1.6
基本数量和派生数量
在任何单位制中，某些物理量的单位必须通过实际测量来指定。 这些测量值构成了系统的基本量，而它们的单位称为基本单位。 通过对这些基本量进行代数组合，我们可以得出所有其他物理量，这些物理量称为派生量，而对应的单位则称为派生单位。
国际标准化组织建议使用7个基本数量，这些基本数量构成了国际数量体系 (IS…
物理量可分为基本量和导出量。基本量可通过测量过程来表示，其单位称为基本单位。
例如，两点之间的距离以米为单位进行测量。此处的基本量是距离，用于测量它的单位是米，米是基本单位。
由基本量组合得到的物理量称为导出量，用于定义这些物理量的单位称为导出单位。
例如，汽车从一个地点到另一个地点的运动速度被定义为行驶距离除以行驶时间。这里，速度是由基本量距离和时间导出的导出量。
速度的单位是米每秒，该导出单位由基本单位米和秒导出。所有的导出量和导出单位分别由基本量和基本单位定义。
View the full transcript and gain access to JoVE Core videos
Q1: What is the difference between base quantities and derived quantities?
Base quantities are fundamental physical quantities measured directly through a measurement process, with units called base units—such as distance measured in meters. Derived quantities are obtained from algebraic combinations of base quantities, with units called derived units. For example, speed is a derived quantity calculated from distance divided by time, expressed in meters per second.
Q2: How many base quantities does the International System of Quantities recognize?
The International Organization for Standardization recommends seven base quantities, which form the International System of Quantities (ISQ). All other physical quantities can be expressed as combinations of these seven base physical quantities and their corresponding SI base units. This universal framework enables consistent measurement across all scientific disciplines.
Q3: What is an example of a derived unit in physics?
Meters per second is a derived unit used to measure speed, derived from the base units meters and seconds. Another example is square meters for area, calculated as the product of two lengths. Density provides a third example, expressed as kilograms per cubic meter (kg/m³), derived from mass divided by volume.
Q4: How are derived quantities formed from base quantities?
Derived quantities are formed through algebraic combinations of base quantities. For instance, area is derived by multiplying two length measurements, while density is derived by dividing mass by volume. These mathematical relationships between base quantities create new physical quantities with corresponding derived units.
Q5: Why is understanding base and derived units important for solving problems in physics?
Understanding base and derived units is essential for problem solving dimensional analysis, which verifies equation correctness and ensures unit consistency. Recognizing how derived units originate from base units helps students construct valid equations and convert between different measurement systems accurately.
Q6: Can all physical quantities be expressed using the seven SI base units?
Yes, all physical quantities can be derived from the seven base quantities, and the units of all physical quantities can be derived from the seven SI base units. This universal system allows any measurement in physics to be expressed as a combination of these fundamental units and quantities.
Q7: What role do base units play in units and standards of measurement?
Base units form the foundation of any measurement system and establish the units and standards of measurement for all physical quantities. Once base units are defined, all derived units are systematically constructed from them, creating a consistent and coherent framework for scientific measurement and communication.