Albert Rich, age 9, of Huntsville, Ala., for his question:

WHY DOES FIRE MAKE SMOKE?

Fire is a chemical change. All the solid, liquid and gaseous materials are made from atoms and mini molecules. When a chemical happens, the molecules are broken up into different materials. Some of the atoms are remodeled to make different molecules. A blazing fire uses oxygen gas from the air to keep going. As it burns, it breaks up molecules such as wood or coal and gives off heat.

Wood comes    from trees, and coal comes from trees that died long ago. 'Plants use hydrogen and carbon to build all sorts of hydrocarbon molecules. In the fire, these molecules break apart‑‑and tiny fragments of carbon pour out as plumes of smoke. Hot air from the fire rises, which is why the flames and smoke tend to move upward. Meantime, all sorts of other changes are happening in the fire.