1 g is equal to the gravitational acceleration on earth which is equal to 9.8 \(m/{s^2}\). G force is the vector sum of non-gravitational and non-electromagnetic forces. G force is resistance as a result of mechanical forces to the object. When an object is in free-fall under the influence of gravitation, the condition is known as zero-g. G force is experienced by the aircraft pilots. 

Pilot sustain g forces along the axis of the spine. There is a variation in the blood pressure along the length of the body. There is a limit to the maximum g forces which can be tolerated by a human body. A positive vertical g force can cause a blackout, G-LOC, or even death if g force is not quickly reduced.