Tuesday, November 10, 2009

You too could be Joss Whedon

So far I've mostly harped on things in movies or video games that are bad, but it can be important to point out examples of good in science fiction as well.

There is one common issue in science fiction that is more drawn to light by the few shining examples where it was done correctly, rather than the majority of shows and movies that flagrantly ignore reality.
This issue is sound in space.

Any person can think of three or four shows where this is done incorrectly. This is usually because some high level person on the show forced them to include it because otherwise "it just doesn't seem realistic." The reason that this doesn't seem "realistic" to these executives is that they grew up in an atmosphere. In space, where there is no medium for sound to travel in, you can't hear anything. As the saying goes "In space, no one can hear you scream."

So, what are some movies and shows that did it right? First off, as was hinted at by the name of this post, Firefly. Whenever there was an outside shot of a ship that wasn't on a planet, the only sound you heard was music. This is a perfect example. It doesn't require annoying silence, and it worked quite well, dramatically.

Another example of someone doing it right, scientifically at least, was 2001: A Space Odyssey. In the extended director's cut, there was a scene where one of the crew was outside of the ship for about 10 minutes. During the whole scene, the only sounds are the hissing of air from his space suit life support system, and some communications. It made the scene feel very desolate and creepy, but it was paced a little slow.

There are ways, however, of using the silence of space for good dramatic effect. In the most recent Star Trek movie, the first battle featured some poor red-shirt getting fwooshed out of a hole in the hull of the ship. As the sad crew member transitioned from the pressurized interior of the ship to the vacuum of space, all the crazy exploding battle sounds stopped. It made for a very clear contrast, emphasizing how hectic the inside of the ship was.

Another interesting example of sound in space was the climactic explosion of the Nostromo in Alien. Although there was sound in that scene, the sound was reasonable, given the situation. A nice ballpark amount of atmosphere needed to carry sound is that on the surface of Mars (about 1% of Earth's). Using that as a benchmark, the vaporized ship would have provided an envelope of sound approximately 15 km in radius.

Finally, if external ship sounds are necessary for the story, take a page from the movie Event Horizon. The entire film took place in the upper atmosphere of Uranus. Not only are there most of the hazards and issues of being in space, but there is also some nice creepy clouds, lightning, and most importantly, sound.

It is absolutely beyond me why movie makers continue to insist that sound in space is required by audiences. There's no dramatic reason for it that couldn't be accomplished in a more realistic manner. For most scenes, an accurate portrayal would help to highlight the stark unfamiliarity of space. Hopefully more people will be like Joss in the future.

Tuesday, September 29, 2009

Physics: It's not a Game (Gamer)

I recently saw a movie which reminded me why I'm doing this. The movie was Gamer. This was a pretty bad movie, but the biggest problem it had was a very serious tendency to ignore the laws of physics when it comes to certain objects. Most notably amongst these was Newton's Third Law of motion, and bullets.

Newton's Third Law is a very simply stated law: For each action there is an equal and opposite reaction. What this means is that if something is pushed on, that thing will push back on the thing doing the pushing just as hard as it is being pushed on. Overall this is a very positive thing. I imagine it would be problematic if an object pushed on the ground, but it only pushed back with half of the force. The ground would be unable to support the object, and it would sink! There are other consequences of the Third Law however. The problem is, this applies to any object feeling force, including a bullet being fired out of a gun. The bullet feels a large force as it is accelerated down the barrel of the gun, this force is then transferred through the firearm to the person holding the weapon. Which brings us back to Gamer.

In Gamer, there is a scene where the main character is attempting to rescue his lady from her job. There are people chasing him, and one of these people corners him in front of a doorway. The villain fires a gun at him, and he is propelled back with enough force that he is first knocked off his feet, then destroys the door behind him. Despite his rather epic flight through the door, the man who fired the gun barely had to brace it and recovered almost instantly to grab the lady. There are all kinds of things wrong with this scene, but we'll take them one at a time.

