a = (Ft - Fr) / m
Ft = force of thrust
Fr = force of resistance

That's OK. I have a 100 fribble ship which has 10,000 olphlaphs of thrust, but it's still the same physics.

Same question as "how big is that spaceship?". It doesn't matter if it's 100 millimeters or 100 billion miles, it's still the same sprite . . .

If you want real world units to give to your users, I'd recommend SI (meters, seconds, kilograms) but it doesn't really matter. For the sake of floating point accuracy, I like to make everything work internally with values in the region of 1, so if all my objects have a real world mass of 175 kg, then 1 of whatever-it-is-Im-using is about 175kg. *shrug*.

Quote:Original post by Cannibal_Coder
a = (Ft - Fr) / m
Ft = force of thrust
Fr = force of resistance
a = 100...100 what? neutons? fly farts? Leaf Blowers?

Well, if Ft is in units of fly farts, and m is in units of Leaf Blowers, then "a " is in units of fly farts per Leaf Blower.

I strongly advise you to use sensible units!! For example, basic units of kg for mass, m for distance, seconds for time, and derived units like Newtons for force. So, in the case of

F = m * a

m is in kg

a is "meters per second per second" = m/(s*s)

F is in Newtons

so a Newton (derived unit) has units kg * m / (s * s)

It's really useful to understand units - if you have an equation you can quickly check to see if it is incorrect by checking the units are consistent. For example, if someone wrote something like:

F * t = m * a * distance

The left hand side has units Newton * seconds = kg * m * s / (s * s) = kg * m / s

The right hand side has units kg * (m / (s * s)) * m = kg * m * m / (s * s)

Since the left/right hand sides have different units, you can tell very quickly the original equation is simply wrong. If it's a more complicated expression you derived yourself, it can even give you clues as to where you went wrong in your derivation.

Of course... just because the units for an equation work out doesn't mean to say it's right!

Google "dimensional analysis".

Quote:Original post by Cannibal_Coder
in what units of measurement though? Say I have a 100 ton ship (in space) with engines that put out 10,000 lbs of thrust....uhh...yeah.

Use metric units (as in the post above).
100 (metric) ton ship, with 10,000 N thrust:
10,000 N / 100,000 kg = 10,000 kgm/s^2 / 100,000 kg = 0.1 m/s^2

Also consider taking basic physics courses at your school or find basic highschool text books on physics from your local library.

EDIT: Fixed a typo.

[Edited by - FlowingOoze on July 1, 2005 12:15:39 PM]