Grow your own snow
Bring winter into your kitchen. BONUS: It's a science experiment, so your parents won't even mind!
Ultracold + water vapor = crystals ... otherwise known as snow!
That's the basic formula for this science experiment—created by physics professor Kenneth G. Libbrecht—that creates a snow crystal growth chamber (or diffusion chamber) right in your kitchen. Read on to find out how to do this experiment, taken from the Nat Geo Kids book Try This Extreme.
Step 1
Cut the bottom 1½ inches off the soda bottle carefully. You will use both portions of the bottle.
Step 2
Using the bottom of the bottle as a template, cut the sponge so that it fits inside with just a little squishing. Use the pins to fasten the sponge, sticking the pins in from the outside, through the sides of the bottle and into the sponge.
Step 3
Thread the sewing needle with the string or fishing line and make a knot at one end. Push the needle from the outside of the bottle bottom through the center of the plastic, through the sponge, and pull through. The string or line should be about 12 inches long. (Hint: Our needle made a hole too big for our knot, and the string kept pulling through the sponge and falling out. So we tied one end of the fishing line to a button, then used the needle to push the end through the sponge again. The button kept the line from falling out.) Tie the paper clip to the end of this line. The paper clip will weigh down the string as it hangs.
Step 4
Place the smaller bucket inside the larger bucket, surrounding its bottom and sides with insulation material.
Step 5
Have an adult help you place dry ice in two plastic bags and carefully break it apart. Pour a layer of dry ice into the smaller bucket. Take the cap off the soda bottle and stand it neck-down in the bucket. Pour dry ice around it until the ice extends halfway up the sides of the bottle.
Step 6
Wet the sponge. Place it back in the bottle bottom if you’ve removed it. Fit the bottle bottom, with sponge inside, on top of the bottle that’s in the smaller bucket. Add extra dry ice as needed to keep the temperature cold as the crystals form. Small ice crystals should begin forming after 5 to 10 minutes.
WHAT’S GOING ON
Dry ice doesn’t melt, it sublimes. That is, it changes from a solid to a gas when it's warmed, producing carbon dioxide gas.
The bottle becomes a diffusion chamber, in which air is chilled at the bottom but warm at the top. This creates the perfect condition for crystals to grow.
The water evaporates from the sponge. The water vapor travels around the bottle, until the air inside it gets supersaturated, with humidity at more than 100 percent. Then vapor molecules attach to the string and form a crystal. The string provides a nucleation site where condensation can occur. In the atmosphere, dust crystals perform this purpose. There, supersaturated air condenses into water droplets if the temperature is above 32ºF (0ºC) and into ice crystals (snow) if the air temperature is below 32ºF.