# Centre of Gravity vs. Centroid: What's the Difference?

Edited by Aimie Carlson || By Harlon Moss || Published on February 6, 2024
Centre of gravity is the point where gravitational force acts on a body, while centroid is the geometric center of a homogeneous object.

## Key Differences

The centre of gravity is a point where the total gravitational force on an object appears to act. It's dependent on the shape and the gravitational field. In contrast, the centroid is the geometric center of an object, determined purely by its shape and size, irrespective of the gravitational field or material composition.
Centre of gravity is crucial in understanding the stability and balance of an object under the influence of gravity. It changes with the object's orientation in a gravitational field. Conversely, the centroid is a fixed property of a shape, constant regardless of orientation and not influenced by external forces.
In uniform gravitational fields and for homogenous objects, the centre of gravity coincides with the centroid. However, for non-homogeneous objects or in varying gravitational fields, the centre of gravity and centroid can be at different locations.
The concept of centre of gravity is vital in physics and engineering for analyzing the behavior of objects under gravity. Centroid, on the other hand, is a concept used in geometry, engineering, and calculus to identify the mean position of all points in a shape.
Calculating the centre of gravity involves considering the mass distribution of an object along with gravitational influence, whereas finding the centroid involves geometric calculations based on the shape and dimensions of the object, without consideration of mass or gravity.

## Comparison Chart

### Definition

Point where gravitational force acts on a body.
Geometric center of a homogeneous object.

### Dependency

Depends on mass distribution and gravitational field.
Solely based on geometry of the object.

### Changes with Orientation

Can change with orientation in a gravitational field.
Constant, regardless of orientation.

### Relevance in Fields

Important in physics and engineering.
Significant in geometry and engineering.

### Coincidence in Uniform Conditions

Coincides with centroid in uniform objects in uniform fields.
Always at the same point for a given shape.

## Centre of Gravity and Centroid Definitions

#### Centre of Gravity

A point where the weight of a body or system is concentrated.
Balancing a pencil on your finger finds its centre of gravity.

#### Centroid

A point representing the mean position of the matter in a body.
The centroid of a rectangular card is at the intersection of its diagonals.

#### Centre of Gravity

The point in a body around which the resultant torque due to gravity forces vanishes.
A seesaw balances at the centre of gravity of the combined weight of the children.

#### Centroid

The center of mass of a geometric object of uniform density.
In a uniform density rod, the centroid is at its midpoint.

#### Centre of Gravity

A point where all the mass of a body or system can be considered concentrated.
The centre of gravity of a car affects its stability and handling.

#### Centroid

A point where a shape's dimensions balance perfectly.
The centroid of a semicircle is nearer to its base than its curved edge.

#### Centre of Gravity

Point of an object where the gravitational force can be considered to act.
The centre of gravity of a ring is at its center, where no material exists.

#### Centroid

The average position of all points in a shape.
The centroid of a circle is at its center, equidistant from all points on the perimeter.

#### Centre of Gravity

A single point representing the combined effect of gravity on an object's mass.
In space, an astronaut’s centre of gravity helps determine their orientation.

#### Centroid

The geometric center of a plane figure or solid body.
The centroid of a triangle is the point where its medians intersect.

#### Centroid

See center of mass.

## FAQs

#### Do the centre of gravity and centroid always coincide?

They coincide in uniform objects under uniform gravitational fields.

#### What is the centre of gravity?

It's the point where the gravitational force acts on an object.

#### How is the centroid determined?

Through geometric calculations based on the shape and size.

#### Can the centre of gravity be outside the material of an object?

Yes, like in a ring or a hollow sphere.

#### Is the centroid always within the material of an object?

Yes, it's a geometric property of the shape.

#### How is the centre of gravity calculated?

By considering the mass distribution and the gravitational influence.

#### What is a centroid?

The geometric center of a homogeneous object.

#### Why is the centre of gravity important?

It's crucial for understanding the stability and balance under gravity.

#### In what fields is the centroid a key concept?

Geometry, engineering, and calculus.

#### Does the centroid change with orientation?

No, it's a constant property of the shape.

#### What role does the centre of gravity play in engineering?

It's vital for design and analysis of structures and vehicles.

#### How does the centroid assist in engineering?

It helps in the analysis of stress, strain, and fluid dynamics.

#### In which disciplines is the concept of the centre of gravity most used?

Physics, mechanical engineering, and sports science.

#### Can the centre of gravity help in understanding the motion of a body?

Yes, especially in rotational dynamics.

#### Does the centroid have an impact on an object's motion?

Not directly, but it's important in design for balance.

#### Is the centre of gravity affected by the density of materials?

Yes, it varies with the distribution of mass.

#### Is the centroid relevant in 3D objects?

Yes, it's the center of mass for uniform density objects.

#### Does the centroid depend on the material of the object?

No, it's independent of the material.

#### In which areas is the concept of the centroid most applied?

Structural engineering, geometry, and art.

#### How does the centre of gravity influence vehicle design?

It affects stability, handling, and rollover risk.