摘要
有些物理量完全由它们的大小（用特定的单位）所决定，这类物理量的例子如呎，吋，加仑，美元等。另外一些其方向和大小都是重要的量，例如力和速度，称为向量。
Some physical quantities are completely determined when their magnitudes, in terms of specific units, are given. Examples of physical quantities of this kind are feet, inches, gallons, dollars, etc. Other quantities, such as forces and velocities, in which the direction as well as magnitude is important are called vector quantities.