All of the problems stem from one thing: bullets aren't very massive objects, and people are. To propel a person back a projectile requires a lot of momentum, and the only way a bullet has that kind of momentum is if it's going very very fast. Normally a bullet going very fast wouldn't be stopped by a person, but the hero was wearing body armor, so it's assumed that the bullet transferred all it's momentum to the hero. So the question is, how fast would a bullet have to be going to pack enough momentum to throw a person back. It turns out that the equation is very simple:
Mass of the bullet multiplied by the speed of the bullet has to be equal to the mass of the person and bullet together multiplied by the speed of the bullet and person together, after the impact. This can be represented by:
Mbullet*Vbullet = Mboth*Vboth
So, by filling in the rest of the variables, the speed of the bullet before it hits the hero is known. First, assume that the hero flew back at 5 meters per second, or about 11 miles per hour. Since he was knocked off his feet and through a door, this might be on the slow side, but it will work well enough for our purposes. Then assume that, being a large man, he massed about 100 kg. Next, we need a mass for the bullet. Since a NATO standard 7.62mm round masses .01kg we can take that to be a fairly close approximation of the bullet used. Solving for the speed of the bullet we get that it would have to have been going 50 kilometers per second, or 112,000 miles per hour. This number is roughly 4.5 times the speed required to shoot and object into space and have it never come back. Now, there are objects which travel at this magnitude of speed which people see all the time, they are meteors, tiny bits of rock which occasionally fall through the atmosphere. The thing is, most meteors are very small, and at these speeds even sand grain sized meteors are visible from the ground, 50-60 miles away! So, imagine something that's emitting as much light as a bright meteor, but is only several feet away. Catching on fire due to the intense heat and being blinded by the light would be larger problems than just getting shot at.

Now that the bullet speed is known, it's time to take a look at the effect this would have on the person. The problem here is that the gun had to push the bullet up to that speed, so one of two things should have happened. Either the man holding the gun should have been thrown back at the same speed that the person hit with the round was, or (and this is much more likely) the gun would be ripped from his hands and hurled back itself. If the gun massed about the same as and M16, it would have been hurled backwards at 320 miles per hour.

The worst part about all of this is that the scene could have been easily achieved without the use of the impossible bullets. An explosive device planted in the elevator would have the same effect of being surprising and knocking the protagonist back, but it wouldn't have required breaking the laws of physics to achieve. So lets leave the really high speed stuff to meteors and keep bullets in the realm of the reasonable. It's odd though, in the scene just after the one discussed, they had a very interesting Newton's Cradle, kinda like this one, only full of scantily clad women:
Odd how you can have such a good example of physics in a movie next to a complete lack of it.

Tuesday, September 22, 2009

Asteroid Belt: Not as Dense as Advertised

This is a scene that is repeated over and over again in movies, books, games and any other area where science fiction has a place. Our protagonists are in a ship, it's being pursued hotly by some alien doom vessel trying to destroy them, and their only chance at escape/survival is to dive into the asteroid belt and hope that the alien pilot can't keep up with the many collisions and flying rocks! Basically, flying through a scene that looks very much like this:

This scene has one very large mistake in it: space is very, very big. There are two consequences of this; the first is that it is unlikely that one will find an entire asteroid belt that is full enough of rocks to have this scene at all, but there will be more on this later. The second consequence is that most space flight "chases" are going to be taking place with the ships light seconds apart, with the chasing ship firing, and then waiting to see if the shot hit or not. There is a small subset of people who might enjoy that type of scene, and this is the type of person who likes submarine thrillers; who waits on pins and needles to see if the shot fired hits and if the ship was detected soon enough for the enemy to get their own firing solution. But for most people, having 20 minutes of movie waiting to detect an explosion five light minutes away would be pretty boring.

The truth of the matter is, although the asteroid belt is a comparatively densely packed part of space, there just aren't that many rocks in there. The entire asteroid belt of our solar system is only 4% the mass of the Earth's moon! Even more interesting, more than half of the total mass is contained in the four largest asteroids. What this means is that a spacecraft is not very likely to find an asteroid, let alone have to dodge around one. According to Alan Stern of Space Daily, there is a less than 1 in 1,000,000,000 (billion) chance that a ballistic trajectory satellite would hit even one of them when passing through the asteroid belt. To give some perspective on the amount of rock this is, if one were to smash up all the rocky planets in the solar system and place them in the asteroid belt, there would be 10,000 times as much rock as is in the belt right now. This would only bring a ship up to a 1 in 100,000, chance of hitting something when passing through the asteroid belts, assuming that the size distribution was similar to what it is now, and that the ship doesn't dodge. So, the odds of hitting a rock in the asteroid belt with a ballistic ship are similar to the odds of throwing a rock in the ocean and randomly hitting a whale. This would seem to be an unreasonable amount of rocky material to have in a single system. Real asteroid belts are hard to tell apart from the rest of the system from the inside.

So, the moral here is that if a chase scene of this type is needed, have it be near a planet. Maybe a moon broke up, maybe they've been dragging rocks nearby for mining purposes, maybe the planet just has unusually thick rings. But having an entire asteroid belt this dense is over the top.

Tuesday, September 8, 2009

Dragon*Con Photos

Here are all our Dragon*Con photos and these are from our Roomate. If you got to this site because I gave you a card, try to find yourself, and have a look at my site! Science Advising will continue later this month.

