The exceedingly hot weather we have been experiencing was unusual for late spring.  There have been heat advisories and excessive heat warnings in effect across much of the Eastern interior of the United States, followed by a weekend of record smashing heat in the country’s Southwest.  

Severe heat waves have begun to affect people in other parts of the globe with frightening regularity.  Experts tell us that the heat waves of the past two decades are not good predictors of the risks that will confront us in the decades to come. There is a definite link between greenhouse gas emissions and sweltering temperatures and today’s most extreme heat waves could not have happened centuries ago.  That is, before humans started to warm up the planet.  According to recent New York Times article, heat is climate change at its most devastatingly intimate, ravaging not just landscapes and ecosystems and infrastructure, but the depths of individual human bodies.

What Is Heat?

All of today’s discussion about  the hot weather sparked my interest in heat and temperatures, and I ended up by reading about thermodynamics.  

Thermodynamics is defined as the branch of physical science that deals with the relations between heat and other forms of energy (such as mechanical, electrical, or chemical energy), and, by extension, of the relationships between all forms of energy.  The heat of an object is the total energy of all the molecular motion inside that object. Temperature is the measure of the thermal energy or average heat of the molecules in a substance.

Hotness And Temperature

We all recognize temperature as a measure of “hotness” at a given point within the system. This leaves this intensive property with no numerical magnitude. Furthermore, our sense of this property may be misleading. A metal chair, for instance, will feel much colder than a wooden one even when both are at the same temperature.

Fortunately, several properties of materials change with temperature in a repeatable way, and this forms the basis for an accurate temperature measurement. The commonly used mercury-in-glass thermometer, for example, is based on the expansion of mercury with temperature. Temperature is also measured by using several other temperature-dependent properties.

It is common experience that a cup of hot coffee left on the table eventually cools off and a cold drink eventually warms up. That is, when a body is brought into contact with another body which is at a different temperature, heat is transferred from the body which is at a higher temperature to that at a lower one, until both bodies attain the same temperature. At this point, the heat transfer terminates, and the two bodies are said to have reached a state of thermal equilibrium. The equality of temperature is the only requirement for thermal equilibrium.

Temperature describes the internal energy of a system, whereas heat refers to the energy transferred between two objects at different temperatures.

Everything in this universe is in motion, and motion begets kinetic energy. The faster a particle is moving, the more kinetic energy it has. In fact, kinetic energy increases exponentially with particle velocity.

Where does temperature fit into all of this? Well, temperature is simply an average measure of the kinetic energy for particles of matter. Another way of putting it would be that temperature simply describes the average vibration of particles.

There are various scales used to describe temperature. In the United States, the most commonly used unit for temperature is Fahrenheit, while much of the rest of the world uses Celsius (or Centigrade). Physicists often prefer to measure temperature in Kelvin, which is also the standard international unit for temperature.

For the Kelvin scale, zero refers to the absolute minimum temperature that matter can have, whereas in the Celsius scale, zero degrees is the temperature at which water freezes at a pressure of one atmosphere (273.15 Kelvin). At 100 degrees Celsius, water begins to boil at a pressure of one atmosphere, offering a neat, linear and relatable scale for describing temperature. The German instrument maker Daniel Fahrenheit (1686-1736) was the first to use mercury in a thermometer: He set 0° at the lowest temperature he could reach with a mixture of salt, ice, and water, and for 100° he chose his body temperature, a readily transportable but unreliable standard. On this scale water freezes at 32°F and boils at 212°F.


Hero, a Greek philosopher and mathematician, is credited with the idea for the first thermometer, writing in the 1st century CE about the relationship between temperature and the expansion of air in his work Pneumatics.

Global Warming

According to the United Nations as greenhouse gas emissions including carbon dioxide, methane, soot and other pollutants  blanket the Earth, they trap the sun’s heat. This leads to global warming and climate change. The world is now warming faster than at any point in recorded history. Climate experts project that the world will experience at least 5.7 degrees Fahrenheit by 2100 and should global emissions continue on their current path this small rise will have grave consequences.

Max Sherman is a medical writer and pharmacist retired from the medical device industry.  His new book “Science Snippets” is available from Amazon and other book sellers. It contains a number of previously published columns.  He can be reached by email at