Materials Needed:
A bottle with a narrow neck
Vinegar
Baking soda
Funnel or straw
Water
Balloon
 
Step by step

1. Pour about an inch of liquid--half vinegar, half water--into the bottle.

2. Use the funnel to fill the ballon half full of baking soda. (If you don't have a funnel, you can use a straw to load the balloon. Stick the straw into the baking soda, and put your finger over the top of the straw. Lift the straw out, put it into the balloon, and blow or tap gently.)
 
3. Stretch the open end of the balloon over the neck of the bottle. Make sure it's on tight! Let the heavy end of the balloon dangle, so no baking soda goes in the bottle.

4. Hold onto the ballon at the bottle neck, and pick up the heavy part of the balloon so that all the baking soda falls into the vinegar at the bottom of the bottle.
 
5. Wow! Hear the fizz? There are thousands of bubbles! And look at what's happening to the ballon...