Tommy Nash, age 14, of Vancouver, Wash., for his question:

WHAT IS A "G" FORCE?

"G" is a symbol used to rate the forces that act on riders of any kind of vehicle    airplane, spacecraft or even the family auto.

The earth's gravitational force acts on a person whether he is stationary or moving at a constant speed. Gravity produces a standard acceleration (change of speed or direction) of "1 G." When a vehicle accelerates, additional forces are observed.

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

At 2 Gs, a person feels like he weighs twice as much as he does normally at 1 G. After several seconds at 5 Gs, a pilot's sight dims and he loses consciousness. He would be able to survive a force of 9 Gs for only a few seconds.