David Dame, age 10, of Tekamah, Neb.,, for his question:
What causes absolute zero?
When the thermometer rises to 100 degrees, we have a very hot day. But on the face of the sun, the temperature rarely falls below 11,000 degrees. The seething heart of the sun reaches million of degrees and some stars are much hotter than our sun. There is no limit to how hot things can get. But scientists think that there is a limit to how cold they can get. This limit of coldness is called absolute zero.
Cold is merely absence of heat. So to find out what causes absolute zero we must first find out what causes heat. It is, of course, a form of energy. A hot drink merely has more of this heat energy than an ice cube. However, an ice cube has some heat energy, maybe a good deal. 'T It is quite a bit warmer than dry ice.
Every substance, from solid lead to filmy gas, is made of tiny atoms and molecules. In a hot substance, these particles are full of heat energy which they use to rush around at great speeds. In a cool substance, the particles have less heat energy with which to rush around. It is believed that they move around more slowly.
Heat energy, then, is motion is the tiny particles from which a substance is made. In solids and liquids, these particles are held together by attraction fcr one another. Heat energy tends to break this attraction. When water gets hot enough, the energetic little particles break their attraction for one another and fly off into the air as separate particles of gas„
At ordinary temperature; water is a liquid. Its particles have enough energy to more freely, but not enough to break the attraction which makes them cling together. At freeing point, they lose so much energy that they can no longer move freely. They lock together in latticework to form solid ice. However, they may still have enough heat energy to jostle each other and vibrate.
Heat is one of the easiest forms of energy to notice. A warm substance gives up its heat energy to anything which touches it. We measure heat in degrees a day of 100 degrees is 10 degrees hotter than a day of 90 degrees. This measurement is on the Fahrenheit degrees, which we use for the weather. On it, water freezes at 32 degrees and boils at 212 degrees. On the Centigrade scale, water freezes at zero degrees and boils at 100 degrees. Frozen water still has a great deal of heat energy.
Scientists believe that water, and everything else, can get as cold as minus 273 degrees centigrade which is the same as minus 459 degrees Fahrenheit. At this point, we are told, a substance has absolutely no more heat energy left. It has reached absolute zero. (Scientists use two special temperature scales for measuring things near this chilly temperature. The kelvin scale measures in degrees equal to centigrade degrees. The Ranking scale measures in degrees equal to Fahrenheit degrees. On both scales, zero equals absolute zero.