Friday, September 4, 2009

Dragon*Con Awesomeness

Hello to everyone who found this site because you got a random business card at Dragon*Con. If you don't need any science advising, please feel free to check out the site and see if anything amuses you. If you do, feel free to follow the email link and contact me. Also, I am going to be posting all the pictures I took at Dragon*Con for all to look at, so if you want to see yourself in your awesome costume, come and check it out!

Awesomeness Quotient

This is sort of general advice for anybody making anything science fiction. The degree to which you can get away with something that is scientifically unsound is proportional to how much more awesome it is than what real science would allow. In other words, if you have a plot device which requires bad science to exist, take a look at what real science would allow. If your device is much, much cooler than the real science, and isn't too unreasonable, you're probably good.

This can be represented by a simple formula:

Allowability = (Plot Device Awesome - Real Science Aweseome)/ Badness of the science

What this boils down to is, if your plot device is very awesome, and your science isn't too bad go for it. If, on the other hand, your plot device is kinda underwhelming, and/or the amount of bad science required to realize it is very high, then probably come up with a different plot device.

I'll give an example of each so you can see what I'm talking about. Let's start out with the bad science that doesn't in any way contribute to the story. What we are going to use is one of the worst science movies of all time, Mission to Mars. The scene which is the most guilty of this is the scene where the astronauts are transferring from their damaged space craft to an orbiting supply ship. Tim Robbins' character overshot the supply ship and was drifting off into space. His wife sets up her suit to use half of its fuel to try to thrust out to him and save him. Right there we have our problem. If you use half your fuel to thrust away from something in space, it takes the other half to stop. What they did was allow her to thrust away from the ship and then magically stop in space for her to be able to turn around and live! Let's try running this through our equation.

(Bad plot device - Both of them die ending the movie sooner!)/Terrible Scene = Shouldn't have been used.

Now, to help us feel better, let's give an example of a really good scene. The new Star Trek movie, love it or hate it, this movie had good science. Now, if you've seen this movie, you're probably wondering what I found to pick on. I admit, I didn't find this, it was pointed out to me by the most excellent Phil Plait. There was a scene where the Enterprise was coming up out of Titan's atmosphere to to ambush the Romulans. I know what you are thinking, this scene had some great science, Titan's atmosphere was the correct color, the Saturn images looked straight out of Cassini, what's the problem? Answer, Titan's orbit is in the same plane as the rings, you wouldn't be able to see them from Titan. However, let's just run that through the equation for this scene:

(Awesome view of Saturn's rings - Not seeing Saturn's rings)/Awesome Dramatic Scene = Must include in movie.

So, as you can see, even if the science is a little bad, you can use it in movies. Just try not to make the science types out there cringe.

Sunday, July 26, 2009

Iron Giants Want Science Too (Spoilers)

The other day I was watching The Iron Giant. Now, this is basically a family movie about a giant robot from space that lands on earth and is damaged so it can't remember its purpose. This movie is overall a fantasy, and it doesn't worry me too much when it does odd things like have the robot eat metal. There was one thing that was bad enough to throw me a bit, and that was when the Robot heroically saves the town from the nuclear weapon at the end. Overall, I quite liked this scene, it showed the basic insanity of what was going on, and the self sacrifice was a nice touch, and I tend to think they did a very good job with it. It does bring to light one slight misunderstanding people have about how nuclear bombs work. Unlike conventional explosives, nuclear bombs won't be set off by an impact event as was shown in the movie.

In general, there are two types of fission warheads. The first type of warhead is what's called a gun-type warhead; basically you have two slugs without enough mass to go critical, but when brought together go supercritical and you get a large explosion. This type of nuclear bomb would, in fact, detonate just as was depicted in the movie. The other type of nuclear warhead is what is called an implosion type nuclear warhead. It uses much less fissile material, and instead has a series of explosive lenses which, when detonated very precisely, cause the fissile material to compress and go supercritical producing a nuclear blast. By 1957 the United States had switched to using almost entirely compression style nuclear warheads due to the fact that they use less fissile material, and are much safer to operate. Further, I was unable to find a single instance of the United States using a gun type warhead in a nuclear missile, they were only put into gravity bombs. Crashing into the side of one would almost certainly destroy the explosive lenses and prevent a supercritical explosion.

So, what does this mean for The Iron Giant and other movies of its type? The giant might have been blown apart when it destroyed the warhead due to the small explosions of the lenses inside the warhead, but there would not have been a nuclear blast as depicted. This is, admittedly, a very minor nitpick, but it was severe enough to pull me out of the story when it happened, so I thought it was worth mentioning. The Iron Giant was an excellent movie though, and I recommend you watch it if you haven't.

Thursday, July 9, 2009

Speed Racer can really really go! (Oh Spoilers!)

