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Does anyone know of any sites that have information about the physics in outerspace. How things work, forumals to find things ect ect. Basically a good site on physics for outer space such as directions bullets go in events and such. If so could you referre me to ones you find extremely useful. Don''t click me! Killer Eagle Software

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In outer space, there is no air resistance and no (well, technically speaking, just a terribly small amount of) gravity. Therefore, an object will keep going in the direction it is going at the speed it is going until it is stopped by some other force. This means that a player would keep floating off if they didn't apply some other force in another direction (NASA's space-walking jetpacks being an example, having some small engines to boost the astronaut one way or another, controlled via a small joystick).

This isn't a website, but still, it's information.

[edited by - DeathWish on November 20, 2002 1:38:38 PM]

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Is it true in this specific scenerio, say when you have a space ship and your going in one direction and you continue to go in this direction. You rotate the ship around and now your cannons on the ship are facing the direction you are coming from and the back of the ship is moving forward. Now with that in mind the ship fires a bullet the direction the ship is coming from or to the direction of the front of the ship. Will the bullets that are fired go the direction they were shot at or will they continue to move with the ship?

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Yeah, well, if you want realism, you have to go all the way
BTW, is there ANY space related movie that respects those 2 things?

[edited by - Raduprv on November 20, 2002 5:51:05 PM]

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quote:
Original post by DevLiquidKnight
Is it true in this specific scenerio, say when you have a space ship and your going in one direction and you continue to go in this direction. You rotate the ship around and now your cannons on the ship are facing the direction you are coming from and the back of the ship is moving forward. Now with that in mind the ship fires a bullet the direction the ship is coming from or to the direction of the front of the ship. Will the bullets that are fired go the direction they were shot at or will they continue to move with the ship?


If the bullet is fired backward at the exactly the same speed as the ship is moving forward, the bullet will stay motionless. If there is any recoil on the gun, the ship will move forward even faster.

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More interestingly...

If a ship is moving at the speed of light and it fires a laser in the direction of travel then the laser will also be travelling at the speed of light (observed from a fixed observer) and the laser and ship will travel at the same speed and maintain the same position relative to one another.

Gravity is very important in space all though it''s effects are not very easily perceived. Take for instance a sattellite hurtling around Earth. It looks like it''s shooting off in to space but that small effect called gravity keeps it in motion around the planet.

If your working below the speed of light (say <1/3c) then you needn''t worry about relativity and you can just use the newtonian equations for momentum.

Oh and in answer to:
quote:
BTW, is there ANY space related movie that respects those 2 things?


I''m sure I remember some crappy black and white sci-fi things were the ships would move along then the laser would fire and you''d just see a big explosion on the other ship. Certainly not as fun as in Star Wars etc. I''d like to see cannons used in space :-) like a railgun or something! Would be still quite hard to hit anything.

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Physics in space are pretty easy. Firstly, gravity only plays an important role if you''re near a planet. Secondly, the there''s virtually no friction so objects continue moving in the direction they are pushed (by engines, asteroids etc.) until something else pushes them. For guns, when a bullet is launched, it will have the motion the gun gives it, plus the motion of the spacecraft. Like if you''re running and you throw a ball sideways. Also, while relativity is interesting, it probably isn''t worth worrying about unless it affects your gameplay somehow.

tj963

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quote:
Original post by DevLiquidKnight
Would lazers in space be visible if say you were inside of a nebula where it is more dusty thus the lazer would be projected upon the dust particals?

Don''t click me!
Killer Eagle Software


I don''t think the dust is glowing, so there''s at least enough dust to scatter star light, and a laser would be more intense (not more powerful) than a star, especially at a far distance. So I guess it would scatter the laser light pretty good.

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Yeah I guess your going to have pretty high power lasers if they are supposed to do any damage. It all depends on many things though e.g. the focus of the laser beam.

5 minutes before I wrote this e-mail I was playing with class 3B lasers making holographic lenses!! just thought I''d say that hehe

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quote:
Original post by Metorical
If a ship is moving at the speed of light and it fires a laser in the direction of travel then the laser will also be travelling at the speed of light (observed from a fixed observer) and the laser and ship will travel at the same speed and maintain the same position relative to one another.



This is complete nonsense !

First nothing physical, i.e. with mass, can travel at the speed of light. One way of looking at it is that it would take an infinite amount of energy and infinite time to accelerate an object to the speed of light.

Second the speed of light is constant for all observers, including a quickly moving spaceship: even for a ship moving at 99% of the speed of light, when it fires a laser the speed of light measured on the spaceship is the same as the speed measured by people on the ground.

This is the principle of [special] relativity: the speed of light is the same in all inertial frames. For this to be true other things have to be allowed to be different: in particular distance and time are not absolutes, but are different for different observers. The mathematics of it is pretty straightforward once you get your head around the principles.

I''ve not seen it used in games or films: both tend to fake the mechanisms of high-speed travel rather than use relativity. Maybe someone will come up with an interesting way of using it one day.

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quote:
Original post by DevLiquidKnight
Is it true in this specific scenerio, say when you have a space ship and your going in one direction and you continue to go in this direction. You rotate the ship around and now your cannons on the ship are facing the direction you are coming from and the back of the ship is moving forward. Now with that in mind the ship fires a bullet the direction the ship is coming from or to the direction of the front of the ship. Will the bullets that are fired go the direction they were shot at or will they continue to move with the ship?


