Elsie Beard, age 13, of Missoula, Mont., for her question:

WHAT MAKES ICE FLOAT?

You notice, of course, that ice cubes float at the top of your glass of water or fruit punch. The reason for this is that ice is lighter than water. Because it is lighter, 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 easy to see that ice is lighter than water and that it will float on 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 perhaps cause damage.

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