Homemade Thermometer

What You Need:

  • Modeling clay
  • Red food coloring
  • Water
  • Clear straw
  • Rubbing alcohol
  • 11 ounce narrow-neck, clear plastic bottle
  • Thermometer (optional)

What You Do:

  1. Pour equal amounts of tap water and rubbing alcohol into the bottle until it's a quarter full.
  2. Add a few drops of red food coloring, and shake the bottle to mix it.
  3. Insert the straw into the bottle, not letting it sink to the bottom.
  4. Wrap modeling clay around part of the straw and the opening of the bottle to make it stay. Let part of the straw stick out of the bottle. The clay should be tight around the straw and cover the bottle mouth, but make sure to leave the top opening of the straw uncovered.
  5. Test the thermometer! Have your child put her hands around the bottle. What happens to the mixture when her warm hands are on it?

You can also put the thermometer outside and see how the contraption reacts to the hot or cold temperature. Or, place the thermomter in a bowl of hot water and then put it immediately in the freezer. What happens?

What's Going On?

When the alcohol and water mixture gets hot, the mixture expands, sending the water up the straw. How hot would it have to be for the water to come out of the straw?

Challenge your child to make a scale for the thermometer. Ask your child to use a store bought thermometer to identify the temperature that the area where the homemade thermometer mixture is. Put a line on the straw where the liquid is, and mark the temperature that the thermometer says. Do this in various cold and hot places in the house.

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