## Saturday, 7 April 2012

### A to Z: G is for Gravity

Most ships in Traveller have a Manoeuvre Drive. A large percentage of ships have a Jump Drive as well and are defined as Star ships. Manoeuvre Drives are rated in units of acceleration, “g”, from 1G to 6G, where g=dv/dt.

Planetary bodies have surface gravity. On Earth, gravity at the surface is 1G or 9.806 m/s^2. The value of G on other planets is found by the Traveller Book 2 formula G = K(R/4) where G = Surface Gravity, K = Density of the planet in relation to Earth and R = Radius of the planet (which is half of the Diameter statistic discovered during planetary generation).

The ‘real physics’ formula is g =G* M/r^2 where g = gravity, G = the Gravitational constant of 6.67*10^-11, M = Mass, and r = radius of the planet. Unfortunately, you have to convert the mass into kilograms and the radius into metres, and then my brain explodes.

I think the Traveller Book 2 formula gives a result that is pretty workable for a game.

Play roleplaying games and learn physics at the same time.