A property that can be quantitatively described, such as the volume of a sphere or the length of a vector.
可量化的值可以用数字形式描述出来的特性，例如球体的面积或者向量的长度
A vector quantity whose magnitude is a body's speed and whose direction is the body's direction of motion.
速度一种向量，其量值为物体的速率，其方向为物体运动的方向
