Homemade Barometer

What You Need:

• 2-liter soda bottle, rinsed with label and lid removed
• Clear plastic cup
• Food coloring
• Black marker
• Water

What You Do:

1. Have your child pour a few inches of water into the plastic cup.
2. Have her choose a color she wants from the food coloring and drop a few drops into the water to change the color of the liquid.
3. She can now put the 2-liter bottle upside down in the cup. Make sure the mouth of the bottle is not touching the bottom of the cup, but is at least below the waterline.
4. Ask her to mark the water level on the side of the cup using a marker. She can also write the day or date next to the line to keep track of the waterline on specific days.
5. Have her check her barometer bottle when the weather changes. If the weather goes from rain to shine, the fluid in the plastic cup will fall and the fluid in the bottle will rise.

Helpful Tip: This is a great experiment to start on a rainy day, given that the liquid will have more movement as the weather clears.

What’s Going On?

When the toothpick points at high numbers, air pressure is pushing down on the balloon. When the toothpick points at lower numbers, there's less air pressure pushing on the balloon. Help your child recognize the connection between your barometer’s readings and the weather. On sunny, clear days the reading should be high. High pressure means the atmosphere is thicker over your area, and that usually means good weather. On stormy days, the reading should be lower because there's usually low pressure when it rains.