Cindy Thompson, age 15, of Atlanta, Ga., for her question:

WHAT MAKES ICE FLOAT?

You notice, of course, that ice cubes float at the top of your glass of fruit punch or water. The reason for this is that ice is lighter than water  and therefore it floats in water.

Water will turn into ice at 32 degrees Fahrenheit or zero degrees Celsius. When water freezes, it increases its volume by one eleventh. This means that when 11 cubic centimeters of water freeze, 12 cubic centimeters of ice will form. Thus it is easy to see that ice is lighter than water    and that it will float in water.

This expansion of water by freezing also explains why you sometimes hear about frozen water pipes splitting in winter, and why freezing water in an automobile radiator can damage a car.

After water freezes, it continues to get colder until it has the same temperature as the surrounding atmosphere.