Overview
This lecture introduces the SI base units, common conversion factors, and explains several derived units frequently used in physics and chemistry.
SI Base Units
- Length: meter (m)
- Mass: kilogram (kg)
- Time: second (s)
- Temperature: kelvin (K)
- Amount of substance: mole (mol)
- Electric current: ampere (A)
- Luminous intensity: candela (cd)
Common Conversion Factors
- 1 kilometer (km) = 1,000 meters (m)
- 1 meter = 100 centimeters (cm)
- 1 mile = 1.609 kilometers = 5,280 feet
- 1 yard = 3 feet; 1 foot = 12 inches; 1 inch = 2.54 cm
- 1 kilogram = 1,000 grams (g)
- 1 liter (L) = 1,000 milliliters (mL); 1 cubic centimeter (cm³) = 1 mL
- 1 cubic meter (m³) = 1,000 L
Units of Time
- 60 seconds = 1 minute; 60 minutes = 1 hour
- 24 hours = 1 day; 365 days = 1 year
Temperature Conversions
- K = °C + 273.15
- °F = 1.8 × °C + 32
Amount of Substance (Mole)
- 1 mole = 6.02 × 10²³ (Avogadro’s number)
Derived Units
- Velocity: meters per second (m/s)
- Acceleration: meters per second squared (m/s²)
- Force: newton (N) = kg·m/s²
- Area: square meters (m²)
- Volume: cubic meters (m³); chemistry often uses liters or mL
- Pressure: pascal (Pa) = N/m²; 1 atm = 101,300 Pa = 101.3 kPa = 760 torr = 760 mm Hg
- Density: kg/m³ (physics); g/cm³ or g/mL (chemistry)
- Work/Energy: joule (J) = N·m; calories and electron volts are also used
- Power: watt (W) = J/s; 1 horsepower = 746 W; 1 kilowatt (kW) = 1,000 W
- Momentum: kg·m/s or N·s
- Frequency: hertz (Hz) = 1/s
Electrical Concepts and Units
- Electric charge: coulomb (C)
- Electric current: ampere (A) = C/s
- Resistance: ohm (Ω) = V/A
- Electric potential/voltage: volt (V) = J/C
Key Terms & Definitions
- SI Unit — Standard unit set by the International System of Units.
- Derived Unit — Unit formed from combinations of base units (e.g., N, Pa).
- Mole — Quantity of 6.02 × 10²³ entities.
- Joule (J) — Unit of work/energy, equal to N·m.
- Pascal (Pa) — Unit of pressure, equal to N/m².
- Watt (W) — Unit of power, equal to J/s.
- Volt (V) — Unit of electric potential, equal to J/C.
- Coulomb (C) — Unit of electric charge.
Action Items / Next Steps
- Memorize SI base units and key derived units.
- Practice common unit conversions.
- Review formulas for derived physical quantities.
- Be able to distinguish between similar units (e.g., power vs. energy).