The First BIG Question

The BIG Question: What is temperature and how do we measure it?

Words to use when explaining this include:

• phases of matter, solid, liquid, and gas
• molecular motion
• Celsius
• Fahrenheit
• freezing point
• boiling point
• liquid thermometer
• phase changes

Optional questions to answer for a higher grade:
1. How is plasma different from solids, liquids, and gases?
2. What are the lowest and highest temperatures ever measured on Earth?
3. What are the freezing and boiling points of substances other than water?
4. How do digital and liquid crystal thermometers work?
5. What is the Kelvin temperature scale and who uses it?

Sample Response

Temperature is a measure of how fast molecules are moving. We measure it using tools called thermometers. One type of thermometer is a liquid thermometer. In a common type of liquid thermometer there is some red colored alcohol in a narrow glass tube. When the alcohol gets warmer it expands and takes up more room so the level of alcohol goes up in the tube. Two of the common scales used for measuring temperature are the Celsius and the Fahrenheit scales. Most of the rest of the world uses just the Celsius scale so that is the one scientists use all the time. That makes it easier and more accurate for us to compare data with other scientists. On the Celsius scale, at sea level, pure water boils at 100 degrees and it freezes at zero degrees. On the Fahrenheit scale, at sea level, pure water boils at 212 degrees and freezes at 32 degrees. An important thing to know about temperature is that it takes a lot of energy to change matter from one phase to another. For example, when water is in the solid state of ice it has only a little molecular motion, but if you add a lot of energy the water molecules move faster and it melts into ice. Then the temperature goes up quickly until you get to the point where the water is boiling. Then the temperature levels off again because all the heat energy is going into the phase change that makes the liquid water turn in to water vapor or a gas.


I was curious if there was any point where the Fahrenheit and the Celsius scales are the same. I looked on a website called “The Straight Dope: Fighting Ignorance since 1973 (it’s taking longer than we thought” and it said that negative forty degrees Celsius is the same as negative forty degrees Fahrenheit. Wow, I hope it doesn’t get that cold this winter.