48: Temperature- what is it?

We all know that winter is cold, but other than uncomfortable what actually is cold? And on that note what is the heat we feel on a hot summers day? What is temperature?

This week we’ll be going to the scientific basis of what temperature actually is, some of its extremes, how we measure it and finally how temperature can affect our bodies. At the end there is also some informational videos on what to do about hypothermia so I recommend watching those for a bit of first aid knowledge. Enjoy!

(Picture: Seattle Weather Blog)

Science of temperature

Digging down to the bare basics, what is temperature? What are the phenomena of hot and cold, other than uncomfortable if they get too extreme? Temperature is the kinetic energy of a substance, kinetic energy being the energy of motion. All substances are made up of atoms which are constantly moving, though on a level that is far too small for us to see. The more they are moving, the more energy they have and therefore the hotter they are. A very simple example of this is water. It is still when it is cool, but as is warms it starts to simmer (move a little) and then boil (move a lot).

Heat on the other hand is slightly different. It is the transfer of kinetic energy. The sun’s temperature is the kinetic energy that it holds within its atoms, whilst the heat of the sun is the warmth we feel from it- the kinetic energy being transferred to us.

In a cold substance such as ice atoms and molecules move slower than in a hot substance like gaseous water. (Image: University of Waikato)

Solid, liquid and gas

What does it mean then if atoms are moving faster or slower? One thing that is strongly affected is state. Atoms have bonds between, so in ice the bonds are very tight and strong making it a hard solid. When the atoms warms and start to have more kinetic energy, so move around more, they are pulling away from one another a little and the bonds holding them together become weaker. This allows the water to flow. It still is attracted to other water particles but these connections are weakened enough to allow us to easily separate them.

If we keep weakening these bonds with more kinetic energy they will be destroyed completely and so the substance won’t show any attraction to itself. This is gas. Different substances have different strengths of bonds within them, which is why the boiling and freezing points of water, oil and oxygen are all different. Even the things we commonly think of as solid, liquid or gas will change state at some point given a big enough change in kinetic energy. Rocks can and do melt when they are within the heat of volcanoes, and oxygen can become liquid or even solid and extremely low temperatures.

Raising temperatures not only changes the state but also the size of substances. As they have more kinetic energy and the atoms are moving around more, they need space to move and so the substances expands to account for this. This phenomenon was already observed by the Greek mathematician Hero in the first century AD, but it was astronomer Galileo in the early 1600s who first used this knowledge to create a thermometer.

If a substance expands at a known rate according to a set increase in temperature, this expansion can be used to calculate unknown temperatures. That is how modern thermometers work, with a set amount of mercury contained inside a glass tube of a specific size so that every time the temperature increases by one degree, the mercury expands and is pushed upwards the distance of one degree mark on the tube. Such basic principle yet to clever!

On the left: Liquid oxygen is a blueish colour (Picture: US Air Force/Public Domain). On the right: rock can become liquid when subjected to very high temperatures such as in a volcano (Picture: NPS/Public Domain)


Throughout the 1600s a variety of scientists came up with a variety of different thermometers, but things started to get a little confusing when everyone was measuring temperature according to different systems, meaning it was hard to compare anything. Today the international system of units is degrees Celsius, used by most of the world and used as a standard in science everywhere. Celsius measurements are based on the baseline that 00C is the point at which water freezes, and 1000C is the point at which it boils. In the United States however Fahrenheit is used to measure temperature. This was based on the idea that a solution of equal mixtures of salt, water and ice froze at 0 0F. This does not translate evenly to Celsius scale, but the freezing point of water in Fahrenheit is 320F (so 0 0C) and its boiling point 2120F (so 1000C).

The final unit of temperature measurement still widely used today, at least in physics. is Kelvin. 0 K is the lowest possible temperature, this being -2730C or -4590F. This is known as absolute zero, and is slightly theoretical. In experiments absolute zero can be approached but not actually achieved.

There were many different attempts at inventing thermometers using a variety of substances such as coloured water. Mercury is most commonly used today.

Highs and Lows

For a few general temperature facts- we already know the coldest possible temperature is absolute zero at -2730C (-4590F). A lot of these super cold temperatures were created in labs however. The coldest temperature measured outside at ground level on earth is -89.20C (-128.60F) in Vostok station Antarctica in 1983. Temperatures can get lower as the atmosphere thins, so the coldest measured temperature on earth was on an Antarctic ridge between Dome Argus and Dome Fuji at 3,900m high, this being -93.20C (-135.80F).

The hottest temperature on the other hand was measured in Death Valley, California in 1913, this being 56.70C (1340F). As for the hottest temperature in existence… well I don’t really know if that exists in the same way as absolute zero, but for some perspective the centre of the sun is thought to be around 15 million 0C (27million 0F) so, you know, it can get pretty hot.

What about humans and temperature? A normal healthy temperature for people is 36.5–37.5 °C (97.7–99.5 °F). When it is colder in the outside world, as for most of us it is pretty much year round, we compensate by behaviour such as wearing clothes, having heating etc… and by physiological processes in our body that preserve heat such as shivering. On the other hand if it is hotter, either due to outside temperatures or us heating up our body through movement like exercise we compensate by stripping off, having a cool drink and doing physiological things like sweating. However, whilst humans are impressively skilled at adapting to different temperatures compared to many other creatures, we do have our limits too.

When our body temperature drops, the kinetic energy in all of our cells and organs reduces. This can cause a person to slow down, have slurred speech and feel numb. As this starts to get more severe more function is lost, ice crystals can start to form in blood, people can start to get confused and disoriented as their brain function starts to go down, and eventually things like hypothermia and severe frostbite can lead to death. Amazingly hypothermia isn’t something which only occurs on Antarctic mountains. Hypothermia is classed as a body temperature below 35°C (95°F) and can easily happen in towns and cities on cool nights if people aren’t sufficiently warmly dressed, don’t have access to warmth and if they have been drinking alcohol as the physiological changes alcohol causes in the body can affect heat retention. Of course many milder cases of both hypothermia are completely curable with gentle warming of the body (never try to warm them up too quickly with e.g. hot water bottles even though that might seem like the obvious thing to do).

On the other end of the scale is hyperthermia (think of particles moving around so much they’re hyper). This is basically overheating, with body temperatures above 40°C (104°F) being potentially life threatening. Ten times more people actually die from hyperthermia and heat stroke each year rather than hypothermia.

However, as I said our bodies are incredibly good at being able to regulate our own temperatures, especially with our behaviours of what clothes we wear, the equipment we have to keep our homes warm from fires to underfloor heating, and having hot cups of tea or iced water if needed.

Our bodies and behaviour are pretty good at reacting to different outside temperatures to keep our internal temperature steady. (Picture: a popular meme with an unknown source)

Temperature is something we are aware of every day of our lives, and we often even unknowingly respond to it in our behaviour and our physiology. Hopefully this was an interesting little introduction then into what it actually is- dancing little atoms inside everything either doing a slow dance on a cool day or properly moving about when we feel it start to get hot.

For more info:

An article about the life of Daniel Gabriel Fahrenheit, who kicked off a lot of the early thermometer development in the 1600s: https://www.encyclopedia.com/people/history/historians-miscellaneous-biographies/daniel-gabriel-fahrenheit

A video about how to spot and react to hypothermia by the Canadian Red Cross:

What to do about hypothermia if you’re in the wild e.g. camping. This is practical first aid steps but of course call mountain rescue if you can as well:

Music: kongano.com

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