G-Forces

- 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}

(3)
\begin{align} g-force = \frac{mg + ma}{mg} \end{align}

(4)
\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.

- It is easier to

page revision: 5, last edited: 30 May 2011 10:52