Weather is a big part of our lives and affects our day-to-day plans. To help our children understand the weather, let’s learn how to make a thermometer. We’ll also look at the science behind HOW a DIY thermometer works.
What Is Needed to Make a Thermometer
You just need a few household materials (an empty water bottle, water, rubbing alcohol, tape, a straw) to make a thermometer with your kids and show them the science behind how a thermometer works. Afterall, weather conditions can determine what we wear, what we do, and where we go. If it is cold and snowing outside, we will probably not put on flip-flops and work in the garden. If it rains, the baseball game will probably get canceled.
What Is Weather?
Scientifically speaking, the weather is the atmospheric conditions in a place within a relatively short amount of time. These conditions might change hour-by-hour or minute-by-minute. It might be cloudy, cold, and rainy in the morning and hot and sunny by the afternoon.
Temperature, precipitation, cloud cover, wind, barometric pressure, and humidity are all atmospheric conditions that we can measure to describe and predict the weather.
Make a Thermometer – What is Temperature?
Before we make a thermometer with our kids or students, let’s talk about temperature; it is how hot or cold something is measured by a thermometer. Air temperature is probably the first weather condition you check each day. The temperature will determine if you wear a coat or not, or maybe if you go outside at all! The temperature affects if and how many people do their daily activities.
The atmosphere’s temperature, or air, is determined by the sunlight present. The more sunlight reaches the Earth, the higher the temperature. When rays of sunlight hit the Earth, the Earth warms up, which in turn warms the atmosphere.
Heat can build up over time, which is one of the reasons why the shorter days of winter are colder than the longer days of summer.
The temperature of the Earth’s atmosphere is also determined by the angle at which the sunlight hits the Earth.
No matter the season – summer, winter, spring, or fall – the same sun with the same amount of brightness shines on the Earth. If the sunlight is just as bright at all times of the year, why are the temperatures so different?
The temperatures on Earth are lower in winter due to the tilt of the Earth’s axis and its orbit around the Sun. The Earth’s axis is tilted at an angle of about 23.5 degrees relative to its orbital plane. This tilt causes different parts of the Earth to receive varying amounts of sunlight throughout the year.
The sun is directly overhead in the summer, and its rays directly hit the Earth. In the winter months, the sun sits lower on the horizon. Sunlight arrives at a shallower angle, resulting in the same amount of solar energy being spread over a larger area. This leads to less heating and lower temperatures.
Instructions – How to Make a Thermometer
This was one of our favorite weather activities to do. If it’s a hot day, the thermometer starts out reading cooler inside because of the air conditioning. But when it’s placed outside, it’s fun to watch the temperature rise and mark it on the bottle and index card. If it’s cold outside, the opposite will happen.
You can also make the temperature rise and fall by placing the bottle in hot water and cold water. We opted to put the thermometer in the freezer, then took it out in the sun on a 50-degree day.
Let your children try different variations—ice water, hot water, outside in the sun, outside in the shade, in the freezer—so they can test their ideas.
- Fill the water bottle a little past halfway with equal parts of rubbing alcohol and room temperature water. You can also use ½ cup of each. (We wanted to see the mixture rise above the bottle, so we filled it slightly past halfway.)
- Add a few drops of food coloring and mix it up.
- Place the straw in the bottle and pack the playdough around the top. Ensure the straw stands straight and there is an airtight "seal." The bottom of the straw should NOT touch the bottom of the bottle.
- Tape an index card to the back of the straw. Your children can mark where the water mixture level is as the thermometer begins to read warm enough to move past the seal.
- Place the thermometer outside in a sunny place. If it's very cold outside, then you can place the thermometer in hot water, then in cold water to watch the temperature rise and fall.
- Place the thermometer in the freezer for a few minutes and look at the level of the water-alcohol mixture. Then, take it out and place at room temperature. What happens? How quickly did the liquid move?
- Take it further! What happens when you place this mixture in the freezer? Does it freeze completely? (Hint: Rubbing alcohol only freezes at temperatures below 128 degrees Fahrenheit.)
How the DIY Thermometer Works
As the Sun heats the water mixture in the bottle, the space between the molecules expand. Warmer mixture is less dense than when the mixture is colder. This causes the air pressure in the bottle to rise, so the mixture needs somewhere to go. The mixture moves up the straw.
When the temperature of the bottle cools, the space between the molecules shrinks, so the water becomes more dense. This causes the water in the straw to move down. This process is called convection. (If you do not have a tight seal with the clay, the mixture will not move up the straw. As the molecules warm and the pressure builds, the air can escape through the leak around the neck of the bottle.) You can learn more about convection currents in this activity.
If you’d like to study more about the properties of water, check out our post on testing the properties of water.