Overview
This lecture explains the SI system of measurement and scientific notation, focusing on unit conversions, prefixes, and how scientists handle large and small numbers.
The SI System and Base Units
- The SI (Système Internationale) system standardizes measurement for scientific communication.
- The SI system is based on the metric system, using units like meters and kilograms.
- There are seven SI base units: meter (length), kilogram (mass), second (time), ampere (electric current), candela (luminous intensity), mole (amount of substance), and kelvin (temperature).
- Derived units combine base units to measure things like speed (meters per second).
Converting Units
- The US uses the Imperial System (feet, inches, pounds), but American scientists use SI units.
- Conversion factors are multipliers used to change a measurement from one unit to another.
- Example: To convert 3 feet to inches, multiply by the conversion factor (12 in/1 ft) to get 36 inches.
- For metric to Imperial conversions, use multiple conversion factors and cancel out units step-by-step.
- Example: 24 centimeters × (1 inch/2.54 cm) × (1 foot/12 inches) = 0.79 feet.
Metric Prefixes and Decimal Movement
- Metric prefixes indicate multiples or fractions of units (e.g., kilo = 1000, milli = 1/1000).
- To convert within metric units, move the decimal point by the number of zeros in the prefix.
- The mnemonic "King Henry Died By Drinking Chocolate Milk" helps remember prefixes: kilo, hecto, deca, (base), deci, centi, milli.
Scientific Notation
- Scientific notation is used for expressing very large or very small numbers in a compact form.
- The format is a number (1 ≤ n < 10) multiplied by 10 raised to a power (e.g., 4.0 × 10¹³).
- Positive exponents are used for numbers greater than 1; negative exponents are for numbers less than 1.
- To convert to scientific notation, move the decimal to get a number between 1 and 10, counting the spaces for the exponent.
Key Terms & Definitions
- SI System — International system of units used for scientific measurements.
- Base Units — Fundamental units in the SI system (meter, kilogram, etc.).
- Derived Units — Units created by combining base units (e.g., meters/second).
- Conversion Factor — A ratio used to convert between units.
- Metric Prefix — Added to base units to indicate multiples or fractions (e.g., kilo-, milli-).
- Scientific Notation — Shorthand for large or small numbers as a number times a power of ten.
Action Items / Next Steps
- Review more practice problems, lab activities, and note-taking guides in the "Physics in Motion" toolkit.