Hot and Cold

Hot and cold describe temperature and how warm or cool something is compared with a reference. An object is hot when its temperature is relatively high, while something cold has a relatively low temperature. Temperature is a physical quantity that tells us about the thermal state of matter, and it can be measured in degrees Celsius, degrees Fahrenheit, or kelvins.

A cup of freshly boiled water is much hotter than a glass of water taken from a refrigerator. The words hot and cold are also used for the weather, food, drinks, surfaces, and the human body. What feels hot or cold depends partly on the temperature of the object and partly on the conditions around it. Our skin detects changes in temperature, but the sensation of hot or cold is not always a precise measurement of temperature.

Heat and temperature are related but are not the same thing. Heat is energy transferred between objects because they have different temperatures, while temperature describes the thermal state of an object. When a hot object is placed next to a colder one, thermal energy generally flows from the warmer object to the cooler one until they approach the same temperature.

Materials can also change when their temperature changes: water can freeze into ice when sufficiently cooled and can become water vapour when heated enough. For young learners, everyday comparisons make the difference easy to notice: ice feels cold, while a warm drink feels hotter. Using a thermometer gives a more reliable measurement than touch alone. Hot and cold are therefore useful descriptions of temperature, but the exact temperature should be measured when precision is needed.