Originally posted by Low Orbit
What I don't understand is if there is no friction in space what does it matter how large something is(what the mass of an object is?)
with out forces from outsidea system always keeps it velocity. This is a nature law and is called conservation of Momentum.
Conservation of Momentum:
You are right there is no friction in space and so there is no loose of momentum (speed) for a system and it doesnt matters the mass it has.
The mass of an onbject comes in play when you want to change it's velocity (or momentum) and is technical simple a proportinal constant that tells
you how much force you have to aplay to increse or decrease its velocity to a specific amount in time.
This is the second law of newton. You will probabily know it as
F = m * a (for m = const)
where F: the force you need,
m: the inertia mass ('resistance' factor of velocity changeing).
a: acceleration or the change of velocity per time (dv/dt)
Basic Physic (Newton's Law):
Why 'objects' have mass at all is unknown and still a hot topic of sience.
The nature behaves like that. But why and why not completly different? No one knows...
To your question about cern in space. Basicly that's a rocked engine like the classic one or the ion engine.
They all have in common that the throw away mass form itself in order to accelerate the mass left (your spacecraft).
this is done because the Conservation of Momentum:
p total = m1 * v + m2 *v
whereas the v is velocity and has a direction.
lets say m1 is the spacecraft mass and m2 the stone (the particle) you want to throw away.
the momentum of your system (spacecraft AND stone) stays constant.
So before you throw you can write:
p total bevore = (m1+m2) * v0
where v0 is the initial speed of your system (spacecraft and rocked)
and after :
p total after = m1*v1 + m2*v2
but p total before must be equal P total after!
(m1+m2)*v0 = m1*v1 + m2*v2
be aware that v1 and v2 are vectors! Now your velocity v1 of your spacecraft after the ejection of the stone dependents on how FAST (v2) you ejected
v0 = 0
v2 = -1000 m/s
-> 0 = 1000kg * v1 + 1kg * -1000m/s
your spacecraft end speed is v1 = 1m/s!
throw the stone faster!
v2 = -2000 m/s
-> 0 = 1000kg * v1 + 1kg * -2000m/s
your spacecraft end speed is v1 = 2m/s!
so what does this tell us?
Because your spacecraft has a limited fuel storage capacity (m2 mass) it will gain more speeed as faster you eject the fuel mass. This is known as the
(Note that for creating this formula the exact second law of Newton has to be used because the mass changes! that means not
F=m*a but F = dp/dt = d(m*v)/dt )
So a mini cern rocked engine would be a nice thing but only when you also have the energy from somewhere for that engine! the ion device you can see
as such a mini cern rocked.
last point..what is about the solar propultion?
That is a different! engine. Here you do not carry feul with the spacecraft. And therefore the end velocity you can archive is not limited to the
quantity of feul.
hte feul if you want so is the radiation of the sun. A pretty nice thing. You only need big 'sail' and a spacecraft with less mass (faster
acceleration) and gain a lot of speed over time.
so i hope i could help you a little with your question.
[edit on 10-5-2006 by g210]
[edit on 10-5-2006 by g210]