Overview
This lecture covers the SI system of measurement and scientific notation, explaining how these systems help scientists communicate measurements and handle very large or small numbers.
SI System and Metric Units
- The SI System (Systeme Internationale) is a global measurement standard used by scientists for consistent communication.
- The metric system is the basis of SI, using units like meters (length) and kilograms (mass).
- SI was first published in 1960 and uses 7 base units: meter, kilogram, second, ampere, candela, mole, and kelvin.
- Derived units are created by combining base units (e.g., meters per second for speed).
- The United States uses the Imperial system for daily life but scientists use SI units for research.
Conversion between Units
- Conversion factors are multipliers that convert a quantity from one unit to another.
- To convert between Imperial units (e.g., feet to inches), multiply by a conversion factor (e.g., 12 inches/1 foot).
- To convert between metric and Imperial, use known conversion factors (e.g., 1 inch = 2.54 cm).
- Multiple conversion steps may be needed; cancel units as you go to ensure correct result.
- Metric-to-metric conversions can be done by moving the decimal point, according to the number of zeros in the prefix.
Metric Prefixes and Decimals
- Metric prefixes represent powers of ten (e.g., kilo = 1,000, milli = 0.001).
- Common prefixes: kilo (k), hecto (h), deca (da), base unit (meter/liter/gram), deci (d), centi (c), milli (m).
- The mnemonic "King Henry Died By Drinking Chocolate Milk" helps remember the order of metric prefixes.
Scientific Notation
- Scientific notation expresses very large or small numbers as a product of a number (1–10) and a power of ten.
- Format: a × 10ⁿ, where a is at least 1 but less than 10, and n is an integer.
- Positive exponents indicate large numbers (e.g., 4 × 10¹³), negative exponents indicate small numbers (e.g., 5.4 × 10⁻⁵).
- To convert a number into scientific notation, move the decimal point to form a number ≥1 and <10, counting decimal places for the exponent.
Key Terms & Definitions
- SI System — An international standard for measurements based on the metric system.
- Base Unit — One of the seven fundamental units in the SI system.
- Derived Unit — A unit formed by combining base units.
- Conversion Factor — A ratio used to convert one unit to another.
- Metric Prefix — A prefix representing a specific power of ten.
- Scientific Notation — A shorthand way to write very large or small numbers using powers of ten.
Action Items / Next Steps
- Review Derived Units in your Unit 1 Toolkit.
- Practice conversions and scientific notation using the "Physics in Motion" toolkit.