I recently watched the film Speed Racer by the Wachowski brothers. Imagine my surprise that I really enjoyed the film! Overall, I think that the stunning visuals and bright colors, coupled with good to excellent acting force me to give this movie a bit of a pass as far as physics goes. But there was one scene that made me wonder if, even given the magical properties of car and driver, would be possible.

The scene in question takes place during a cross country race, which Speed has engaged in so that he might help the government with some investigations. At one point during the race, Speed's car is forced off the track! Not one to be stopped by a little setback like being forced down a cliff, he drives his car back up a nearly sheer cliff face! The question is, could even the Mach 5 have been able to achieve such a feat?

The answer should be no, probably not, but that would be boring. To find this answer though, we need to know two things. One, what is the primary force driving the car, and the second, what is the maximum force output that it's capable of. The answer to both questions can be found in how the car drives around normal turns.

In the movie, they state that the speed of the vehicles driving around the track is "800 km/h." We'll assume that this is a high end as we use this number to allow us to approximate the speed at which he goes around the turns. I'll guess he's going about half his maximum speed when taking the tight hairpin turns. If we assume that the Mach 5 can take a 10 meter radius turn at about 400 km/h, which is reasonable given what we see, then what would the acceleration be to keep him in the turn? Using the equation V^2/r, you find that the centripetal acceleration would be on the order of 200g. Notwithstanding that no human could survive that level of acceleration, this would at least be possible given a car made out of unobtainium and some magical drive system. It does tell us one important thing though: the primary motive system for the car is not the motors driving the wheels, but the thruster at the back of the car. To see why this is you need only look at how tires function. Tires rely on frictional forces between themselves and the road to provide the force on the car. The equation that describes this force is mu*normal force * gravity, where the normal force is the weight of the car and mu is what is known as the coefficient of friction. To provide the 200g's required, mu would have to be equal to 200, since the highest coefficient of friction that I could find was gecko feet, at 8, we can safely assume that this number is ridiculous. Now that we have all this, we can discuss the mountain climb.

We can see clearly in this scene that the mountain is not a sheer cliff, so there would be some small force holding his wheels to the ice. Combined with the spikes on his tires, this might be enough grip to allow him to control his ascent. Now, given that the nominal acceleration of the Mach 5 is 200g, minus 1g of gravity, he can not only drive up the cliff, but drive up it at 199g. Although the overall physics of this movie is silly with respect to the car, if you give them the Mach 5, the rest is surprisingly consistent. Well done, Wachowski's.

Sunday, June 21, 2009

Death Race (Standard Spoiler Warning)

The movie Death Race has some great scenes of cars driving around a track on a prison island, firing weapons at each other, and generally doing awesome things. Many of the events in this movie are rather difficult to critique, as no details were given for most of the cars. This was a good thing as it allows audiences to enjoy the movie without the pickier people getting upset. Though, there were two particular scenes that would make even the most casual of science conscious persons cringe.

Both scenes are caused by the same plot device, which is a modification to the main character's, Frankenstein's, car. Frankenstein's car is a Ford Mustang fastback which has been heavily modified. The car is armored on all sides, and has both offensive and defensive weaponry. Although we have to speculate about some of the modifications and the performance specs, the car would mass in at about 4577 kg. The bulk of the extra weight comes from a defensive shield installed on the back of the car called the Tombstone. Using images from the movie it appears to be made of 4 plates of steel, getting wider as they reach the car. Each plate is about 2 inches thick, with the narrowest plate being 27 inches wide and 40 inches tall, and each plate closer to the car being 12 inches wider than the preceding plate. This gives the shield a maximum thickness of 8 inches at the center and a mass of 1855 kg using 7.85 g/cm^3 as the density. In the movie the stated thickness of the Tombstone was 6 inches, but with the varying thickness, we'll assume they meant that as an average thickness. The suspension of the car would have to be designed to handle this kind of weight, so we can assume that the spring constant for the rear suspension must be on the order of 1250 lbs per inch. The car in this configuration performs such that all the cars on the track have approximately the same handling and acceleration profiles.

At two points in the movie, the Mustang has to drop the Tombstone off of the back of the car for various plot related reasons. In and of itself this seems like a very good idea. 1855kg of steel flying back at the car behind you would certainly cramp his style, plus your car is now lighter, but in the movie there was no measurable difference in the performance of the car from before the Tombstone was dropped to after.

