Overview
This lecture covers the scientific definition of temperature, the distinction between heat and temperature, and details on Fahrenheit, Celsius, and Kelvin temperature scales, including how to convert between them.
Definition of Temperature & Kinetic Energy
- Temperature is defined as the average kinetic energy of a group of particles.
- Kinetic energy is the energy of motion, calculated as ½ × mass (kg) × velocity² (m/s)².
- For an object to have temperature, its particles must have mass and be in motion.
Importance of 'Average' in Temperature
- "Average" means not all particles have the same kinetic energy; their energies form a bell curve distribution.
- Some particles in a liquid may have enough energy to evaporate even at temperatures below boiling point.
Difference Between Heat and Temperature
- Heat is the energy that flows from objects at higher temperature to those at lower temperature.
- Heat is a quantity measured in joules (J), while temperature is an average value.
- A small hot object may be at a higher temperature but contain less heat than a large, cooler object.
Temperature Scales: Fahrenheit, Celsius, and Kelvin
- Fahrenheit: Water freezes at 32°F, boils at 212°F, with 180° between; units used in everyday U.S. life.
- Celsius: Water freezes at 0°C, boils at 100°C, with 100° between; based on water properties.
- Celsius degrees are larger than Fahrenheit degrees; 1°C = 1.8°F.
- Conversion formulas:
- °C = (°F − 32) × 5⁄9 or °C = (°F − 32) / 1.8
- °F = (°C × 9⁄5) + 32 or °F = (°C × 1.8) + 32
- K = °C + 273.15 °C = K − 273.15
Kelvin Scale & Absolute Zero
- Kelvin scale sets zero at absolute zero, where molecular motion stops (0 K).
- Kelvin and Celsius scales have units of equal size; only the zero point differs.
- Kelvin does not use the term "degrees;" say "100 K" not "100 degrees Kelvin."
- Kelvin is the only temperature scale suitable for use in scientific laws due to its absolute zero.
Example: Temperature Conversion and Significant Figures
- When converting temperatures, your answer must have the same number of decimal places as the original value.
- Example: 93.2 K − 273.15 = -179.9 °C
Key Terms & Definitions
- Temperature — Average kinetic energy of a group of particles.
- Kinetic Energy — Energy of motion; ½ × mass × velocity².
- Heat — Energy transfer due to temperature difference, measured in joules.
- Absolute Zero — Lowest possible temperature, 0 K, where particle motion stops.
- Kelvin — Absolute temperature scale where 0 K = absolute zero.
Action Items / Next Steps
- Memorize temperature conversion formulas between Fahrenheit, Celsius, and Kelvin.
- Practice converting temperatures and paying attention to significant figures in answers.
- Read "Fahrenheit 451" by Ray Bradbury for cultural context (as suggested in lecture).