Scienceville
Experiment Time!
Can hot water freeze faster than cold? Why does ice float? How can an insect walk on a pond? Let's explore the surprising science of water!
Did you know?
In 1963, Erasto Mpemba, a schoolboy in Tanzania, noticed in a cookery class that a hot ice-cream mix froze before a cold one. It is now called the Mpemba effect, but scientists still argue about whether and why it happens!
Water takes up about 9% more space when it freezes. That's why ice floats, and why a full bottle of water can crack in the freezer. Because ice floats, ponds freeze from the top, and fish stay safe below.
Water striders (pond skaters) are insects that walk on water! Their long legs spread out their weight, and thousands of tiny water-repelling hairs keep them dry. They can zip across at a metre per second or faster.
Try this: Float a Paper Clip
Do this with an adult
With an adult, fill a bowl with water. Place a small square of tissue paper on the surface and gently lay a dry steel paper clip on top. Wait for the tissue to soak and sink. The clip keeps floating! Water's thin 'skin', called surface tension, holds it up. Now add one drop of dishwashing liquid near the edge. What happens?
Go further: Rain That Freezes When It Lands
Sometimes raindrops fall through freezing air but stay liquid, even though they are colder than 0 °C. Water that stays liquid below its freezing point is called supercooled. When these drops touch a cold road, car or tree branch, they freeze quickly into a clear coat of ice called glaze. This is freezing rain. Thick glaze can make branches snap and weigh down power lines. It is the same quick-freeze trick you saw in Snap Freeze!