, and architecture. While they may coincide in many practical situations, especially in uniform gravitational fields and symmetrical objects, they are fundamentally different concepts. The centre of gravity is essential for analyzing the stability and balance of objects, whereas the centroid plays a critical role in understanding the geometrical properties and structural integrity of objects.