Temperature: what it is, types, how it is measured and importance

The definition of temperature indicates that it is a physical quantity that reflects the amount of internal energy present in a body or in the environment. This energy manifests itself as heat when it is high, or as cold when it is low. In more precise terms, temperature is linked to the kinetic energy of the particles that make up matter, that is, with the movement they perform when moving, rotating or vibrating. The greater the kinetic energy of those particles, the hotter the system is perceived, which means its temperature is higher.

Discover the Difference between heat and temperature.

Here we present the different types of temperatures:

• Ambient or air temperature: predominates in the environment that surrounds us. It is measured to know the climate or thermal conditions of a place.
• Body temperature: is the temperature that maintains a living being within an adequate range for its vital functions to occur normally.
• Surface temperature: the temperature of the surface of an object, without considering its interior. For example, the surface of a metal in the sun.
• Internal or core temperature: indicates the heat inside a body or system, such as the interior of the Earth or the core of an organism.
• Absolute temperature: it is measured in Kelvin (K) and starts from absolute zero, where the movement of particles ceases. It is the scale used in physics and chemistry for scientific calculations.

In the International System of Units (SI), the unit used is the kelvin (K), associated with the Kelvin scale or absolute scale, where the value of 0 K represents absolute zero, that is, the point at which all molecular movement ceases. A kelvin has the same magnitude as a degree Celsius, which means that the temperature increases are equivalent on both scales, although they start from different references. Outside of the scientific field, the most used scales are Celsius, also known as Centigrade, and, to a lesser extent, Fahrenheit, which continues to be in common use mainly in the United States. Below we can analyze each scale in greater detail:

• Celsius scale (°C): also called centigrade, it takes as reference points the freezing point of water (0 °C) and its boiling point (100 °C), under normal atmospheric pressure. It is the most used scale in daily life and in most countries in the world.
• Kelvin scale (K): mainly used in the scientific field, it starts from absolute zero (0 K), the theoretical temperature at which the movement of particles ceases. It does not use the degree symbol (°) and each increment of 1 K is equivalent to an increment of 1 °C.
• Fahrenheit Scale (°F): It is the most used scale in the United States and some Caribbean countries. Set the freezing point of water at 32°F and the boiling point at 212°F, under the same pressure conditions.

In addition to these, there are other less common scales, such as the Rankine scale or the Réaumur scale, used historically or in specific contexts.

There are different instruments designed to measure temperature, each with different operating principles and levels of precision. The most common are:

• Liquid-in-glass thermometer: uses the expansion of a liquid (usually mercury or colored alcohol) within a sealed glass capillary tube. As the temperature increases, the liquid expands and moves up the graduated scale.
• Gas thermometer: it is based on the variation in pressure or volume of a gas when the temperature changes. It is very precise and is used as a reference in laboratories.
• Digital thermometer: works through electronic sensors that convert thermal energy into electrical signals. It is fast, safe and commonly used in domestic and medical settings.
• Resistance Thermometer (RTD): Measures temperature from changes in the electrical resistance of a conductive material (such as platinum). It is used in industrial and scientific measurements.
• Thermistor: electronic device whose resistance varies with temperature. It is sensitive and can detect small thermal changes, which is why it is used in precision equipment.
• Thermocouple: consists of two different metals joined at their ends, which generate an electrical potential difference when exposed to different temperatures. It is widely used in ovens, engines and industrial processes.
• Pyrometer: measures temperature from a distance, detecting the thermal radiation emitted by a hot body. It is used in metallurgy, industrial furnaces and volcanology.
• Infrared thermometer: similar to the pyrometer, it captures infrared radiation to measure temperature without direct contact, being common in medical and environmental applications.

The temperature of a place or a body is not constant, but can vary depending on different physical and environmental factors. Among the most important are:

• Latitude: determines the amount of solar radiation that an area receives. Regions near the equator are warmer, while areas near the poles have lower temperatures.
• Altitude: As the height above sea level increases, the temperature decreases, as the air becomes less dense and retains less heat. The temperature decreases approximately 0.6 to 1 °C every 100 meters.
• Time of day and season of the year: during the day temperatures are usually higher due to direct sunlight, while at night they drop. In addition, the seasons are influenced by the inclination of the Earth’s axis: summer is warmer and winter is colder. A curious fact is that in mountainous areas or in cities located in valleys, cloudy nights can maintain warmer temperatures, since they delay the loss of heat accumulated during the day. On the other hand, in the early hours of the morning the phenomenon of thermal inversion may occur, in which cold air is trapped in the lower layers and warm air remains above, reversing the normal distribution of temperature.
• Proximity to the sea: water has a high capacity to store and release heat, which mitigates extreme temperature variations. Furthermore, the interaction between the sea and the atmosphere, especially through sea breezes, contributes to moderating the climate: summers are cooler and winters are milder.
• Ocean currents: Warm currents (such as the Gulf current) raise the temperature of the regions they pass through, while cold currents (such as the Humboldt current) reduce it.
• Vegetation cover and type of surface: Vegetation influences temperature through shade and transpiration, which cool the environment and moderate thermal variations. Forests and green areas maintain milder and more constant temperatures. On the contrary, urban or desert surfaces, with little vegetation and materials that absorb heat (asphalt, cement or bare rock), accumulate thermal energy during the day and release it quickly at night, causing greater temperature fluctuations and contributing to the urban heat island phenomenon.
• Atmospheric pressure and air masses: changes in air pressure and the movement of warm or cold air masses also influence local thermal variations.

• Maintains the health and survival of living beings: humans and animals need to maintain their body temperature within specific ranges for physiological processes to function properly; Very high or very low temperatures can cause heat stroke, hypothermia and thermal stress. Extreme temperatures can exacerbate certain diseases, such as cardiovascular or respiratory diseases. Likewise, temperature can affect the reproduction and survival of species. For example, in some reptile species such as turtles, environmental temperature determines the sex of the offspring. Extreme changes can alter the ratio of males to females, affecting the survival of the population.
• Agriculture and plant production: plants require appropriate temperature ranges to grow and flower. In fruit trees, for example, it is essential that the necessary hours of cold are accumulated for flowering and fruiting to occur correctly. Without this control, productivity is reduced and the harvest may be compromised.
• Preservation of food and medicines: Many foods need cold storage to avoid bacteria and preserve their freshness. Medications and vaccines must be kept within controlled ranges to preserve their effectiveness.
• Industrial and technological processes: in industry, temperature control is crucial in chemical, metallurgical or electronic processes, since variations can affect quality, safety and efficiency. In technology, electronic devices require cooling systems to prevent overheating and failure.
• Climate and environment: monitoring temperature helps predict climate phenomena, plan agriculture and manage natural resources. In urban life, maintaining moderate temperatures in buildings and cities improves quality of life and reduces energy consumption.

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