What is the Difference Between Center of Gravity and Center of Mass?

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The center of gravity and the center of mass are two related concepts in physics, but they have distinct differences:

  • Center of Mass: This is the point at which the distribution of mass is equal in all directions. It is the location where the entire mass of the body is directed. The center of mass does not depend on the gravitational field and is calculated as the integral of mass density.
  • Center of Gravity: This is the point at which the distribution of weight is equal in all directions. It does depend on the gravitational field, as it is calculated as the integral of force of gravity. When the gravitational field (g) changes, the center of gravity's value also changes.

In most situations in physics, the center of mass and the center of gravity are interchangeable concepts, as the gravitational field is usually assumed to be constant. However, in cases where the gravitational field is not uniform, such as when considering very tall objects or situations with varying gravitational fields, the two concepts may differ.

Comparative Table: Center of Gravity vs Center of Mass

The difference between the center of gravity and the center of mass lies in the factors they are based on. Here is a table summarizing their differences:

Feature Center of Mass Center of Gravity
Definition The center of mass is the point at which the entire mass of the body is concentrated, and it is calculated based on the body's mass. The center of gravity is the point at which the body's entire weight is suspended, and it is calculated based on the body's weight.
Distribution There is a uniform distribution of mass in the body. There is a uniform distribution of the weight of the body.
Calculation The center of mass is the weighted average of location with respect to mass. The center of gravity is the weighted average of location with respect to mass times the local gravitational field.
Gravitational Field The center of mass is based on the mass of the body and is independent of the gravitational field. The center of gravity is based on the weight of the body and is affected by the gravitational field.

In most situations pertaining to physics, the center of mass and the center of gravity are interchangeable concepts, mainly because the gravitational field is assumed to be constant. However, they might have different values when the gravitational field is not uniform.