Shane Rush, age 17, of Fargo, N.D., for his question:

HOW IS ENTROPY USED?

Entropy is a property of matter. Scientists use it in connection with thermodynamics, the study of heat and work. The entropy of a substance increases whenever the energy it possesses to do work decreases.

As an example, steam entering a turbine has a low degree of entropy because it can do work by moving the turbine shaft. After moving the shaft, the energy of the steam has decreased and thus its entropy has increased. The total entropy of the universe is increasing because, in time, all matter tends to lose available energy.

Entropy is also used as a measure of the internal disorder in a substance. The atoms of a diamond are orderly because chemical bonds lock them in a rigid framework. But the atoms of helium gas in a balloon are disorderly because they shoot about inside the balloon. A diamond has lower entropy than helium.

The science of information theory uses the concept of entropy to describe how faithfully a system can handle information. A system that has a high degree of unpredictability has high entropy.