In case the name didn't give it away, I like science fiction. A while ago (more than a year ago) I decided to look into space combat from a scientific standpoint. After spending huge amounts of time procrastinating from real work by looking up laser efficiencies, theoretical maximums for focusing particle beams, physical constants for a number of potential armor materials, and so on, I find that there are things about the physics that Google simply won't tell me. So I'm hoping some of you might be able to help me with these questions. (I'll probably have more, too - this is just the list I came up with now.) Some of these answers might be complicated - I think I can handle it, if you are all nice and use small words. I am a PhD student, but in zoology. I've had a brush or two with physics, science is no stranger, but my territory is the ecology of grasshoppers, not something even remotely related to the subjects I'm asking questions about. Anyway, thanks in advance for the help. 1) How does one compute acceleration per meter of barrel length for a railgun or coil (gauss) gun (also called a mass driver)? Clearly, each additional meter of length gains you less acceleration, since it has less time to act on the projectile. Equally clearly, higher velocities give you a greater chance of hitting a maneuvering target. And, of course, at a certain point the barrel length just gets ridiculous, even for a zero-drag environment. Before someone points out the obvious, I know that railguns and gauss guns are really different beasts - I'm looking for an equation for each. 2) What is a plasma mirror? Something I read suggested that a plasma mirror reflects any light below the mirror’s frequency. What does this mean? Is it true? If so, can a plasma mirror withstand intense blasts (weapons-grade pulsed lasers, for instance)? (And is a plasma mirror related to a "plasma window"?) 3) How do you calculate the speed at which a gas or plasma expands? For instance, if you lose containment on your spacecraft’s fusion reactor, how do you calculate how rapidly the no longer contained plasma takes to expand? 4) I assume there must be a way to take known physical properties of a material (density, possibly distance between nuclei and bond strength as well) and calculate how well it stops particle and EM radiation (of, obviously, known characteristics, since x-rays and hypervelocity charged particles have separate characteristics). How does one do that? 5) To keep things all about the plasma, a question about beam spread. If you are busy letting plasma blast out of an electromagnetic bottle, either to provide propulsion, or to burn your enemies to cinders, how does one calculate beam spread? For a particle beam, I’d look at particle velocity from heat, time to target, and calculate how far off the beam axis a particle could wander from thermal issues in that time. But for a plasma beam, the thermal velocity is the (potentially insanely high) velocity of the “bolt” itself. A well-designed mag bottle should be coming as close to possible to forcing every last ionized particle to fly out along the beam axis, with no wandering. 6) Is there any way to take a known set of shapes with known mass colliding at a known velocity and determine from that information the impulse of the collision? 7) There’s a design out for a magnetic sail spacecraft that is supposed to be shoved around by a beam of plasma shot from elsewhere. I’m aware of the basic interactions of charged particles and magnetic fields, but in this case something is puzzling me. Does the sail stop the beam? Initially, I assumed the beam would “splash” against the sail, electrons going one way, ions going (slightly less readily) another. Then I did some calculations (which, I am sure, were awful for numerous reasons) that suggested that no reasonable field could exert the forces to cause that much charge separation, and that the charge separation would keep the beam together, and let it barrel on through the sail. So what really happens?