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.


  1. Because of all the 3D modeling programs I have, I'm starting to get the hang of this metric fad.

    1. If you think of a meter as about a yard (3 feet), the conversion-in-the-head thing seems to work for me ;)

  2. I loved the World Builders Handbook in MT days - I had a notebook filled with scribbles, ideas and UPPs and it was rarely out of by backpack so I could do stuff on the train going to/from Uni! Before these new fang dangled PC programs that do the same thing and real GMs rolled dice that is...!

  3. And in addition to Jules Verne, champagne and pastries, you now have something else to thanks the French for! :-)