There are two major effects that would happen from dropping this large of a mass off of a car. The first is that the rear suspension would be heavily unloaded. Since the suspension was balanced for having an extra 1855 kg hanging off the back end, removing that would cause it to very quickly unload. If we assume that the car was designed with about 4 inches of droop on the rear suspension, then dropping the rear plate would cause that to decrease to less than one inch, and it would be almost impossible for the suspension to work in turns or over dips in the road. This would first cause some bouncing when you first unloaded it, potentially causing a loss of control, and would then cause your rear end to hop around the turns. It's possible that Frank 1 and 2 were both good enough drivers to compensate for the hop, but there should have at least been the initial bounce.

The second is that the car would now be lighter. Much much lighter. If you use the number that we assumed for the car's mass, dropping the Tombstone off of the back would decrease the mass from 4577 kg to a mere 2722kg! This is a 45% decrease in the total mass of the car. As we know, Force = Mass * Acceleration. Since the engine is putting out the same amount of force, if you could still put the power to the ground you would expect a 45% increase in acceleration. To put this into perspective, if we make the reasonable assumption that the car went from zero to sixty in 6 seconds as set up before dropping the Tombstone, the new zero to sixty speed would be 3.57 seconds! Even if we assume that he wouldn't be able to put the power to the ground via the wheels quite as efficiently, he should still have a marked improvement in acceleration over the other cars on the track which haven't dropped 1855kg off the mass of their car, but they pretty clearly keep up with Frank despite his last ditch emergency efforts.

The movie was fun, but they could have easily shown these effects on the car without changing the story in any way, and there would have been a much lower cringe factor for the car conscious in the audience. After all, they are the most likely to watch this kind of movie.

Tuesday, June 9, 2009

Unwanted, or, How Not To Run Down A Hall(minimal spoilers)

In the beginning of the movie Wanted, there is an epic scene where some nameless man in a business suit is trying to get a bullet identified. Just before he can get anymore information out of his contact, assassins on the building across the street open fire on the office, killing his contact, but missing him. He runs down the hall away from the office, seemingly to escape the gunfire. When he reaches the end of the hallway though, he turns around, gauges the distance, opens the elevator door to give him a longer acceleration distance and starts sprinting down the hallway with so much force he dents the wall of the elevator. Papers are flying and people around are being blown back by his wake. He smashes through the plate glass window in the office, flies across the gap between the buildings, shooting three of the assassins on the other roof, and then crashes into the next floor down. A very epic scene, but is it reasonable?

The first thing we need to determine are the approximate distances involved: how long was the hallway, what was the gap between the buildings, and how far did he drop. The length of the hallway can be determined using the distance between doors in the hall and then counting doors. We'll approximate the width of the office as being typical for an office, about 5 meters, and the elevator as being 2 meters wide, giving us a total acceleration distance of 21 meters. To determine the distance between the buildings, we'll use the top down view of his jump as a reference. There appears to be 8 lanes of traffic and 2 sidewalks between the window he starts from and the one he crashes into. Using the national highway standard for minimum lane width of 12 feet, and seeing that the sidewalk was somewhat wider than the lanes or about 15 feet, he would have to cover a gap of 126 feet, or about 38 meters. Using the height of 6 feet for the assassins you can approximate the distance down to the window he enters the building through. You find that he dropped around 6 meters. So he accelerated over 21 meters, burst through a plate glass window and cleared a 38 meter drop falling only 6 meters. That's quite the jump. Now we'll take a look at the physics.

First off, how fast would he have to be going to make the leap across the building gap? Since he fell 6 meters, using some basic kinematics and ignoring wind resistance, we get that he would have to cover the gap in 1.1 seconds in order to only drop 6 meters. Since the gap was 38 meters, that give us a speed of 34.5 meters per second, or 77 miles per hour! Needless to say, this is unreasonably fast for a person to run and still be called human. The bigger problem though, is what kind of energy would he have to burn to reach this speed? If we assume that he has a constant acceleration down the hall, we get that over the hall's length, he would have to be accelerating at 28.34 meters per second squared to have achieved his required speed by the time he hit the window, assuming the window didn't slow him down at all. To achieve this kind of acceleration the guy would have to be putting out 59 HP! To put this into some perspective, this would require that he metabolize just over 3.2 grams of sugar, using 2.7 litres of oxygen just in the ~1.2 second run down the hall! In other words, he's putting out about the same amount of power as a 1967 Volkswagen bug's peak horsepower. This may not seem like much, but this is also 44 times the peak power output generated by Lance Armstrong while riding in the Tour De France in 2007. You would exhaust your body's sugar reserves, on average, in less than 3 seconds with that kind of output. It just doesn't make sense.

Overall, I liked the scene, and I say you could keep it, but maybe put the buildings 15 meters apart instead of 38? At least that way you end up with numbers that a human being might possibly accomplish!

Tuesday, May 19, 2009

Sunshine is very cold! (Spoilers Ahead)

Sunshine was a movie made in 2007 by director Danny Boyle. Overall the science in this movie wasn't terrible. There was one scene, however, that made me cringe.

