Jump to content

Archived

This topic is now archived and is closed to further replies.

OmniAtlas

Here is a dumb physics question for you smart people

Recommended Posts

Yes that makes sense. So if the trap door is open, and you are inside the ship hovering, you are still relative to earth and going 100 knots?

 

The minute the trap door closes you become relative to the inside of the ship and you should cease all speed?

Not quite cease all speed, you'd still be moving away from earth at 100kts if you think about it right? That speed hasn't gone anywhere, if that makes sense.

 

Basically think of your ship having many different speeds if that helps, so:

100kts relative to earth,

0kts relative to the mothership

70kts relative to jupiter

90kts relative to mars 

 

And so on, these speeds are all happening at once, it just depends on which one you want to use, and which are relevant, in this case the speeds relative to Jupiter and Mars are of no concern to us, just the one relative to earth and to the Mothership.

 

I've probably just made this clear as mud haven't I...  :mellow:

 

Regards,

Ró.


Rónán O Cadhain.

sig_FSLBetaTester.jpg

Share this post


Link to post

 

 


Yes that makes sense. So if the trap door is open, and you are inside the ship hovering, you are still relative to earth and going 100 knots?

The minute the trap door closes you become relative to the inside of the ship and you should cease all speed

 

Not sure if my above post helped at all. You're relative velocity depends on what you're looking at. Your "inertial frame of reference".


Dave Wegner

 

- Don't be afraid of common sense or the search function.

Share this post


Link to post

Are you referring to spaceflight, or atmospheric flight?


Christopher Low

UK2000 Beta Tester

FSBetaTesters2.png

Share this post


Link to post

 

 


Basically think of your ship having many different speeds if that helps, so:
100kts relative to earth,
0kts relative to the mothership
70kts relative to jupiter
90kts relative to mars 
 
And so on, these speeds are all happening at once, it just depends on which one you want to use, and which are relevant, in this case the speeds relative to Jupiter and Mars are of no concern to us, just the one relative to earth and to the Mothership.

 

Exactly.


Are you referring to spaceflight, or atmospheric flight?

 I was thinking spaceflight. Now I'm not sure of the OP's original intentions. I'm at work and have to keep jumping back and forth haha


Dave Wegner

 

- Don't be afraid of common sense or the search function.

Share this post


Link to post

Are you referring to spaceflight, or atmospheric flight?

Space I'd hope, otherwise we'd have all aerodynamic and gravitational forces to take into effect...  :mellow:


Rónán O Cadhain.

sig_FSLBetaTester.jpg

Share this post


Link to post

 

 


When is your speed relative to the inside of the mothership? When the trap door closes or when you enter inside the ship? 

 

It may help to think of yourself and your ship as being satellites. Both entirely with entirely unique orbital properties. Just because you move inside something, doesn't mean that your relative velocity is just going to drop to zero. 

 

If a car drove by at 85 mph (miles. The rest of the world, please feel free to convert to meters haha) with the door open, and timed yourself perfectly and jumped in as it went by, you're not going to have a good day. 


Dave Wegner

 

- Don't be afraid of common sense or the search function.

Share this post


Link to post

Actually, I have "sim" experience with this. Anybody here a fan of the space-sim "Orbiter"?

 

Well, it turns out that if you're, say, 5 meters below the mothership and your relative speed is 0 m/s then that (obviously) going to have (basically) identical orbital parameters. If you thrust "up" into the mothership you've changed your orbital parameters. You're generally going to continue in that direction until you reach your new apoasis (highest point in orbit) and begin the other part of the ellipse and start heading back downhill towards your periapsis. If you're in a perfectly circular orbit to begin with (which really never stays circular due to orbital perturbations/solar wind/etc), then by thrusting in any direction you will change your orbital into an ellipse by some degree. It will not change it very much, but it is without a doubt changing the shape of your orbit.

 

 

That kind of makes sense if I think of it as orbits; as you move into the hanger bay you have to maintain your orbit speed concurrent to the mothership speed, however of course you will have to take into consideration wind resistance, gravity, etc. 

 

I can see how it would be a completely different proposition in space. 

 

Basically think of your ship having many different speeds if that helps, so:

100kts relative to earth,

0kts relative to the mothership

70kts relative to jupiter

90kts relative to mars 

 

And so on, these speeds are all happening at once, it just depends on which one you want to use, and which are relevant, in this case the speeds relative to Jupiter and Mars are of no concern to us, just the one relative to earth and to the Mothership.

 

I've probably just made this clear as mud haven't I...  :mellow:

 

Regards,

Ró.

I just remember the physics experiment we did in high school with the bouncing ball on the moving train :)


Soarbywire - Cockpit building simulation news and resource. Fly the Jeehell Flight Management and Guidance System. A free A320 avionics suite for cockpit builders and aviation enthusiasts. 

Share this post


Link to post

Why not both?

