Overview
This lecture covers the main temperature scales, how to convert between them, the concept of absolute zero, body temperature variations including hypothermia and hyperthermia, and applications of cryogenics, especially liquid nitrogen.
Temperature Scales and Conversions
- Temperature measures the average kinetic energy of a system.
- The three main temperature scales are Fahrenheit (°F), Celsius (°C), and Kelvin (K).
- Freezing point of water: 32°F, 0°C, 273 K; Boiling point: 212°F, 100°C, 373 K.
- Fahrenheit to Celsius: C = (F – 32) × 5/9.
- Celsius to Fahrenheit: F = (C × 9/5) + 32.
- Celsius to Kelvin: K = C + 273.15 (often rounded to 273).
Example Conversions
- 98.6°F = 37.0°C.
- 25.0°C = 77.0°F.
- 0°F = –17.8°C; 212°C = 414°F.
- Room temperature: 72.0°F = 22.2°C = 295 K.
Body Temperature and Health
- Normal body temperature: 98.6°F (±1.0°F).
- Fever: >100°F in adults; high fever: ≥104°F (seek medical attention).
- Hyperthermia: Body temp exceeds normal due to heat or medical conditions; symptoms include sweating and confusion.
- Hypothermia: Body temp below 95°F from cold exposure or illness; symptoms include shivering and sluggishness.
- Treat hyperthermia with hydration, cooling, and medication; treat hypothermia by warming and moving the individual.
Cryogenics and Liquid Nitrogen
- Cryogenics studies substances at –150°C to –273°C.
- Oxygen condenses to liquid at –183°C; liquid oxygen is used in medicine and aviation.
- Permanent gases like N₂, H₂, Cl₂, He can be liquefied by lowering temperature or increasing pressure.
- Absolute zero (0 K, –273°C) is the theoretical lowest temperature where particle motion is minimal.
- Liquid nitrogen boils at –196°C and is used in dermatology, fertility clinics, and culinary arts.
- Precautions with liquid nitrogen include protective gear and ventilation to avoid frostbite and asphyxiation.
Key Terms & Definitions
- Kinetic Energy — The energy of motion of particles in a substance.
- Fahrenheit Scale (°F) — Temperature scale used mainly in the U.S.; water freezes at 32°F, boils at 212°F.
- Celsius Scale (°C) — Scientific temperature scale; water freezes at 0°C, boils at 100°C.
- Kelvin Scale (K) — SI base temperature scale; 0 K is absolute zero.
- Absolute Zero — The lowest possible temperature (0 K, –273°C).
- Hyperthermia — Body temperature significantly above normal.
- Hypothermia — Body temperature significantly below normal.
- Cryogenics — Study of materials at extremely low temperatures.
Action Items / Next Steps
- Memorize temperature conversion equations for Fahrenheit, Celsius, and Kelvin.
- Complete problems #4, #7, and #10 in Section 2.E for more practice.