(begin minimal spoilers)

About 1 hour into the movie, several crew members get stuck on a second ship which has had the airlock blown out. There is only one space suit, and no other way to return to the main ship, or pressurize the airlock area once the seal has been breached. They come up with an idea to try to get as many crew as possible back to the other ship. They put one crew member in the suit and have the others wrap themselves up tightly in insulating fabric, then they tie themselves onto the suited member. Using the gas pressure from the damaged ship when the airlock is blown, they will rocket across to the other ships airlock and live. So far, this is very good. The gas would expel you across the gap pretty quickly, and it's possible that you could survive a very short exposure to hard vacuum. Further, the tight wrapped insulating material would help protect you from the vacuum to a certain extent.

The problems occur shortly before they launch from the airlock. The crew members who remained on the main ship inform them that they will have "20 meters to cover at -273 degrees Celsius". Although this temperature would be more accurate for deep space than this close to a star, since they are behind a solar shield and would be likely to round the temperature to the nearest whole number, -273 Celcius is a reasonable temperature. After wrapping themselves up in insulating material torn from the walls of the ship, they blow open the airlock and start to shoot across the gap. Oh no, one of the crew members got knocked off a strait trajectory and has drifted off into space unable to be rescued. At this point, due to the great cold of space, he quickly freezes into a astronaut-sicle. Wait, is that right? Freezing in about 1 minute is what you would expect in an atmosphere at that temperature, but what about space?

In space, temperature doesn't mean the same thing that it does on earth. When you are in an atmosphere, the temperature has to do with the thermal energy possessed by the air. It turns out that in air, Newton's law of cooling describes the rate at which things cool fairly accurately. The rate of change of thermal energy equals the heat transfer coefficient of your medium times the area of your object times the difference in temperatures. For air, the heat transfer coefficient is between 10 and 100 watts/meter^2 kelvin. So, for very large temperature differences, this will cause you to cool very quickly, linearly increasing as the difference decreases. In space, a much different process occurs. It turns out that radiative heat transfer is proportional to the difference between the 4th power of the temperatures (body^4 - ambient^4), which would be very fast, but the constants on the front are very tiny. Specifically, a given object with an identical temperature difference would cool 6 to 60 times faster, depending on atmospheric composition, in an atmosphere as compared to in a vacuum. That gap will widen very quickly, since in a vacuum the loss rate changes proportionally to the temperature to the 4th power. If you do the math, using the approximation that a human is a sphere with a surface area of 1.81 meters, an emissivity of 1, and a mass of 80kg of water, you get that after 1 minute the temperature of his body would only have dropped to 308K, from 310K, which is well above the freezing point of water. In fact, it would take more like 45 minutes to even reach freezing. So, that scene, although very dramatic and cool, was kind of silly. I admit though, the much more realistic thing to have happen would be some nasty things coming out of all your orifices, and it would be much more disgusting than what they chose to portray.

Go rent Sunshine though, it's a very pretty and thrilling movie!

Edit: New exciting information! It turns out that according to the FAA and NASA, you won't actually be able to stay conscious very long if exposed to hard vacuum like that. The amount of time that you retain useful consciousness in rapid decompression situations would be on the order of 5-10 seconds if you were breathing normal air before the decompression. What this means is that it is unlikely that the unsuited crew members would have been able to act in any way once exposed to space. Further, the damage taken would be so extreme that they would need immediate medical attention to survive and would in no way be active after exposure to space. This scene gets less plausible as I learn more.

Wednesday, May 6, 2009

Science advised?

Watch the video above, and then read below.

I have just watched the first 6:38 minutes of Vertical Limit. I was thinking that I would do this in a sort of narrative, where I explain what's happening in the movie, and then pause when they get something wrong, but they got too many things wrong. Since I found 24 things, I think I'll just list them one by one.

1. In the first scene of the movie, there is an eagle swooping around near a mesa. During one scene you can clearly see the eagles legs dangling down towards the ground. Now I'm no ornithologist, but I'm almost totally certain birds don't fly like that. The scene looks CG , and I think they may have missed a bit. Any ornithologists can email me, and I'll get up the correct information.

2. During the entire scene, you can clearly hear their voices echoing as if off the walls of a canyon. This seems reasonable on the surface, they are near a rock wall...echoes! But in reality this is a little bit odd. If they were climbing the wall of a canyon, you could expect to hear echoes, but on the face of a mesa like they were climbing on, there would be nothing to have the echo bounce off of. Probably, it would have sounded more like if you were standing next to the second story of a house in the middle of a big open field. One slight echo, and nothing else.

