Chad notes, in response to PZ's rather absurd assertion that biology is the only Dumped Upon science, and that physics is so well treated in movies and TV, that "Most of the SF movies I see are lucky if they can get Newton's Laws right, let alone any of the finer points of astrophysics."
Indeed, this was the topic of one of the two talks I gave at Hypericon a couple of weeks ago.
Let me try to explain one aspect of this: specifically, the motion of space fighters.
Don't get me wrong. Star Wars is a great movie, one of my all-time favorites. It's even still a pretty good movie if Han doesn't shoot first, even though that's an absurd change on so many levels. But Star Wars wrecked the popular perception of how space fighters would move in space for a long time. The basic problem is, they move like airplanes.
There are two things about an airplane's motion that the Star Wars fighters do, even though they shouldn't have to. First, an airplane is always moving in the direction it is pointing. if you know Newton's laws, you will ask, "moving relative to what?" Well, relative to the air that it's moving through, of course! If they didn't, they'd fall out of the sky, for they are aerodynamically designed to fly by pushing up off of the air. But there's no air in space; the density of gas even in high earth orbit is lower than the density of gas in the hardest vacuum we can create in the lab on Earth. If your space fighter only has reaction engines that point in one direction (as is the case, at least, with the X-wing fighters of Star Wars), then they have to point in the direction that they are accelerating... but not in the direction they are moving. All those Y-wing pilots who died attacking the Death Star because they had TIE fighters on their tails whom they couldn't shake? A tragedy of misunderstood physics. They didn't have to loop around to fire at the TIE fighters, the way airplanes do; they could have just turned around in place!
The second thing Star Wars routinely gets wrong is that fighters in space do not have to bank. When an airplane turns, it banks. Think about being in a car going quickly around a curve. You're more likely to maintain control of your car if the road is banked. Look at a high-speed racetrack sometime, and you'll notice that the curves are banked. What's going on is that to turn to the left, a vehicle needs some acceleration pointing to the left of its current direction of motion. With a car on a flat road, that acceleration is provided entirely by friction between the road and the tires. On a banked road, some of that acceleration is now provided by the road pushing up on the car. Similarly, with an airplane, the main force of the air on the plane is the air pushing up on the wings, generating lift. If an airplane wants to turn left, it banks so that the bottom of its wings are pointing to the right. This, combined (crucially!) with the plane's motion, gives it some acceleration to the left, allowing it to turn.
In space, there is no air to bank off of! Once again, things work differently. First of all, these space fighters are all (approximately) in freefall. They're either in deep space, or they're in orbit about a planet, so there is (effectively) no gravity to fight. Second, without air, they can't bank off of it. Want to go in a different direction? Point your engines in the direction such that the acceleration applied to your current velocity vector (relative to whatever you're measuring your velocity relative to) will give you a velocity in the direction you want.
What would this look like? It would look weird to those of us who are used to things flying like airplanes or, alas, flying like the fighters in the worlds most popular space movie epics (where the space fighters fly like airplanes). But sometimes it's done right. The new Battlestar Galactica series tends to do it pretty well. Before that, though, back in the early-mid 1990's, the TV show Babylon 5 (still my favorite) explicitly had space fighters obeying Newton's laws. It was a rare gem to see, and it warmed my physics nerd heart. (I'm the kind of guy who gets a warm and fuzzy feeling to hear the pilot of a science fiction fighter say "coordinating vectors for grapple." Look! Technobabble that actually means something and makes sense!)
The very first episode of the series (after the pilot) was "Midnight on the Firing Line," and it showed a space combat between a group of raiders and a squadron of Starfuries (which are well designed space fighters; whereas X-wings look cool, Starfuries are cool and look like they were designed for Newtons-laws-obeying space!). At one point, Commander Sinclair has a raider (in a little potato chip ship) on his tail:
If he was in a Y-wing, I guess he'd just have to die. (Indeed, he does take some fire— you can see it happening there— but he was hoping for a surrender.) Instead, though, what does he do?
In the picture above, you see him just starting to turn around. The asymmetric firing of the engines makes sense given the direction he wants to turn. Does he have to bank or loop around or anything like that? No. He just points in the other direction. His fighter continues to move in the same direction relative to the larger ship as it had been, but now he's got his guns pointing in the right direction:
much to the dismay of the raider:
Here, also, you can see that Sinclair is accelerating away from the exploding raider ship. Probably not a bad idea; there will be debris coming away from it. Also, a line he said before turning around suggested that he was slowing himself down relative to the raider, so it was probably approaching him at this point; he'll want to get away to avoid a collision.
There are other great tidbits of space fighters qualitatively getting Newton's Laws right in that scene, and in other scenes from Babylon 5. Indeed, the fact that the Raiders have ships that look like flying wings is explained; Sinclair says that they are designed for both space and atmosphere, and as such the wings are good vulnerable points to shoot for.
More often, though, when you see something with ships flying about in space, not only do they make sound (which happens even in B5), but they fly like airplanes. Very few people realize the degree to which this is a violation of Newton's Laws. Kudos to Babylon 5 for trying to get it right.