(SSGX Origins) Let's make a Wipeout game! This time for real!

[Xpand]

Ok, the momentum of an object is what defines the quantity of motion that object has. It's a vector, so it has magnitude and direction. It's expressed as p=m.v in which "m" is the mass of the object and "v" is the velocity of the object (also a vector). The relation of that with jumping is that the more momentum an object has the longer it jumps if it's launched from a ramp. So you can see that it's not only the magnitude of the velocity (speed) that counts. The mass of the ship also counts for the length of the jump, but not for the height.
http://en.wikipedia.org/wiki/Momentum
You can relate the momentum to force through Newton's second law of motion with F=dp/dt, where the resultant force vector is the derivative of the momentum to time.

I just don't understand how you want to get gravity from this since the airborne time doesn't depend on the mass nor the horizontal speed.
I thought that Unity had an internal bullet physics engine with active gravity.

If what you need is the gravitic acceleration, then that's g=9.807 m/s^2

In another note you can also use the momentum to determinate collision dynamics:

dpsys=0 The variation of the system's momentum is zero ALWAYS (only if you DON'T have a variation in mass, which we do because ships burn fuel, but that makes things much more complicated).

Then if you have two ships colliding, the system's momentum will be

pinitial=pfinal (remember, always a vector)
Ship1 and ship2

p1i+p2i=p1f+p2f

m1.v1i+m2.v2i=m1.v1f+m2.v2f (velocity is a vector)
(v is velocity and m is mass)
This is for elastic collisions, which are the ones we want.
The problem is that I didn't consider drag here, so the ships would just bounce around the track's walls after they hit...