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How to Make a Homemade Thermometer

Learn how to make a homemade thermometer with the instructions in this Howcast science project video.


Hey guys. Right now it's wintertime.

Generally this is the time when you, me, your teachers, your parents we get sick. You get the flu, you get colds, you get a stomach virus. Usually when you're sick mommies and daddies always do one thing first. They put something in your mouth and it's known as a thermometer. But the reality is you don't always have to buy a thermometer. You can actually make one. Think about it. Most people have thermometers in their homes too. Your car has one, your homes have one. I'm going to show you how to make a homemade thermometer that will actually rise and drop according to the temperature of your house.

What do I need? A plastic bottle. I love science that requires things that you have in your home. First what I'm going to do is take this plastic bottle and fill it up a quarter of the way with an equal portion of water and rubbing alcohol. First I'll start with the water. I'm going to make an equal amount of water and an equal amount of rubbing alcohol. Please be very careful if you're using rubbing alcohol. Ask your parents for supervision and for some help. I'm going to pour the rubbing alcohol so that I have an equal portion.

Now I'm going to take the two liquids, you cannot tell which is which, and I'm going to drop it in my bottle like this and like this. Now I'm going to add some food coloring because when Mommy puts the thermometer in your mouth if it's not the electric ones there's usually a red line, right? You see the red line rise and drop. Why does it rise and drop? Because when this mixture is heated it expands, it actually takes up more space. When you have a fever you are more hot. So what happens is the red mixture in the thermometer is being heated and as it expands it's telling your mom ‛My child’s got a fever.’

Will this homemade thermometer work? Watch this. I'm going to add a couple drops of red food coloring and I'm just going to stir it around. Now I'm going to take my straw. The key is not to have the straw hit the bottom of the bottle. You want it to be in the liquid but not down touching the base, a little bit above. I'm going to use clay to seal the top. Ready? Take it, drop it. It can not hit the bottom. So what I'm going to do is take the clay and I'm going to seal the top so that no air can get in and no air can get out. All of a sudden I'm going to make sure the straw is in the liquid but not touching the bottom. Just like that. Now let's test my thermometer and see if it works.

Usually if you have a fever are you hotter or colder? You're hotter. So what I'm going to do is take hot water. If you think the water is too warm, be safe and use a paper towel. Pour the hot water into a pitcher or something big enough that your homemade thermometer can fit in. Pour it.

Now this has a lot of heat energy and guess what? When I drop my homemade thermometer into this hot, hot water the heat will be transferred into the liquid. The mixture inside is going to expand and watch what happens to my thermometer.

It starts to rise. It's already happening. As you take your thermometer and you put it into the hot water the heat from the water is going to travel into your mixture. As it gets heated it's going to expand and inside the straw the water will rise and rise and rise and fortunately like what happens to you when you have a fever, you just made a homemade thermometer.

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