Overview
This lecture covers temperature unit conversions among Celsius, Fahrenheit, and Kelvin, and explains the differences between potential and kinetic energy, including unit conversions for energy.
Temperature Units and Conversions
- Fahrenheit (°F) is commonly used in daily life, Celsius (°C) in labs, and Kelvin (K) is the SI unit for temperature.
- To convert °C to °F: °F = (°C × 9/5) + 32.
- To convert °F to °C: °C = (°F − 32) × 5/9.
- To convert °C to K: K = °C + 273 (more precisely, K = °C + 273.15).
- Example: 25°C × 9/5 + 32 = 77°F.
- Example: (65.3°F − 32) × 5/9 = 18.5°C.
- Example: 18.5°C + 273 = 291 K.
Energy: Types and Examples
- Kinetic energy is energy due to motion (e.g., a car moving, an earthquake).
- Potential energy is stored energy due to position or chemical bonds (e.g., energy in food, a wound spring).
- Kinetic: car speeding, earthquake shaking.
- Potential: energy in food, wound spring.
Energy Units and Conversions
- Common energy units: calories (cal), kilocalories (kcal), joules (J), kilojoules (kJ).
- 1 kcal = 1,000 cal.
- 1 cal = 4.184 J.
- 1 kJ = 1,000 J.
- To convert 750 kcal to J: 750 × 1,000 × 4.184 = 3,100,000 J (to two significant figures).
- To convert to kJ: 3,100,000 J ÷ 1,000 = 3.1 × 10³ kJ.
Key Terms & Definitions
- Fahrenheit (°F) — Temperature scale used in the US; freezing point of water is 32°F.
- Celsius (°C) — Metric temperature scale; freezing point of water is 0°C.
- Kelvin (K) — SI unit for temperature; absolute zero is 0 K.
- Potential Energy — Stored energy based on position or chemical bonds.
- Kinetic Energy — Energy of objects in motion.
- Joule (J) — SI unit of energy.
- Calorie (cal) — Energy unit; 1 cal = 4.184 J.
- Kilocalorie (kcal) — 1 kcal = 1,000 cal.
Action Items / Next Steps
- Practice temperature and energy unit conversions.
- Review textbook examples 3.18, 3.24, and 3.28.
- Remember significant figures in calculations.