Make a Thermometer

A thermometer is an instrument that measures the temperature. Temperature is measured in a scale called Fahrenheit (in the United States) and in Celsius or Centigrade (in many other countries). The point where water freezes is 32 degrees Fahrenheit (F for short) and 0 degrees Celsius (C). The point where water boils is 212 degrees F and 100 degrees C. If you want to know how to convert from F to C or from C to F, see the end of this page.

Some scientific thermometers use the Kelvin scale, where 0 degrees Kelvin is called absolute zero -- a place where there is no movement of any parts of matter, where substances have no thermal energy. It's about minus 273.15 degrees C (below 0o C) or 459.67 degrees below 0oF. Scientists have never been able to measure anything at absolute, absolute zero.

Thermometers help us know what the weather will be like. If it will be 90oF outside, we're not going to put on a winter coat. Or if it's below zero, we won't be wearing shorts. Here's a way to show how a simple thermometer works.

List of Materials:

• Tap water
• Rubbing alcohol (do not drink!)
• Clear, narrow-necked plastic bottle (11-ounce water bottles work well)
• Food coloring
• Clear plastic drinking straw
• Modeling clay
What to Do:
• Pour equal parts of tap water and rubbing alcohol into the bottle filling about 1/8 to a 1/4 of the bottle.
• Add a couple of drops of food coloring and mix.
• Put the straw in the bottle, (DO NOT DRINK MIXTURE) but don't let the straw touch the bottom.
• Use the modeling clay to seal the neck of the bottle, so the straw stays in place.
• Now hold your hands on the bottle and watch what happens to the mixture in the bottle.
Results:

Congratulations!!! You just made a thermometer. Just like any thermometer, the mixture expanded when it was warmed. This made the liquid no longer fit in the bottom of the bottle. As the alcohol expanded the colored mixture moved up through the straw. If the bottle were to get very hot, the liquid would have come through the top of the straw.

You can watch your thermometer and see how the liquid changes throughout the day. What happens if your thermometer is in shadow or in sunlight? What happens when it gets colder? How does wind affect the thermometer?

Of course, in order to accurately read the temperature, you will need to buy a real thermometer that is carefully calibrated for temperature changes. This one is to see how a thermometer works -- just for fun.

After you're done with your thermometer, dispose of the liquid properly and rinse the bottle well. Cut it in half, or have a parent cut it in half, so the bottle can't be reused. Then recycle the plastic. The used bottle could have some left over alcohol in it, and you don't want anyone to reuse the bottle for drinking water. So, it's best to recycle the bottle.

Changing Temperature Scales:

The Fahrenheit scale was named after Gabriel D. Fahrenheit who lived from 1686 to 1736. He devised a way of measuring temperature. The Celsius scale was named after Anders Celsius, its inventor, who lived from 1701-1744. The Celsius scale is also called Centigrade. The Centi in centigrade means 100 and is used by scientists. It is the temperature scale used by most of the world. The difference between the temperature where water freezes and boils is an even number of degrees...100. In the Fahrenheit scale, the difference between freezing (32oF) and boiling (212oF) is 180.

You can change the temperature in Fahrenheit into Celsius using math.

Take your number; subtract 32o from it; and divide the remainder by 1.8.
Example

Change 75 degrees Fahrenheit into Celsius.

75 - 32 = 43
43 / 1.8 = 23.88oC
So, 75oF is equal to 23.88oC

To change the temperature in Celsius to Fahrenheit: Multiply your number by 1.8 and add 32o.

Example:

Change 12 degrees Celsius into Fahrenheit.

12 x 1.8 = 21.6
21.6 + 32 = 53.6oF

So, 12oC is equal to 53.6oF

This page taken from Energy Quest, written by the California Energy Commission at http://www.energy.ca.gov/education/projects/projects-html/thermometer.html

Note: The water level in the straw changes not because the water expands (it does a tiny amount), but because the air above the water expands and contracts. As the air expands it pushes on the water in the bottle. The water has nowhere to go but up the straw. If your thermometer isn't working it could be because your clay seal isn't airtight. If the clay seal is not airtight, the air will expand and leak out the top instead of pushing on the water.

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