# What are heat and cold?

Temperature changes cause the state of matter to change. But what exactly is temperature?

Temperature changes cause the state of matter to change. But what exactly is temperature?

#### What is heat and cold?

Heat is caused by atoms and molecules in motion. The faster the particles move, the more often they bump into each other and transfer kinetic energy to each other and the material heats up.

As the temperature increases, the state of matter changes from a solid state, when it is the coldest, to an electric gas, when it becomes the hottest.

#### The state of matter can be in four ways:

1 – Solid form applies to the coldest state, where the atoms in eg metals or molecules are packed tightly together.

2 – In liquids, like water, the molecules float around each other.

3 – In gases , such as water vapour, the molecules move freely around each other and collide more often than in liquids.

4 – In an electric gas, the atomic nuclei and electrons are separated and move freely around each other. Electric gas has an electric charge because it contains positive atomic nuclei and negative electrons.

#### What is called alcohol?

The lowest possible temperature is called alkal. With alcohol, all substances are in a state where the atoms are completely stationary and do not possess any kinetic energy.

The atoms nevertheless have at their disposal a small amount of quantum energy, but for example both the atomic nuclei and the electrons spin inside the atoms. Physicists therefore describe alcohol as the lowest energy state, where the atoms simply cannot get any colder.

On the Celsius scale, alcohol is at -273.15, which corresponds to zero degrees on the Kelvin scale.

#### What is the difference between the different temperature scales?

The Kelvin scale starts at zero and the degrees increase at the same intervals as on the Celsius scale.

The Celsius scale is the most widely used temperature scale in the world. A scientist named Anders Celsius prepared the scale in 1742. Celcius based the scale on the melting and boiling points of water. Originally, the boiling point of water was fixed at 0° C. In 1744, however, the scale was reversed so that 0 degrees corresponded to the melting point of water and 100 degrees to its boiling point. This was thought to be more logical as the degrees rise in line with higher temperatures.

The Fahrenheit scale is the official temperature scale in the United States. German physicist Daniel Gabriel Fahrenheit developed the temperature scale named after him.

On the original scale, Fahrenheit set zero as the lowest temperature to which he could cool a salt solution, while 100° F corresponded to human body temperature. On the modern scale, the freezing point is at 32° F, while the southern point of water is at 212° F.

### How is the Earth’s temperature measured?

Global temperature measurements originated from measuring stations on land and aboard ships sailing across the high seas. By 1880, it had been possible to measure the temperature widely enough to determine the average annual temperature of the earth.

Today, a dense network of weather stations can be found on all continents, as well as on the high seas. The measuring station network is not evenly distributed over the entire globe, and it can be noted that there are far more measuring stations in Europe than in the Sahara, for example.

Scientists have divided the earth’s surface into squares, each square measuring five by five degrees. For each field, the average temperature measured in all weather stations is calculated. Finally, the average of all the fields is calculated, and this is how the scientists obtain the average temperature of the entire earth.