3. Another problem in this scene is the way they used anchoring. The first instance of this is the crack which the girl has placed three cams in. The only serious problem I see is that it appears the crack is increasing in size as it goes down, which would seem to cause some problems in the event that any force should be applied down on it. Overall, I think this was a bad protection setup.

4. This is a minor nitpick, and may have just been something that they did off screen because it wasn't considered important to the plot, but the girl never once secures her carabiner locks, or checks them for having locked. Bad practice if nothing else, but they have bigger problems.

5. Shortly after the scene with the three cams in the wall, the young male character is seen jumping up to one high section of the wall. Apparently they didn't build the sound stage to the same dimensions as the rock wall they used for filming, because although in one scene the climber is shown feet dangling, in the next he is easily bracing against the wall below him. Just sloppy really.

6. This was another thing that struck me as quite odd. The girl is clearly using cams in a crack in front of her as an anchor for her and her brother and father. Although this in and of itself isn't very odd, everywhere else on the wall they used pitons, a sort of nail system where you pound an iron spike into the rock that has a hole to put a carabiner through. These are effective, if usually illegal. I'm not really clear on why you'd use a more secure type of anchor everywhere but your main anchor.

7. If you carefully watch the girl on belay (belaying explained in number 18), you can see that she isn't backing up her automatic locking belay system with a strictly physical system. This is also a bad practice. Should the boy fall, and the automatic stop fail, he would likely plummet to his doom, almost a minute earlier than he would otherwise.

8. Just before the real insanity starts, there is a pack dropped from high above them. The pack falls past them with the rope trailing. Depending on what was in the pack, this might actually be reasonable. Climbing rope is fairly dense stuff, and would tend towards overcoming air resistance quite well, but the pack could be full of water, or cooking supplies, or lead weights. The bigger problem is that the pack seemed to be falling at terminal velocity. Although it's possible that it would have reached its max velocity in the time shown, it's very unlikely.

9. Right here is the first time that the physics of the situation gets really out of hand. One of the inexperienced climbers high up on the rock face slips and falls off of the rock. Normally this wouldn't be a big deal, but his piton anchor fails as he falls. But there's the problem: the anchor fails before he even puts weight on it. In a real situation, if his protection were to fail, it would be most likely to do so when he was at the bottom of his fall, where the tension was at the greatest, not when he was at the top, where there would have been no tension on it at all.

10. The next problem is another problem with anchor tension, but this time on the opposite side of the swing. The climber falls down, but has a second anchor which stops him from immediately falling to his doom. Since it's tied to the wall and to the second climber, he swings in a long arc, almost another climber further down the wall, and then swings back up to the level of his climbing partner. This is the point when the anchor fails. Not when it was under the maximum strain at the bottom of his arc, but afterward when it was once again under almost no stress at all. It's very odd that these climbing protections keep failing when there's no strain and holding when the strain is greatest.

11. One thing that I found a bit odd was the relative speeds of the falls, as mentioned earlier when a pack was dropped from the people higher up on the wall. The pack, when it falls past them, appears to be roughly in the steady state, with no acceleration, and the fall is quite fast. The two people who fall later however take almost 3 seconds to reach the height of the climber closest to them. Either the people are much less dense than the pack, which is possible if the pack was filled with lead weights as discussed, but not likely. Why they didn't just film packs being dropped off of a cliff, I have no idea.

12. Okay, this isn't a problem in and of itself, but it sets us up for some of the later problems. When the people fall off of the wall, they are accelerating at the earth standard of 9.8 m/s^2. With this acceleration, it takes them 3 seconds from when the 2 of them are off the wall, to when the father is pulled off of the wall. After 3 seconds of acceleration, they would be going 29.4 meters per second, or about 65 miles per hour. This certainly makes it reasonable that the lower climbers and most of their anchors would be pulled off of the wall, a person going 65 miles per hour has quite a bit off momentum!

13. At this point we see the falling climbers pull two more climbers and two more anchors off of the wall. This is reasonable since they are carrying quite a bit of momentum, but their fall is arrested by reaching the end of the trio of experienced climbers' ropes, and being wrapped around the father. How, though, did the last set of anchors hold when the first two were ripped out of the wall without even slowing them down? The breaking strain of a piton is on the order of 15000 newtons. Since these snapped quite fast, we can assume that these had much higher forces applied to them, but the cams which she used for the final anchor which held have an approximate breaking strain of 14000 newtons. If you assume that the climbers were in free fall until the end of the rope. reaching a speed of 50 meters per second, and that the rope stopped the fall in about .2 seconds, there should have been upwards of 40000 newtons being applied to the cams just from the first two climbers, not including the father and son, which would have broken them handily. This is the fist point at which everyone would have died.

