• The term g-force is a measurement of a person's apparent weight in a ratio of its normal weight.
\begin{align} g-force = \frac{Apparent Weight}{Normal Weight} \end{align}
  • Within a rocket, an astronaut experiences both gravity and the acceleration from the Thrust of the rocket.
  • Thus, he would feel the reaction between him and the ground (mg) and the acceleration of the rocket. (ma)
  • His/her apparent weight can therefore be given by: $mg + ma$. (Newton's 2nd Law)
  • Therefore, their g-force can be determined by:
\begin{align} g-force = \frac{Apparent Weight}{Normal Weight} \end{align}
\begin{align} g-force = \frac{mg + ma}{mg} \end{align}
\begin{align} g-force = 1 + \frac{a}{g} \end{align}
  • NB: This is ONLY when the rocket is VERTICAL. If it is horizontal, it is simply:
\begin{align} g-force = \frac{a}{g} \end{align}
  • This method of describing force has some advantages:
    • It is easier to compare forces with different people as it depends only on the person's weight.
    • It is numerically easier to interpret than the normal force system.