Easy
30 min
There’s no more obvious a change in temperature as there is when Fall becomes Winter. You see it in the frost on your windows, and you hear it in the requests to “turn the thermostat up!”
It got us thinking about the old-school thermometers - the ones with mercury in them that hung near the window to tell us what the temperature was outside. Does anyone still own one of those?
For this Waypoint, we’re taking those memories and getting some household items together to make our own thermometer. The kids will learn a thing or two about how they work and the whole family will finally have an answer to whose room is the warmest.
Add equal parts water and rubbing alcohol to your plastic bottle, so the combined solution fills a third of the bottle. If your kids are doing this step, consider using protective eyewear or gloves. Be cautious of the alcohol.
Rubbing alcohol has a freezing point much lower than water, so by using an alcohol solution, we’ll be able to measure temperatures much lower than the freezing point of water (32℉).
Fun side note: German scientist, Daniel Gabriel Fahrenheit, is widely credited with inventing the alcohol thermometer in 1709 in part due to his glassblowing skills.
With water and rubbing alcohol being clear and all, it won’t be easy to see the liquid as it moves up and down.
To help everyone see it better, add a few drops of the red food coloring to your solution. This can get messy. Probably best for a parent to do this step.
Adding red color to an alcohol thermometer has always been a common practice. If you come across one with silver coloring, you have your hands on a mercury thermometer.
To create a gauge out of our straw, slide the straw into the opening of the bottle, so it’s submerged in the solution and hangs just above the bottom of the bottle.
Now take your modeling clay, and wrap it around the sides of the straw where it enters the bottle. Mold it around the bottle opening and the straw to secure it in place. Little fingers are great at this. Make sure not to pinch the straw or cover the top of it.
The clay molding needs to be secure enough that no air can enter the bottle. To test out your seal, mix a little more of the alcohol and red dye together, then carefully drip it down the straw.
If the added alcohol stays within the straw, congratulations! Your seal is secure. If the alcohol blends together with the rest of the solution, air is getting in somewhere. Mold the clay some more, and continue dripping in drops of alcohol until it stays within the straw.
Once you know it’s secure, you’re ready to measure! Use a marker to mark the bottle at the point in which the red appears in the straw. This is your room temperature reading against which all others will be measured. Now time to explore!
If you’re like us, and you’re doing this in December, the best way to try it on hot is to place it closer to a fireplace OR place your thermometer in a bowl and add hot water.
The red alcohol solution will rise up in the straw. That’s because all three states of matter (solid, liquid and gas) expand when heated. The atoms themselves don’t expand, but the volume they take up does, because the atoms are vibrating faster within the solution. How cool is that?
Once you see the thermometer go up, it’s time to see it go down. You can make this happen by exposing it to cooler temperatures. We took ours outside where the temperature was in the 30s, so the solution in our straw shot down fast below the surface.
The solution will contract and move down the straw when cooled, because the molecules in the solution are moving slower and drawing them closer to each other.
If you live in a state that’s always warm, you can try this out in your refrigerator or freezer. Matter of fact, take the thermometer around to different spots in the house, warm it up with your hands, cool it down by rubbing ice around it. See how quickly you can get it to go up and down.
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