✔ Sistema Internacional de Unidades SI

How Are Physical Quantities Measured?

Introduction to Physical Quantities

• Physical quantities express the laws of physics, including length, time, force, density, temperature, luminous intensity, and magnetic intensity.

• Historically, measurements were inconsistent; for example, grass was measured by the waist size of a king. This led to discrepancies when different kings had varying body types.

Standardization of Measurements

• The need for uniform measurements across the globe prompted the establishment of standards.

• The General Conference on Weights and Measures (CGPM), initiated in 1889, established seven basic units that form the basis of the International System of Units (SI).

Basic Units in SI

• The seven basic SI units include:

• Time: seconds

• Length: meters

• Mass: kilograms

• Amount of substance: moles

• Temperature: Kelvin (thermodynamic)

• Electric current: amperes

• Luminous intensity: candelas

Use of Prefixes for Simplification

• To simplify notation for very large or small quantities in SI units, prefixes were recommended during CGPM meetings from 1960 to 1975.

• For instance, 10^18 can be represented as "exa" followed by the unit. An example is one million bytes being expressed as 10^12 bytes or one terabyte (TB).

Competing Measurement Systems

• Besides SI units, two other major systems exist:

• Gaussian system (not covered extensively in this context)

• British system still used daily in the USA.

Importance of Learning SI Units

• Understanding SI units is crucial for precise measurements that can be verified and communicated effectively between laboratories.

• The use of prefixes aids in simplifying results and understanding global measurement standards.