I finally saw the movie WALL-E. Good flick, I liked it. There was, however, one part I must comment on. You know I can't help myself. I feel like the shark Bruce in Finding Nemo. I try not to attack, but there is a tiny drop of blood in the water. Here is the scene that I want to talk about:
I guess I should give a spoiler alert. Although, I will not talk about the plot of the movie.
In this scene, WALL-E is hitching a ride on this space craft. The space craft is entering a hanger deck of a space station. While the hanger door is still open, WALL-E is clearly hanging on so that he won't float away (no gravity or maybe everything is in orbit around a planet). As soon as the door shuts and possibly the hanger becomes pressurized, WALL-E falls off the top of the space craft suggesting that there is some type of gravitational force.
Yes, the people in the movie clearly have advanced technology. However, the scene seems to agree with the common idea that if there is no air, there is no gravity. What you say? Really? Yes, this is really a common idea. You can see this idea when you ask people why astronauts are weightless in orbit. Some will say it is because the astronauts are beyond the atmosphere where there is no gravity. I talked about what causes astronauts to float around in a previous post. It is not a lack of gravity.
This idea about gravity and air can also be seen when talking about the moon. It is not uncommon for people to say that there is no gravity on the moon because there is no air on the moon. Of course this is wrong for a couple of reasons. First being that there IS gravity on the moon. If you ask a person how astronauts walk on the moon if there is no gravity, the answer is "heavy boots". I saw this somewhere on the internets, but I didn't believe it until I actually got these answers from students. Heavy boots trumps no gravity.
Ok, I know I will get a comment.
There, I beat you to it. And since someone is going to get upset anyway (remember, I said I liked the movie), I will point out one more thing in WALL-E. Here is a shot from the scene where the space craft is leaving Earth:
In this scene, the spacecraft has to break through all the Earth-based space debris. The first problem is that the unused satellites are just sitting there. If they were to stay in orbit, they must move. Maybe the WALL-E creators are sticking with the no air means no gravity idea. At least they are consistent.
The other problem with that scene is the sheer amount of junk in orbit. Suppose that was 300 km above the surface of the Earth (the orbital distance of the space shuttle). What is the volume of of this space (say it is 100 meters thick - which is tiny). The volume of this shell would be:
Where r1 is the radius of the Earth plus 300 km = 6.678 x 10 6 meters and r2 is 100 meters more. This gives a volume of 5.6 x 1016 m3. See - that is a lot of space. How many pieces of junk could fit in this? Let me give an overly large estimate that each piece of junk gets (on average) a cube of 100 m x 100 m x 100 m (1 x 106 m3). How many pieces of junk would there be? Well, I can just take the amount of space available divided by the space for each piece of junk and I get: 5.6 x 1010 pieces. If Earth launched one spacecraft a day, that would take 153 THOUSAND years. Just saying.
Here is the real question I had during the movie (and I don't know the answer) oh wait.....
This question may give away more on the plot. Anyway, I tried to warn you. In movie, there is a large space craft that is essentially maintained by robots for more than 700 years. The humans don't really do anything. The question is, if there is an energy source, is it possible for robots to maintain order in such a way forever? Would this violate any laws of thermodynamics? Is it possible to build some robots that are able to continue repairing themselves and cleaning stuff forever? I don't know.
