Bottle Thermometer

Track how the sun changes the temperature in a room with a homemade thermometer.

  1. Ages: 5 - 16

  2. 30 minutes - 1 hour

  3. Messy

  4. Grownup needed


Materials you'll need

Step-by-step tutorial

  • Step 1

    Gather your materials.

    Photo reference of how to complete step 1

  • Step 2

    Fill the bottle a little more than halfway with rubbing alcohol. Then, drip a few drops of red food coloring into the bottle and swish it around until it’s well mixed.

    Photo reference of how to complete step 2

  • Step 3

    Pour a little bit of the alcohol out of the bottle and into the small cup. Set aside the cup.

    Photo reference of how to complete step 3

  • Step 4

    Cut the neck off of the balloon. Then, stretch the other end of the balloon over the top of the bottle and secure it with the rubber band.

    Photo reference of how to complete step 4

  • Step 5

    Cut a very small slit in the middle of the balloon. Then, insert the straw into the slit and gently push it into the bottle until just the tip of the straw is submerged in the alcohol.

    Photo reference of how to complete step 5

  • Step 6

    Use the pipette to drip the alcohol from the cup into the straw. The alcohol should stay in the straw. Keep adding alcohol until the alcohol level reaches about ⅓ of the way up the exposed part of the straw.

    Photo reference of how to complete step 6

  • Tip

    If the level in the straw doesn’t rise, you need to replace the balloon. Make a smaller slit in the new balloon.

  • Step 7

    Calibrate your thermometer! Place the bottle in a bowl of ice water and let it sit for about 5 minutes. Then, mark the level of the alcohol on the straw with a permanent marker.

    Photo reference of how to complete step 7

  • Factmagnifying icon graphic

    Calibrating is how you make sure a tool or instrument is measuring things correctly. You just check its measurements against something that you already know the measurement for!

  • Tip

    Take the temperature of the ice water with a food thermometer and record it. This will help you estimate temperatures when you’ve finished calibrating your thermometer!

  • Step 8

    Repeat step 7 with a bowl of hot water.

    Photo reference of how to complete step 8

  • Step 9

    Take the bottle out of the bowl and allow it to return to room temperature.

    Photo reference of how to complete step 9

  • Step 10

    Place your thermometer in a window that gets direct sunlight. Return to it throughout the day to see how the sun changes the temperature in the room!

    Photo reference of how to complete step 10

  • Factmagnifying icon graphic

    The first thermometer was made just like this by a guy named Daniel Fahrenheit back in 1714. Instead of using alcohol, though, he used mercury (that was before people realized that mercury is highly toxic, which is why your thermometer uses alcohol). Fahrenheit not only made the first thermometer — he also invented the scale for reading temperature with it. We still use that scale to this day, named after him. How many degrees Fahrenheit is the room you’re in right now?

  • Learn moremagnifying icon graphic

    Have you ever had trouble opening a door on a hot day? The high temperature makes some part of the door (the hinges, the door frame, or the door itself) expand, so it gets stuck. Things get bigger when their temperature increases and smaller when their temperature decreases. When folks first noticed this, it led to the creation of a handy tool for measuring temperature: the thermometer!

    The thermometer you made uses alcohol to read temperature. Alcohol changes its size when its temperature changes, even though you might not see it happen when the alcohol just sits in the bottle. The trick for making it noticeable is to put the alcohol in a thin tube, like a straw. With less space inside the straw, even a small change in the alcohol’s size makes a big difference to how high or low the top of the liquid is. 

    The alcohol always goes to the same level for the same temperature, so you can tell how hot or cold something is by comparing to different measurements of the alcohol level. 

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