ベクトル表記のデカルト形式

The moment of force is calculated as the cross-product of position and force vectors expressed in Cartesian form. A determinant is constructed using the position vector components and force vector components with unit vectors. Expanding this determinant yields the Cartesian vector formulation of the moment, which indicates both magnitude and rotational direction about a specific axis.

Unit vectors i, j, and k form the first row of the determinant used to express the cross-product in Cartesian form. They define the x, y, and z directions respectively. The position and force vector components fill the remaining rows, allowing the determinant expansion to produce moment components in each coordinate direction.

The force is applied perpendicular to the y-z plane, meaning it acts only along the x-direction. Therefore, the y and z components of the force vector are zero, while only the x-component equals 10 N. This simplifies the determinant calculation and reveals that the moment acts exclusively about the z-axis.

A positive moment value indicates counterclockwise rotation when viewed from the positive direction of the axis. In the revolving door example, the positive 40 N·m moment about the z-axis means the door rotates counterclockwise. The sign convention helps determine both magnitude and sense of rotation in three-dimensional space.

The determinant method is the mathematical tool for computing moment of a force about an axis vector. By arranging position and force components in determinant form and expanding, you obtain the vector components of the moment. This approach directly produces the moment vector, which specifies both rotational magnitude and axis orientation.

The Cartesian vector formulation expresses the moment as components along the x, y, and z axes, revealing how the moment distributes in three-dimensional space. Each component indicates the rotational effect about its respective axis. This detailed breakdown is essential for analyzing complex force systems and understanding resultant moment vector formulation.

Use Cartesian form when forces act in three dimensions or when you need complete moment vector information including direction and all components. Scalar formulation works for planar problems with perpendicular forces and distances. Cartesian form provides comprehensive results for complex spatial configurations and is necessary for moment of a force scalar formulation comparisons.