TEMPERATURE | Detailed Explanation

Temperature in our lives:

What is more relaxing than stepping into a warm shower or bath on a chilly day? But if the water is too hot or too cold, you may feel discomfort and spend as little time bathing as possible. What makes taking a shower or bath a pleasant experience instead of a shock? Of course, it is the temperature of the water.

The temperature of the air outside is also an everyday concern. Knowing the temperature helps us to decide how to dress and how to plan our day. Since knowledge of the temperature is so useful, public buildings often display it along with the time. Yet, depending on where you live, the number displayed may reflect entirely different conditions. Why, for example, would a reading of 40 degrees in the United States call for wearing a coat, whereas a 40-degree reading in Europe call for the lightest possible clothing?

WHAT IS TEMPERATURE?

Temperature is a measure of hotness and coldness. But what makes a substance hot or cold? If you could peer into the molecular and atomic structure of materials as they heat up, you would see various changes taking place. Consider a pan of water as heat is applied to it on a stove.

The water molecules move faster and faster. Soon the water boils. This occurs when the water molecules are moving so fast that they bounce off one another and no longer stick together in liquid form. The water is actually beginning to change into  a gas, which we see as steam. Bubbles of gas form first at the bottom of the pan, since the temperature there is the highest. Even though heat is continually added during this transformation of water into steam, the temperature does not change. This is because it takes energy to break the molecules free from the liquid state and transfer them to the gaseous state. The added heat supplies that energy. So instead of making the water hotter, it simply causes more water molecules to change to the gaseous state.

The water molecules in the gaseous state move faster and faster, vibrating and shifting position with temperature increases. If the temperature of the steam was raised extremely high, say into the tens or hundreds of millions of degrees, even the electrons would be stripped off the atoms. At such high temperatures, the nuclei, the tiny cores at the center of atoms, would strike one another so hard that nuclear reactions could take place. In fact, this is the idea behind the goal of using nuclear fusion to generate power.

Temperature Scales

Very simply, where the Fahrenheit scale is used, such as in the United States, 40 degrees is cold, not far above the freezing point of water. But in Europe where the Celsius scale is commonly used, 40 degrees registers a temperature that is very hot. In this article we will only consider these two scales used by the general public. 

Where did the Fahrenheit and the Celsius temperature scales come from?

In 1714 Gabriel Daniel Fahrenheit, a German physicist, used a mercury thermometer to devise a temperature scale. He determined three fixed points. He wanted the zero point on his scale to be as low as possible. So he mixed ice, water, and a kind of salt, and the temperature of the mixture dropped down to the lowest point he could then obtain. That temperature became 0 degrees on his scale. After that, Fahrenheit selected the temperature of a healthy human body as the upper point on his scale.He set this temperature at 96 degrees. (However, since then the body temperature of a healthy human has been found to be about 2 1/2 degrees higher than what he arbitrarily set.) To obtain the third fixed point, he measured the freezing point of water and found it to be 32 degrees. Later, the scale was applied to the boiling point of water. The temperature turned out to be 212 degrees at sea level, which Fahrenheit later proposed as the upper point on his scale.

A contemporary of Gabriel Fahrenheit was Anders Celsius, a Swedish astronomer, who lived from 1701 to 1744. In 1742 Celsius devised a temperature scale that is also identified by it's inventor's name. The scale is based on two fixed points; 0 degrees is the freezing point of water, and 100 degrees is the boiling point of water at sea level. Since Celsius divided his thermometer into 100 equal parts, it is also known as the centigrade temperature scale. The Celsius scale is used wherever metric units have become accepted.

From Fahrenheit to Celsius

Since both the Fahrenheit and Celsius scales are in common use today, it is often necessary to convert from one to the other. How is this done? Well, note that the difference between the boiling point and the freezing point of water on the Fahrenheit scale is 180 degrees (212 degrees minus 32 degrees). But on the Celsius scale, it is 100 degrees. Therefore, the ratio between the two scales is 180/100, or 9/5.

Thus, to change from Fahrenheit to Celsius, first subtract 32 from the Fahrenheit temperature. Then multiply the difference by 5/9. As an example, say the Fahrenheit temperature is a sweltering 104 degrees. To arrive at the Celsius temperature, subtract 32 from 104, which gives 72. Then multiply 72 by 5/9. The result is 40, which is the Celsius temperature. Indeed, 40 degrees Celsius is sweltering!

On the other hand, to change from Celsius to Fahrenheit, you need to multiply the degrees Celsius by 9/5 and then afterward add 32. So, as an example, say the temperature is 20 degrees Celsius. What does that equal on the Fahrenheit scale? Multiplying 20 by 9/5, you get 36. By adding 32 to 36, you arrive at the Fahrenheit temperature of 68 degrees.

Temperature Ranges.

As far as is known, temperature does not have an upper limit. On the other hand, it does seem to have a lower limit. Absolute zero has been set at -459.67 degrees Fahrenheit, or -273.15 degrees Celsius. This is the point at which molecules and atoms of a substance have the least possible energy.

The surface of the planet Pluto has an estimated temperature of about -350 degrees Fahrenheit, or -210 degrees Celsius. In 1965 astronomers learned that the blackness of outer space has a temperature of about -455 degrees Fahrenheit, or -270 degrees Celsius, just 3 degrees above absolute zero on the Celsius scale. Toward the other extreme, the center of the sun is believed to be about 15 million degrees Celsius. But stars larger that the sun-and there are stars thousands of times larger-probably have much higher temperatures.

What about temperature ranges here on earth? They fluctuate in a relatively narrow range. In America a temperature of -128.6 degrees Fahrenheit, or -89.2 degrees Celsius, was measures on July 21, 1983. And a record high temperature of 136 degrees Fahrenheit, or 58 degrees Celsius, was registered at El Aziza,
Tripolitania, in Northern Africa on September 13 1922. But the vast majority of humans have not experienced temperatures even approaching those extremes.

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