# Weight vs Mass On Moon and Mars Imperial Units

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1. Sep 3, 2013

### BigJon

1. The problem statement, all variables and given/known data
Moon's gravity is 5.31ft/sec^2 An object has the weight of 3.5 lb-f on the moon. What is its lb-m
What is the lb-m and lb-f on Mars with gravity of 12.1 ft/sec^2.

2. Relevant equations
w=mg=mg/gc

gc= gravitational constant----> 32lbm*ft/sec^2 for earth

3. The attempt at a solution
So I understand mass is the same everywhere. Also lb-m and lb-f are the same numerically on earth but not on other planets?

Im just really confused with imperial units because i dont understand when to use or not use the gc.

2. Sep 3, 2013

### voko

$1 \ \text{lbf} = 32.174 \ \frac {\text{ft} \cdot \text{lbm}} {\text{s}^2}$.