Units and Measurement Notes
1. What is a Unit?
When we measure something, we compare it to a standard called a unit. For example, saying “5 meters” means you’re comparing a length to the standard unit “meter”. There are two types of units:
- Fundamental/Base Units: Basic units for quantities like length, mass, and time. Examples: meter (m), kilogram (kg), second (s).
- Derived Units: Combinations of base units. Example: Speed = meters/second (m/s).
2. The International System of Units (SI)
SI is the globally accepted system. Earlier, countries used different systems:
| System | Length Unit | Mass Unit | Time Unit |
|---|---|---|---|
| CGS | Centimeter (cm) | Gram (g) | Second (s) |
| FPS | Foot (ft) | Pound (lb) | Second (s) |
| MKS | Meter (m) | Kilogram (kg) | Second (s) |
SI units were updated in 2018 to improve accuracy and consistency.
3. Key Terms
- Physical Quantity: Anything you can measure (e.g., length, temperature).
- System of Units: A collection of base and derived units (like SI).
Important Concepts for NEET
- SI units are the standard for scientific measurements worldwide.
- Know the base units: meter (length), kilogram (mass), second (time).
- Derived units are combinations of base units (e.g., m/s for speed).
- Differences between CGS, FPS, and MKS systems (see table above).
Tip: Practice converting units between systems (like meters to feet) – it’s a common exam question!
