Overview
This lecture covers the fundamentals of scientific units, the importance of combining numbers with units, SI base units, prefixes, and derived units for measurement in science.
Importance of Units
- A number without a unit is incomplete; units provide context for measurement.
- Units clarify "of what" the quantity is and are essential for meaningful communication.
SI Fundamental Units
- The International System of Units (SI) defines seven base units; focus here is on three: meter (length), kilogram (mass), and second (time).
- 1 meter ≈ 1.094 yards, 1 kilogram ≈ 2.2 pounds, 1 minute = 60 seconds.
SI Prefixes and Meaning
- Prefixes adjust the size of base units for convenience (e.g., micro, milli, kilo).
- Large prefixes: kilo- (10³), mega- (10⁶), giga- (10⁹).
- Small prefixes: deci- (10⁻¹), centi- (10⁻²), milli- (10⁻³), micro- (10⁻⁶), nano- (10⁻⁹), pico- (10⁻¹²).
- Use of prefixes simplifies expressing very large or very small quantities.
Making and Converting Units with Prefixes
- A unit with a prefix equals a multiple or fraction of the base unit (1 km = 1,000 m, 1 ms = 0.001 s).
- Multiply the value by the prefix factor to convert to the base unit.
Derived Units
- Derived units result from multiplying or dividing base units (e.g., area, volume, velocity).
- Area: meter × meter = square meter (m²).
- Volume: meter × meter × meter = cubic meter (m³); 1 liter = 0.001 m³.
- 1 mL = 1 cm³ (cubic centimeter or cc); 1 L = 1,000 mL.
- Velocity: meters per second (m/s), can use other combinations like km/h.
Key Terms & Definitions
- SI (International System of Units) — globally accepted system of measurement.
- Base unit — fundamental unit defined by SI (e.g., meter, kilogram, second).
- Prefix — term attached to units to specify multiples or fractions (e.g., milli-, kilo-).
- Derived unit — unit formed by combining base units (e.g., m², m³, m/s).
- Per — indicates division in units (e.g., meters per second).
Action Items / Next Steps
- Learn the common SI prefixes and their factors.
- Practice converting between units with and without prefixes.
- Review fundamental and derived SI units.