Karen Roberts, age 11, of San Diego, California, for her question:

What causes house dust?

Every present and future housewife has pondered this wretched problem. Every household proves beyond doubt that dust is eternal. You mop the floor, wipe the furniture and pause to admire the spanking clean surfaces. But not for long. Another layer of dust arrives from who knows where and the job waits to be done all over again. There is no end to it and naturally you wonder where all the dust comes from. Actually it is small fragments of matter, light enough to float suspended in the air. At least for a while. In a calm room, these dusty particles have a chance to sift down through the air and settle in misty layers on your freshly polished surfaces.

The next quandary is how all those fine fragments get into the sir. The answer to this takes us to the nature of solid materials. Even the most durable materials are always wearing away. Small fragments break off from floors and rugs, walls and ceilings. Most of them are too tiny to notice but after many centuries a whole house flakes away and crumbles into particles of dust. This constant wearing away creates most of our pesky house dust. More is caused by particles of smoke and  fumes, some blows in through doors and windows and some is tracked inside on dusty shoes