Overview
This lecture covers the fundamental concepts of temperature, the three main temperature scales (Fahrenheit, Celsius, Kelvin), and how to convert between them.
Temperature Concepts
- Temperature measures the average kinetic energy (energy of motion) in a system.
- The unit "degrees" is used for Fahrenheit and Celsius, while Kelvin is simply "K" (no degrees).
Fahrenheit Scale (°F)
- Used primarily in the United States.
- Water freezes at 32°F and boils at 212°F.
Celsius Scale (°C)
- Used in science and most of the world.
- Water freezes at 0°C and boils at 100°C.
- The scale is divided into 100 equal parts between freezing and boiling points.
Kelvin Scale (K)
- SI unit for temperature, used in scientific contexts, especially gas laws.
- Kelvin units are the same size as Celsius degrees but shifted by 273.15.
- Zero Kelvin (0 K) is absolute zero, the lowest possible temperature.
Temperature Conversions
- Fahrenheit to Celsius: °C = (°F − 32) × (5/9)
- Celsius to Fahrenheit: °F = (°C × 9/5) + 32
- Celsius to Kelvin: K = °C + 273.15
- Kelvin to Celsius: °C = K − 273.15
- For most classwork, 273 can be used instead of 273.15 for conversions.
Conversion Examples
- Normal body temperature: 98.6°F = 37.0°C (to three significant figures)
- 25°C = 77.0°F
- Room temperature 72.0°F = 22.2°C = 295 K (rounded to three significant figures)
Key Terms & Definitions
- Absolute Zero — The lowest possible temperature (0 K or −273.15°C), where no kinetic energy remains.
- Kelvin (K) — The SI base unit for temperature, starting at absolute zero.
- Celsius (°C) — A temperature scale based on water’s freezing (0°C) and boiling (100°C) points.
- Fahrenheit (°F) — A temperature scale commonly used in the US; water freezes at 32°F and boils at 212°F.
Action Items / Next Steps
- Practice converting temperatures between Fahrenheit, Celsius, and Kelvin.
- Memorize freezing and boiling points of water in all three scales.
- Be prepared to convert Celsius to Kelvin quickly for scientific applications.