Concave mirror (from movie)

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Ortix

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Hi everyone, hopefully this is the right forum i'm posting in.

To keep things short: I'm doing a physics project as a final exam in my physics class. We have to pick a movie and find the bad physics in it.

I decided to do sunshine and found some interesting things.

However a couple of things are bothering me regarding the shield

First of all, After seperation of the payload (only for those who have seen the movie) looks WAY to small to protect the crew for the return trip.

Second, that small shield looks like a concave mirror (if it's facing the sun) with the ship attached to the back. No, as Cappa is flying towards the payload, you can clearly see some of the light reflecting off the shield.

http://img269.imageshack.us/img269/7184/concave.jpg

Is this possible? I mean, isn't the light supposed to fry him in the first place because an image is formed at the focal point? On top of that, for some reason i think that if light hits the shield, it should not hit it on the edge first but in the center, or am i wrong here?

Could someone clarify this for me? Thanks!

R

rogerinnh

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The reflective surface of that spaceship is convex (like the outside of a bowl) not concave (like the inside of a bowl). The picture you show seems to show the astronaut BEHIND the spacecraft. Light refelected off of the reflecting surface of the spaceship would not form a focal point.

As I recall from the movie, the ship is temporarily positioned so that the astronaut can go to the reflective side and repair a part of the shield. He gets fried as soon as he enters a non-shielded area. That is, there is no focusing needed, the enormous intensity of the sunlight fries him.

One thing that I thought was odd about the movie is that the reflective shield is made up of an enormous array of movable panels. And it's when one of those panels loses its ability to be moved that they run into problems, requiring the astronaut to go out and repair it and in the process get toasted. I just wonder why that shield has to have movable panels. Why isn't it just one huge solid surface? In order to protect the cargo you simply keep the shield always pointed towards the sun. There should be no need to have separately angled panels on it.

M

MeteorWayne

Guest
This does not belong in Physics. I will move it to SciFi tomorrow.

K

kg

Guest
One of the many things about this film I didn't get was when a fire broke out in part of the spaceship. They put the fire out by dousing it with just about all of the oxegen they had stored on the ship! I think depressurizing that portion of the ship might have been a safer option for putting out the fire.

A

ayepod

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Ortix":1mvowdwo said:
Hi everyone, hopefully this is the right forum i'm posting in.

To keep things short: I'm doing a physics project as a final exam in my physics class. We have to pick a movie and find the bad physics in it.

I decided to do sunshine and found some interesting things.

However a couple of things are bothering me regarding the shield

First of all, After seperation of the payload (only for those who have seen the movie) looks WAY to small to protect the crew for the return trip.

Second, that small shield looks like a concave mirror (if it's facing the sun) with the ship attached to the back. No, as Cappa is flying towards the payload, you can clearly see some of the light reflecting off the shield.

http://img269.imageshack.us/img269/7184/concave.jpg

Is this possible? I mean, isn't the light supposed to fry him in the first place because an image is formed at the focal point? On top of that, for some reason i think that if light hits the shield, it should not hit it on the edge first but in the center, or am i wrong here?

Could someone clarify this for me? Thanks!

The thing that annoys me about this picture is that the astronaut looks like he is sillouhetted against the sun. Surely if thats the case then the light is hitting him on his left side, he's be dead.

Plus the sun is made smaller than it actually is. The sun is so enormous that by aiming that little shield at any portion of its surface would mean that they would have been fried long ago. That shield is tine compared to the sun and as you approach the surface the curvature of the sun woulda appear to be so small that it would appear you were flying towards a massive wall of fire. The light would have eventually made it over the top of the shield and killed all the occupants IMO

It is only a movie though.

C

chebby

Guest
I rented that movie because of this threat. I loved it. Thanks!

Oh and I have heard that tanks fo algae would be more effective and easier to maintain for prolonged space travel than a bunch of real trees.

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