What is temperature?

Leon thinks it is very hot today. He is just lying down and eating ice cream! Lina would rather have a cup of hot tea, she feels quite cold. We use words such as “hot” “warm” “chilly”, “cold” everyday when we talk about things like the weather, food and drinks. But people do not always feel the same and might disagree whether a day is warm or cold.

Is there a way to tell how hot or cold something is, so that everyone understands? Yes, we can MEASURE it using a device called thermometer. Thermometers indicate precisely how hot or how cold the measured substance is. This measure is called TEMPERATURE. But why is the tea hot and the ice cream cold?

Why do temperatures of different objects vary? To answer this question, we need to look much, much deeper. Everything around us is made of tiny particles - atoms and molecules - which constantly move. All these moving particles carry energy related to motion - KINETIC ENERGY. Their motion is random - they all move at different speeds and in different directions.

This is why we measure their AVERAGE KINETIC ENERGY - and that’s temperature! The temperature of hot tea is high because the particles inside it move fast. Their average kinetic energy is high. It’s the opposite in ice cream. The temperature of ice cream is low because the particles move much slower and they have low kinetic energy.

In theory, if the temperature is low enough, the particles will stop moving completely. Their kinetic energy will be equal to zero. This is as cold as anything can get. This is called the ABSOLUTE ZERO POINT. To make sure the measurement of temperature is precise and means the same to everyone, we need scales that people have agreed on.

The absolute zero point is the lowest point of one of such scales - Kelvin scale. Temperature values on the Kelvin scale start at absolute zero and can never be negative. Kelvin scale is an ABSOLUTE SCALE. You might have not heard of Kelvin scale because it’s mostly used in science. In everyday life, we use either CELSIUS SCALE or FAHRENHEIT SCALE.

CELSIUS scale has two characteristic points - the temperature at which water freezes, and the temperature at which water boils. The difference between these two points is divided by one hundred. Each of the resulting equal parts is called a degree. FAHRENHEIT scale is used commonly in the United States and a few other countries. On the Fahrenheit scale, the freezing point of water is 32 degrees and the boiling point is 212 degrees.

Both of these scales are related to boiling and freezing of water. They are RELATIVE scales. Using these scales you can measure the temperature precisely, but how you perceive it is relative. It depends on what the temperature of your body is. If something has a higher temperature than your body, you perceive it as warm or hot.

If its temperature is much lower, you will perceive it as cold. Our normal body temperature is about 37 degrees Celsius or 98 degrees Fahrenheit. So maybe if Lina feels cold on a hot day, her body temperature is higher than normal? Oh, no, Lina, you have a fever! It seems you are sick again!