14. The next problem we have is the problem of the father stopping the falling climbers with his midsection. Using the numbers from above, there were 40000 newtons being applied to his midsection. If we assume a climbing rope has a 1cm contact width and that his waist was about 45cm of contact length, he must have had a pressure on his waist of approximately 8 million pascals. Since the breaking pressure of muscle is on the order of 500,000 pascals, it's safe to assume that the rope would have, if not cutting him in half, at least have delivered fatal injuries to his internal organs and spine, making falling down a bit of a moot point.

15. After the impossible stop that would have ended all their lives, and the force which almost certainly would have killed the father, there was yet another force which would have ruined his, otherwise, perfectly good day. After several seconds of being calm and trying to keep things together, the father slips and the rope which was around his waist slips past his neck and off of him, killing the first two climbers. Your neck is not a free interface though, according to the internet, it takes on the order of several hundred newtons to break someones neck, and the climbers appeared to weight more like 1000 newtons. As the rope slid past his neck, he would have, at the very least, had his trachea crushed, making it impossible for him to talk or breath, and at the worst a broken neck. So, the father is now dead 3 times over.

16. After the people fall, there is some discussion about how the anchors don't have the strength to hold all three of them. This is odd as they survived a 40000+ newton fall, but now only have to hold something on the order of 1200 newtons static. Also, since these anchors are specifically designed to hold up to these forces it is unlikely that even one would fail after the initial fall, let alone all three that she placed.

17. Something interesting I noticed was the fact that they were hanging very far away from the wall. The girl was trying to reanchor them in, but couldn't reach. There was a shot earlier though that clearly showed the section of rock which was underneath them had a gentle slope, which is kind of the opposite of an overhang. If anything they should have just hit the wall quite hard.

18. Now that they are hanging free though, we see another large physics blunder. The climbing system basically works by having one person on belay, who serves as an anchor, and another person climbing. Ideally there is a top anchor which has a pulley so that if one person falls the other person's weight is used to stop them. Since there is a pulley at the top, a much lighter person could belay for someone. However, in this scene we see the small girl being a stable counter for 2 grown men. Even with the pulley, she wouldn't have enough weight to balance it, and should have been pulled up to the top of the belay system instead of hanging stably.

19. The next blunder is that after the girl is unable to reach the wall to anchor them back in, the father tells his son to cut to rope, thus reducing the weight and saving his kids. The son pulls out a strait bladed knife to try to cut the rope. This would be fine if he had quite a while, but this type of knife was not designed to cut ropes. It would have taken quite a while for him to cut it even after he decided too. Much more likely for a climber to be carrying would be a serrated edge, which would be much faster at cutting that type of tensioned rope. I'll post a video about this later!

20. The next problem would have occurred just after cutting the rope. Although it may not seem like it at casual glance, climbing rope is actually a very stiff spring. This give is what allows you to fall any distance without breaking anything when the rope stops you. If it wasn't springy like this, the stop from the rope would be just as bad as hitting the ground from the same height you fell from. Now the problem is what happens when you partially unload a spring? The spring begins to bounce. The oscillations will be quickly damped in a climbing rope, but they will be there, and the bounce would have easily been enough to pull the last anchor from the wall, in fact, much more likely to do it than the weight of a third person.

21. This last one is a bit speculative, and they likely did it to keep the rating down, but the end of this 6:38 seconds of pain is a shot of the fathers body hitting the ground. When a person would hit the ground at the speed he hit, landing on solid rock, it's more likely that he would splash than bounce. A person's body simply couldn't maintain structural integrity if it hit like that. Would have been quite gross, I suspect.

Okay, that's all I could find in the first 6:38 minutes of Vertical Limit. I guess it was actually quite a bit. Between all the breaking and falling, that was really quite bad. Now, I suspect you'll have noticed I didn't really suggest any changes, that's because this scene was a total loss from go, more or less. A much better scene might have been to film a real climbing scene with real climbers where a reasonable single piece of equipment fails(say a carabiner) for the kid to blame himself for. At least you wouldn't have to violate the laws of physics.

P.S. The new swish logo courtesy of Roy! Go check out our blog Darktaco.

Thursday, April 30, 2009

Sneak Preview

Alright, I don't have time to do the breakdown of a couple of key scenes in this movie yet, but the first movie I'm going to critique is...Vertical Limit!

Wednesday, April 29, 2009

Welcom to Science Adviser Blog

Welcome to the Science Adviser Blog. The purpose of this blog is to look at movies in excruciating detail, pointing out the good and bad science of given scenes, and then making my suggestions as to how I would have done it differently. If you find it interesting, have suggestions, or need a science adviser for something creative, feel free to contact me. Enjoy.