7th grade science project ideas


Science Fair Project: Yes You Can Actually Make Your Own Thermometer

You can be a hero to your friends and family because you never have to go out in the cold again without being properly dressed after you have done this project and have your own thermometer.

The bulb thermometer is the common glass thermometer. Most are made with a fluid called mercury.

Bulb thermometers are based on the principle that a liquid changes its volume relative to its temperature. Liquids take up less space when they are cold and more space when they are warm.

You may have noticed that liquids like water, milk and cooking oil all take up more or less space as their temperatures change. In these cases, the change in volume is fairly small. All bulb thermometers use a fairly large bulb and a narrow tube to accentuate the change in volume. You can see this for yourself by making your own bulb thermometer.

For your science fair project you will need certain materials including two glass jars. Obtain jars with water tight lids. The lids may be plastic or metal and the screw on type will serve you best. You will also need a large nail, hammer, silly putty, two straws, marking pen, water and a thermometer.

To do this science fair project for eighth grade or any other grade you must punch a hole somewhere near the middle of the lid of the jars. You may use a drill if you wish or you may use the hammer and nail. The hole should be about the same size as the diameter of the straw.

Insert the end of the straw into the hole, and then seal around the hole with silly putty both on the inside and the outside of the lid. If you are not using silly putty, you may use plumber's putty or caulk or chewing gum. Fill jars with cold water. You can do this either by filling it with water and leaving it in the refrigerator overnight, or by making some ice water in a pitcher and then pouring the ice water into your jar. No ice in the jar please.

You may add some food coloring if you desire and shake it up.

You want the jar filled to the brim with cold water, as full as you can get it without overflowing.

Put the lid on the jar. When you screw on the cap, a little water may spill out the sides, and a little water may be visible in the straw. That's okay. Place the jar in your kitchen sink, plug the sink and run hot water into the sink until the sink is about half full. Watch the level of the liquid in the straw. You will see the water in the jar expanding. As the water in the jar gets warmer, it will expand and rise up the straw.

You have created a simple bulb thermometer. With an appropriate marker, mark the temperature on the straw. Use a real thermometer for reference the first time, then after that you will be able to use your home made thermometer to tell temperature.

Using water in your thermometer is somewhat limiting. You will not be able to go below freezing at 32 degrees F or above boiling at 212 degrees (0 to 100C), which is the boiling point. This limitation should not really present a problem because if you are experimenting with your thermometer at home, it is not very likely that temperatures will go as low as freezing or as high as boiling. Because the "bulb" (the jar) is so large, it takes a long time for the thermometer to reach the same temperatures as the object it is measuring -- perhaps an hour or more. Because the top of the tube is open, the water can evaporate and pick up dust and debris. Sealing mercury in a small glass thermometer solves these problems. The small size of the bulb means that the bulb reaches the temperature of what it is measuring very quickly, and the tube in such a thermometer is micro-fine. Mercury also avoids the freezing and boiling problems associated with water. The reason we are using water in this experiment instead of mercury is for ease of handling.

To make this project more interesting, we suggest that you make two or more different thermometers using the instructions above. Use your imagination. Use any size jar, and different straws or tubes and then, calibrate the new thermometer and check to see which one is the most accurate. For your science fair project, you may wish to test two or three home made thermometers in the sun, in the house, or in partial sunlight to see which gives you the best results.

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