Faye Finney, age 12, of 5t. Augustine, Fla., for her question:

WHAT IS JET LAG?

Jet lag or jet exhaustion is something that happens when you fly by jet airplane to a far and distant time zone. Your body's timing is thrown dramatically off schedule.

You become most aware of the biological timing system of the body on a long trip. A flight from Los Angeles to London that leaves California in the late afternoon will arrive in England as Londoners are just starting a new day.

Your rhythmic system will still be working on California time. By London time, you will have insomnia at night and be sleepy during the day. This rhythm is called your biological clock and it is out of adjustment.

Your biological clock will reset itself, but it may take several days. As a result, your body functions will be out of rhythm, your efficiency drops and you feel tired.

Some investigators believe that better knowledge of biological clocks and the rhythms they control will help scientists find ways to use the rhythms for man's benefit. The ability to control body rhythms may also influence man's success in exploring space and surviving in it.