Temperature Scales Overview

Overview

This lecture covers the concept of temperature, how it's measured, and the differences between Fahrenheit, Celsius, and Kelvin temperature scales.

Temperature measures the random motion (kinetic energy) of the particles in a substance.
High temperature means particles move faster; low temperature means particles move slower.
The everyday sense of "hot" or "cold" is related to these particle motions.

The commonly used temperature unit in the US is Fahrenheit, but it's not ideal for scientific purposes.
Fahrenheit was originally based on human body temperature, which varies between people and times of day.
Celsius is a better scientific scale, based on water freezing at 0°C and boiling at 100°C.
Water's boiling point changes with air pressure, so Celsius is still not perfect for universal accuracy.

Kelvin is the scientific standard and is based on absolute zero, where all particle motion stops.
Absolute zero is the lowest possible temperature for any substance and is the same everywhere.
Kelvin is an absolute scale, unlike Fahrenheit and Celsius, which are relative.
There are no negative temperatures in Kelvin; 0 K is the coldest possible temperature.
Kelvin temperatures are indicated without the word "degree" (e.g., 300 K, not 300°K).

Fahrenheit and Celsius depend on reference points that can change (body temperature, water's boiling point).
Kelvin's reference point (absolute zero) does not change, making it the most reliable and precise.

Temperature — Measurement of the average kinetic energy (motion) of particles in a substance.
Fahrenheit — A temperature scale originally based on human body temperature; commonly used in the US.
Celsius — A temperature scale based on the freezing (0°C) and boiling (100°C) points of water.
Kelvin — An absolute temperature scale starting at absolute zero, used in science.
Absolute zero — The lowest possible temperature (0 K), where all particle motion stops.
Relative scale — A measurement system based on changeable reference points (like Fahrenheit or Celsius).
Absolute scale — A measurement system based on a fixed, unchanging reference (like Kelvin).

Know the differences between Fahrenheit, Celsius, and Kelvin temperature scales.
Remember Kelvin uses no "degree" symbol and starts at absolute zero.
Review why Kelvin is favored for scientific temperature measurements.