# Relative Gravity

The 'Relative Gravity' calculation is based on a very, very rough calculation using the relative densities and radii of planets from the Sol system. The figures are taken from the IBM World Book 2000 and then applied to their equivalent world types in FFE. The densities are expressed in either grams/cubic cm, or kilograms/litre, or tons/cubic metre, all three use the same ratio.

I performed the calculations on Mars, Venus and the Moon using their respective masses and radii, and then compared the results to their known relative gravities using data from the IBM World Book. The calculations provided fairly accurate results:

- The figures from the IBM World Book:
- Mars: 38%;
- Venus: 88%; **the Moon 1/6 (or 16.6% recurring).

- My own calculations:
- Mars: 35.11%; **Venus 88.55%; **the Moon 16.11%

The densities for the different planet types in Frontier are as follows with the comparative planetary body in parenthesis:

- Small Barren Rock and Barren Rocky Planetoid (the Moon): 3.27
- Rocky Planet with thin Atmosphere (Mars): 3.65
- World with Methane Weather System (Venus): 5.17
- Planet with Oxygen Atmosphere (Earth): 5.45
- Small Gas Giant (Uranus): 1.24
- Medium Gas Giant (Saturn): 0.62
- Large Gas Giant (Jupiter): 1.25

To calculate the relative gravity, *i.e.* relative to Earth's, of your chosen planet do the following:

- 1) Calculate the total mass of the planet by multiplying its relative density (expressed in Earth masses) by the mass of Earth, 6,000,000,000,000,000,000,000 metric tons.

- 2) Calculate the volume of the planet by multiplying the total mass of the planet by the applicable density.

- 3) Next, use the formula for calculating the volume of a sphere in order to determine the radius of your planet:

Volume = (4 / 3) * (pi * (r ^ 3))

- 4) Then multiply the radius of your planet by its relative density to calculate its Estimated Gravitational Pull (EGP).

- 5) Finally, to compare the EGP of your planet to that of Earth, divide the EGP by Earth's, which is 35.237. This will give you a Relative Gravity figure which is expressed as a percentage.

## Links

- Newtonian modelling
- FIA Galactic Factbook Ackedze Source of this page
- Distance (Oolite)