For bullets fired backwards it depends how fast you are going. If the bullets are much lighter than the ship the ship''s speed will hardly be affected. In this case the speed of the bullets will be

bullet_speed = firing_speed - ship_speed

Where ''firing_speed'' is the speed out of the gun as if it were on the ground.

So if the bullets are fired faster than the ship''s speed they will have a positive speed in the direction they are fired. If they are fired slower they will have a negative speed, i.e. they will be going in the direction of the ship, though at a slower speed.

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A more interesting problem is the physics of objects orbiting around a planet, like a shuttle approaching a satellite. I think there are interesting effects, like if you accelerate naively towards your target, you actually move to a higher orbit.

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1- If a ship fires a bullet while it is accelerating (both go same direction), it eventually catches up with the bullet.

2- If there is a nebula to refract laser light, the friction might be significant.

Air (gas) resistance can be calculated by
Fw = Cw * r * D * v*v
So the force Fw(resistance) is a constant (higher = more air resistance, varies for every shape) r = the air pressure, D is the air density and v*v is your velocity squared.

This could mess up pretty bad if the elapsed time between succeeding simplation steps vary too much. For a game it will do fine unless your velocity is very big.

If you don''t understand forces (Fw) and how they relate to movement I''ll happily explain. For accurate results this won''t do I''m afraid. It will do for a cool little space game.

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The simple formulae will probably mess up, certainly with quickly varying factors (hig accleration for instance).

Your ship could lose control of istelf when it''s going too fast and needs to stop. It will have a hard time accelerating in the opposite direction in order to stop.

It could also be caught in the gravity of some planet/star/big object. That is: it''s engine is too weak to fight the planet''s gravity.

If you implement these physics and play around with them you''ll see.

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quote:
Original post by Raduprv
The higher the speed is, the less manouvrable(sp?) the ship is. So, yes, eventually, the ship will be VERY hard to control.


Not true. No matter how fast it is going the spaceship is as manoeuvrable as it is when at rest.

The thing that makes vehicles difficult to control on Earth is not their speed but their interaction with their environment. E.g. tyres are rated up to a certain speed, car suspensions have to work harder at higher speed, steering needs to change direction quicker at higher speed, etc.

Spaceships have no such interaction. Satellites in low Earth orbits slowly lose speed and fall to Earth over the years, but far away from Earth''s atmosphere even this effect disappears. And it''s easy to design things to use air resistance/drag as a stablising effect (from arrows to Apollo launch rockets). Gravity also has a simple effect that does not destabalise objects.

In space there''s no such thing as absolute velocity, so you cannot meaningfully measure the speed of anything alone. Everything is moving relative to something else, e.g. we move around the Earth every 24 or so hours, the Earth moves around the sun every year, the Sun is orbiting the centre of the galaxy, which itself is moving relative to other galaxies.

It''s possible to measure the relative speed of two objects, to work out how long you need to ''brake'' one of them to match speeds. But unless they are intereacting on some way more complex than drag and gravity this will not make either of them ''hard to control''

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Guest Anonymous Poster
quote:
Original post by johnb
This is complete nonsense !

Only for those who didn''t understand what he meant. Read more carefully!

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Guest Anonymous Poster
quote:
Original post by johnb
Not true. No matter how fast it is going the spaceship is as manoeuvrable as it is when at rest.

If by maneuvering a spaceship one means to make it follow a certain path through space, then yes, it will become harder at higher velocities, since the forces needed for the maneuvering will increase in magnitude. At relativistic speeds maneuvering will become ever harder, as the relativistic mass of the spaceship increases.

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>> This is complete nonsense !
> Only for those who didn''t understand what he meant. Read more
> carefully!

I did read it carefully. I also posted a brief summary of what was wrong with what was written. If you disagree with anything I posted please state where you think I''m wrong. Don''t just post anonymously implying I didn''t understand what he wrote.

> If by maneuvering a spaceship one means to make it follow a
> certain path through space, then yes, it will become harder at
> higher velocities, since the forces needed for the maneuvering
> will increase in magnitude.

You cannot associate a single velocity with an object in space, as there''s no fixed frame of reference. Each uniformly moving object has it''s own frame of reference, and within this frame of reference the dynamics is the same. If you cannot give an object a velocity you cannot associate properties with it, such as manoeuvrability, dependent on it''s speed or velocity.

You can define the velocity of one object relative to another, and you can then work out the energy required to reduce this velocity to zero, i.e. to bring them together so they have the same frame of reference. A higher relative velocty means this will require more energy but but does not make one or both more difficult to control.

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Guest Anonymous Poster
quote:
Original post by johnb
I did read it carefully. I also posted a brief summary of what was wrong with what was written. If you disagree with anything I posted please state where you think I''m wrong. Don''t just post anonymously implying I didn''t understand what he wrote.

Well, I did in fact state were I thought you were wrong. Your summary was fine, but it didn''t contradict Metoricals post. That''s how I figured you had misunderstood him.
quote:
You cannot associate a single velocity with an object in space, as there''s no fixed frame of reference. Each uniformly moving object has it''s own frame of reference, and within this frame of reference the dynamics is the same. If you cannot give an object a velocity you cannot associate properties with it, such as manoeuvrability, dependent on it''s speed or velocity.

If, like I said, maneuvering a spaceship means to make it follow a certain path through space, then you do, by definition, have a reference frame relative to which you move, namely that of the path you''re trying to follow. Following that path at a higher speed is more difficult, as it requires bigger forces and more precise timing.

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