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Overview
Temperature is a measure of how hot or cold a system is, but in physics it has a deeper meaning. It is connected to the microscopic motion of particles and determines the direction of heat transfer. When two systems are placed in thermal contact, energy tends to transfer from the higher-temperature system to the lower-temperature system until thermal equilibrium is reached.
Thermal Condition
Temperature describes the thermal state of matter. It helps predict whether energy will transfer as heat between systems and whether a system is hotter or colder relative to another system.
Particle Motion
In many materials, temperature is related to the average kinetic energy of particles. Higher temperature generally means particles are moving, vibrating, or rotating more energetically.
Thermal Equilibrium
Thermal equilibrium occurs when systems in contact no longer exchange net heat because they have the same temperature. Temperature is the quantity that determines whether this equilibrium has been reached.
Temperature Scales
Common temperature scales include Celsius, Fahrenheit, and Kelvin. Kelvin is the SI temperature scale and is especially important in scientific equations.
Absolute Zero
Absolute zero is the lowest theoretical temperature, corresponding to zero kelvin. It represents the lower limit of thermal energy in classical intuition, though quantum physics gives a more complete description.
Temperature vs. Heat
Temperature is not the same as heat. Temperature describes thermal condition, while heat is energy transferred because of a temperature difference.
Measuring Temperature
Thermometers measure temperature by using physical changes that depend on thermal state, such as expansion, electrical resistance, radiation, or pressure.
Common Mistakes
A common mistake is treating temperature as the amount of heat in an object. A large cool object can contain more internal thermal energy than a small hot object.
Why This Matters in Physics
Temperature is foundational for heat transfer, thermal energy, phase changes, gas laws, thermodynamics, engines, climate, materials, and many biological and technological systems.