Why does ice float? Answer kids' tricky science questions with three simple experiments.

Don't let wintry weather put a freeze on your creative lesson plans. Even if you're trapped indoors without much money or supplies, it's easy to conduct fun, eye-opening science experiments that celebrate what's unique about the winter weather.

* Kid Question: "Why does ice float?"

THE ANSWER: Water has different states, including a liquid and a solid form. And since the solid form--ice--is less dense than liquid water, ice can float.

WHAT YOU NEED: Plastic cups, water, and ice cubes.

HOW TO DO IT: First explain to your students that all things (matter) take up space and have weight. When water freezes into ice, it takes up more space. Demonstrate this by pouring an equal amount of water into two cups, and freezing one overnight. The cup holding frozen water will be more "full" than the water cup. But both cups still weigh the same amount. That means the water's weight gets spread out over a larger space when it freezes into ice. Ask students what they think will happen if you placed an ice cube into the water. Will the cube sink or float? Check their predictions by having them carefully drop a cube into water.

Have students test out other objects' density relative to water. Ask students to choose a small classroom object, such as a piece of chalk, a paper clip, or a piece of Styrofoam. Have them describe their object and whether or not they think it will float in the water. One at a time, each student can place an object into the other water-filled cup.

TAKE IT FURTHER: Help students understand more about density by making a layered column of different liquids such as syrup, vegetable oil, water, and rubbing alcohol. Gently pour each liquid into a tall jar, and let them settle. The less dense liquids, of course, will rise to the top.

* Kid Question: "Why don't the penguins in Antartica get cold?"

THE ANSWER: To keep warm, a penguin has special adaptations, including a torpedo-shaped body. (Its body has less surface area relative to its volume.) With less area exposed to the chilly elements, a penguin doesn't lose as much heat as an animal with larger surface area.

WHAT YOU NEED: Thermometer, pie pan, 1-liter soda bottle with the top half cut off, and water.

HOW TO DO IT: Give your students an everyday example, such as the way a steamy slice of pizza can turn cool and rubbery if left out for too long. Then, ask students if they would expect a thin slice of pizza to cool off slower or faster than that same slice smashed into a ball. (The thin slice would cool first because it has a greater surface area relative to its weight.)

Pour two cups of warm water into each of the following: a pie pan and a 1-liter bottle. Use a thermometer to measure the temperature of the water in each container. The temperatures should be equal. Make a chart on the board and record the measurements as well as students hypotheses on which container will cool fastest. Set aside the containers for 20 minutes. Measure the temperatures again and record each on the chart. Which container had the coolest water? How do the results relate to a penguin's body?

TAKE IT FURTHER: Discuss other ways animals stay warm. For an activity on animal insulation, check out "Life in the Arctic Tundra," Instructor, January/February 2004.

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* Kid Question: "How come you can see your breath outside on a cold day?"

THE ANSWER: Your steamy breath is the result of a process called condensation, in which water vapor turns into liquid.

WHAT YOU NEED: Glass jar with lid, water, ice cubes, and food coloring.

HOW TO DO IT: If it's cold outside, have students go to the windows and exhale onto the glass. Explain that the "cloudy spot" is a bunch of tiny water droplets. Cold air can't hold as much moisture as warm air. So when you blow your warm breath onto the window, the vapor turns into tiny droplets.

Have your students work in groups and prepare a jar filled halfway with cold water. Then, add ice cubes until the water nears the top. Add drops of food coloring. Seal on the jar's lid and wait 10-15 minutes. Have students observe the outside of the jar. Is it wet? Are the droplets clear, or the same color as the water inside of the jar? (The droplets should be clear, which shows that the water formed from vapor outside of the jar.) Just as tiny droplets form on the chilled jar, when you breathe warm air into the chilly outdoors, tiny water droplets form a steamy cloud.

TAKE IT FURTHER: What would happen if you exhaled onto the outside of the ice-water-filled jar? Test it out. Then, walk outdoors with your students. Notice the dew-covered ground. When temperatures fall at night, water vapor near Earth's surface condenses into tiny water droplets that coat stems of grass.

RELATED ARTICLE: Answers to more "WHYS"

WHY do you shiver when it's cold?

To prevent hypothermia, your brain monitors temperature very closely. If the surface of your skin cools below the healthy temperature, receptors on the skin send signals to the brain. Result: Your body's muscles begin to contract and release in quick bursts. This "exercise" generates heat to help bring your body temperature back to normal.

WHY do animals hibernate?

During the winter, when food is scarce and temperatures can be brutal, many animals take a long nap, or hibernate. And since they can't eat during hibernation, animals like the black bear get vital energy from stored body fat. To prepare for the food-free stint, a black bear feasts during the fall, gaining about 30 pounds every week. That weight has to last for up to 100 days of hibernating.

WHY do trucks pour salt onto icy roads?

Pure water freezes into ice at 0*C, or 32*F. But when salt mixes with water, the freezing point is lowered to around -16*C, or 3*F. Road workers pour salt onto roads before and during a snowstorm so that water will stay in its liquid form (instead becoming slippery ice) at much colder temperatures.

WHY are winter days shorter?

Since our planet is tilted along its axis, the amount of sunlight reaching different regions changes throughout the year.