Kerry Carnohan, Age 10, Of La Jolla., Calif., for his question:
Why are frozen things so hard?
Most of our everyday world is frozen solid, even in the sweltering heat of summer. Your bike, your tv set, the house in which you live are solid objects, because they are cool enough to freeze to a solid state. But if you put most of these things into a blast furnace, they would melt to runny liquids and finally become gases and boil away.
The day's weather may dip down below zero or rise above 90 degrees. The seas and the dry land, the air and everything around us feels the sun's heat which falls upon the face of our world. And all these things which make up our world are made from particles of matter too small for our eyes to see. We call them atoms and molecules.
Atoms and molecules are restless particles, always eager to move around. They get their energy from heat the more heat they get, the faster they move. Oxygen gets enough heat from everyday temperature to fly off as separate molecules of gas. When you put an iron poker into a furnace at 1539 degrees centigrade, its atoms get enough heat energy to flow freely as a liquid, and the solid metal becomes molten iron.
Gases and liquids become solid when they lose the energy they get from heat. As the temperature drops., the free. floating molecules of oxygen gas slow down and down. If the temperature falls far below zero, the oxygen gas becomes liquid. Its molecules are now so close that they touch and cling to each other. But they still have space and freedom to move around.
If the temperature drops still lower, say to minus 208 degrees, the molecules of oxygen have only enough energy to shiver and vibrate. Because the tiny particles have an attraction for each other, they pack together in a close mass. They form a hard and icy lump of frozen oxygen.
Every substance has a certain temperature at which it freezes solid. This is its freezing point. The freezing mint of water is zero degrees centigrade. At this temperature, its molecules have not enough energy to flow. They jam pack together in a fine lattice work, and the liquid water becomes a hard lump of chilly ice. Ice anc) other frozen substances are hard because the atoms and molecules are packed closely together in a dense, solid mass.
The everyday temperature is warm enough for the gases of the air to reach the boiling point. Iron and wood, glass and lead, stones and all the other solids around us reach their freezing point at everyday temperatures. Water reaches its boiling point and turns to gassy steam at 100 degrees centigrade. On a frosty morning, its molecules cannot get enough heat to keep moving. As they slow down, they pack in a tight wad of hard and solid ice.