What's the temperature outside where you live?
You might have a thermometer at home - one that measures the temperature in units called Fahrenheit degrees.
A long time ago, humans didn't have a way to talk specifically about how cold or hot it was. Over time, scientists began to discover that they could measure changes in temperature using various methods (including one using glass bulbs of different substances that floated or sank depending on the temperature!).
But a reliable scale wasn't discovered until the 1700s when a man name Daniel Fahrenheit came along. He used mercury in thermometers, which is more reliable than alcohol or water (even though it's more dangerous). He created the scale of associated numbers that we still use today!
Want to make your own thermometer and pretend to be like those before Fahrenheit scales came along? In this month's 20 Minute Lab, we'll do just that with (safe!) materials you have around the house!
If your thermometer doesn't move, or you see the water rising but then suddenly fall, it may be because the Play-doh is not completely sealed around the straw. If the seal isn't tight, the lost pressure in the jar can cause the experiment to fail.
What made the colored water in your straw go up or down? Well, when you put your jar into the hot water dish, it heated up the liquid in your jar.
Molecules in hot water have a lot of energy - they bounce around and spread out, which increases the volume. The water actually expanded, but because of the tight seal around the lid, there was nowhere for it to go but up the straw!
When you moved your jar to the cold water bowl, the water molecules in the jar slowed down a lot. They move closer together (as though they were huddling together for warmth!), decreasing the volume and causing the liquid in the straw to lower.
Thermometers that you buy at the store use alcohol (or mercury) because it has a low freezing point. While water freezes at 32° F, alcohol doesn't freeze until -173° F! (Mercury doesn't freeze until -37.9° F) That's how thermometers can measure the temperature outside even when it's below freezing!
On a thermometer, the level of liquid can be 'read' by looking at the printed lines with numbers next to it, telling you the temperature.
Mercury was considered better because it was very reliable in its expansion and so could be counted on to show the exact temperature that matched the Fahrenheit scale. Today though, digital or metal-based thermometers are preferred because if they break, they don't spill mercury everywhere, which is a toxic material.
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