Marton Manson Jr., age 14, of Cumberland, Md., for his question:
CAN YOU EXPLAIN A VACUUM?
A vacuum is a term taken from the Latin word •'vacuus," which means "empty." A vacuum is a space which has no matter in it.
Scientists tell us there is no such thing as a vacuum, because all space as we know it contains some matter. In practice, we speak of a vacuum as a space from which most of the air or other gas has been taken, and in which the pressure is extremely low. But this is only a partial vacuum.
No one has ever created an absolute vacuum. An absolute vacuum would be an enclosed space from which all the air has been taken out. We cannot do this, even with the most powerful air pump or by chemical means.
In the air we breathe, there are about 400 billion billion molecules of gas per cubic inch. Man can create partial vacuums in which there are only a few million molecules per cubic inch.
Among the most nearly complete vacuums that have been attained is one in which the pressure of the gas is about one ten thousand millionth of the normal pressure of the air.
Scientists speak of high or low partial vacuums, depending upon how completely the air or any other gas has been taken out of an enclosed space. Any space in which the pressure is about one thousandth of that of the atmosphere is usually called a vacuum.
The important thing about a vacuum is that it is usually a useful emptiness. For example, if we create a partial vacuum in any space, water or any other fluid may enter into it. we make use of this principle in drinking lemonade through a straw. We do not pull the liquid up through the straw. Instead, by sucking on one end of it, we take out some of the air that is in the straw. The air outside exerts pressure on the liquid and forces it up and out through the partial vacuum in the straw.
The gasoline intake of an automobile motor makes use of this same principle.
The vacuum cleaner is a good example of the usefulness of a vacuum. Air flows into a partial vacuum and carries dust and dirt into the collection bag of the machine.
In a vacuum bottle, a vacuum prevents heat from entering or leaving by conduction or convection.
Most electronic tubes contain a high vacuum. This keeps the air or gas inside from being affected by the passage of electrons across the tube.
Television picture tubes, cathode ray tubes for oscilloscopes and other kinds of electronic tubes cannot work unless most of the air is pumped from them. The partial vacuum inside the tube keeps the hot filament from burning up and allows electrons to flow.
In some vacuum tubes in use today, as much air as possible is taken out of the tubes by means of an air pump. Then a chemical called a "getter" is placed inside the tube. This increases the vacuum by combining with a large part of the remaining air inside the tube. The chemical coats the inside surface of the vacuum tube.