Suppose there is a plane now, and its X axis and Y axis have been determined. Now I want to create a number axis in space, which is perpendicular to both the X axis and the Y axis (that is, perpendicular to the existing plane).

Because the number axis has one direction, there can be two, but the number axis must have a positive direction, so one of the two must be chosen as the positive direction, so there is the right-handed rule.

The role of the right-hand rule

Hold out your right hand and open it. The four fingers first point in the X direction, and then naturally bend 90 degrees. If four fingers point in the direction of Y, then the thumb points in the positive direction of Z. ..

Or three axes are known, and now only Z is known, so which of the remaining two is X and which is Y can also be determined by the right-hand rule. The thumb points in the Z direction, and the four fingers naturally bend, pointing to X when unfolded, and pointing to Y after bending.

Extended data:

When defining the position of an object on a plane, that is, in two-dimensional space, use. And then what? Coordinate axis (called Cartesian coordinate or Cartesian coordinate). On the contrary, in space, that is, when defining a position for three dimensions, use? These three axes.

This is because the position on the plane is expressed by vertical and horizontal values, while the position in three-dimensional space is expressed by three coordinates on the basis of vertical and horizontal values plus "depth".

In three-dimensional coordinates, according to? The different directions of the axis (depth) are divided into two coordinate systems: right-handed system and left-handed system.

What is the direction of the important official (on the general two-dimensional rectangular coordinate system: to the right? Axis, up? Axis) From front to depth, the coordinate system is left-handed, and vice versa. The so-called right-handed system is a three-dimensional coordinate system represented by the following methods:

The thumb of the right hand represents the x axis.

The index finger represents the y axis.

The middle finger represents the z axis.

That is, with your thumb? Axis, index finger is? Axis, middle finger is? Axis should consider three-dimensional coordinates. If it is a right-handed subsystem, the middle finger points to your side. If you are left-handed, point your middle finger forward.

References:

Baidu encyclopedia-right-handed system