Scott Wakefield, age 11, of Duluth, Minn., for his question:

WHAT IS A G FORCE?

The letter G is used as a symbol to rate the forces that act on riders in any kind of craft, whether an airplane, a spacecraft or a roller coaster at the fair.

The earth's gravitational force acts on a person whether he is stationary or moving at a constant speed. Gravity produces a standard change of speed or direction of one G. When a craft is accelerated, additional forces are observed.

When a pilot pulls his plane out of a dive, he feels extra weight like force. If his acceleration is twice the standard amount, it is rated at 2 Gs. This means the pilot's body must support twice as much force as normal.

After several seconds at 5 Gs, a pilot's sight dims and he loses consciousness. He could survive a force of 9 Gs only for a few seconds.