# Science Lesson Activities: How To Make A Thermometer

When you are teaching your children about thermometers and measuring temperature, the best way to teach them how a thermometer works is to make one and watch it in action. Use these simple instructions to build a homemade thermometer. Note that children should not do this project without adult supervision.

What you will need:

- A small clear plastic or glass bottle with a narrow opening at the neck

- A clear plastic straw

- Water

- Rubbing alcohol

- Food coloring

- Modeling clay

What to do:

1. Fill the bottle about halfway with rubbing alcohol.

2. Fill the remaining space in the bottle nearly to the top with water.

3. Add a few drops of food coloring to the water / alcohol mixture. Cover the top of the bottle and shake lightly to blend the coloring evenly.

4. Place the straw into the bottle.

5. Use the modeling clay to surround the straw at the opening of the bottle. Wedge the clay in so that it holds the stray in place and keeps the bottle closed, but does not squeeze the straw closed. Lift the straw up about ΒΌ of an inch, so it is not resting on the bottom of the bottle.

Your thermometer is ready. Place it in different locations that may be warmer or colder. Does the liquid rise in the straw when it is in the sunshine or when you place it in the refrigerator? Does holding the bottle in your hands change the level? Your hands are usually warmer than the room temperature.

To more closely monitor the level of the liquid, you can use a marker to put lines on the straw. Mark the level of the liquid at room temperature and when you put the thermometer in warm and cold locations. While your thermometer may not be as accurate as a commercial model, you should be able to easily see the effects of the temperature changes on it.

When liquid gets cold, it contracts and takes up less space. When the liquid in your thermometer gets warm, it expands and takes up more space. So, the liquid moves up through the straw when once it gets warmer. This is how thermometers work. Rubbing alcohol is more temperature sensitive than water, so it helps the thermometer show changes in temperature more quickly than using plain water. Commercial thermometers often use mercury because it reacts to temperature changes extremely quickly.

When you purchase a thermometer, it works in exactly the same way. The liquid inside it moves to show changes to the temperature and the markings along the thermometer indicate the temperature in one of the commonly used scales.

Temperature is usually measured in the Celsius or Fahrenheit scales, although some scientists use the Kelvin scale. In the Celsius scale, water freezes at 0 degrees and boils at 100 degrees. The Fahrenheit scale measures 32 degrees when water freezes and 212 degrees when water boils.

Do not place your homemade thermometer in the freezer or somewhere very hot since it is not designed for extreme temperatures. When you are finished with your experiment, please ensure an adult disposes of the pieces of the thermometer safely.