If the earth is moving 250000 mph. absolute in the universe, and the mothership is moving 500 mph. relative to earth in that same direction, it is moving 250500 mph absolute. If it moves 500 mph. relative to earth in the opposite direction, it moves 249500 absolute.

Now lets regard the earth as stationary for the sake of argument. The mothership moves 500 mph. relative to the earth. You are moving 0 mph relative to the mothership. Because if A=B and B=C, A=C, you are therefore moving at 500 mph. relative to the earth AND 0 mph relative to the mothership AT THE SAME TIME. Therefore it does not matter when the trap-door closes or indeed if it ever does. You will still be moving relative both to the earth and to the mothership. Simply closing the door does not make the earth cease to exist.

In practice, when doing a docking scenario like this, the only speeds that matter are the speed of the dock and the speed of the thing that's docking, so if you're landing on a mothership, it does not matter how fast you're going relative to the earth, only how fast you're going relative to the mothership.

Say it takes X% throttle to maintain your speed relative to the earth. It will continue to require that much throttle regardless of your position relative to the mothership. In order to turn off your engines and continue to move at that speed - or rather to continue to move at the speed relative to the earth AND remain motionless relative to the mothership, you want to become physically attached to the ship somehow and move as a single unit. You would want to use some sort of docking grapple, methinks.

Share this post


Link to post

Thanks for the explanation, but what if you don't dock? Do you maintain your current speed (adjusting for resistance) inside the mothership so you are moving consistently relative to earth?


Soarbywire - Cockpit building simulation news and resource. Fly the Jeehell Flight Management and Guidance System. A free A320 avionics suite for cockpit builders and aviation enthusiasts. 

Share this post


Link to post

Thanks for the explanation, but what if you don't dock? Do you maintain your current speed (adjusting for resistance) inside the mothership so you are moving consistently relative to earth?

 

Assuming the mothership is flying at a constant velocity, and you are below it, flying at the same velocity, your speed relative to the mothership is zero. Relative to the earth it is x m/s

 

If you move up into the mothership(without docking), you are still doing x m/s relative to the earth and 0 m/s relative to the mothership.

 

If you dock into the mothership, you are still doing x m/s relative to the earth and 0 m/s relative to the mothership.

 

ie) you will always be travelling at a constant speed relative to the mothership(0 m/s) and earth (x m/s)

 

All of this is of course assuming that there is no acceleration taking place.


voz777_zpsa91dce79.jpg

 

"If you can't solve and equation with calculus, you're not using enough calculus" - A wise friend

Share this post


Link to post

Say it takes X% throttle to maintain your speed relative to the earth. It will continue to require that much throttle regardless of your position relative to the mothership. In order to turn off your engines and continue to move at that speed - or rather to continue to move at the speed relative to the earth AND remain motionless relative to the mothership, you want to become physically attached to the ship somehow and move as a single unit. You would want to use some sort of docking grapple, methinks.

 

 

Assuming the mothership is flying at a constant velocity, and you are below it, flying at the same velocity, your speed relative to the mothership is zero. Relative to the earth it is x m/s

 

If you move up into the mothership(without docking), you are still doing x m/s relative to the earth and 0 m/s relative to the mothership.

 

If you dock into the mothership, you are still doing x m/s relative to the earth and 0 m/s relative to the mothership.

 

ie) you will always be travelling at a constant speed relative to the mothership(0 m/s) and earth (x m/s)

 

All of this is of course assuming that there is no acceleration taking place.

 

Exactly right.

If 1.) It requires some energy input to maintain 0 relative velocity with the mothership and 2.) You don't dock, you would need to keep your engines turned on to maintain position. If aerodynamic lift was part of the equation, you would probably lose that within the ship, leading to an uncontrolled collision.

If either condition is not true, though, then you have no need to keep engines or really another control system turned on once you are inside the mothership - you will continue at the same relative velocities as before, as if nothing had changed.

Share this post


Link to post

No resistance in space. A vacuum. If you're floating around in the docking bay, you will probably slowly float into walls. As others have said, once docked or attached you move as one unit. Also once at a certain velocity and direction, your ship will generally stay that way. You don't need to maintain thrust to "keep up" with the mother ship once you've exactly matched velocity and direction. Atmosphere is different. You're hitting mass particles (air) that deflects around your aircraft and causes lift; gravity has an effect too of course. No resistance or lift in space. Gravity is not an issue, at least at the strengths were used to on earth.


Boeing777_Banner_Pilot.jpg

 

Brent Baker

Share this post


Link to post

No resistance in space. A vacuum. If you're floating around in the docking bay, you will probably slowly float into walls. As others have said, once docked or attached you move as one unit. Also once at a certain velocity and direction, your ship will generally stay that way. You don't need to maintain thrust to "keep up" with the mother ship once you've exactly matched velocity and direction. Atmosphere is different. You're hitting mass particles (air) that deflects around your aircraft and causes lift; gravity has an effect too of course. No resistance or lift in space. Gravity is not an issue, at least at the strengths were used to on earth.

 Truth - the idea of requiring throttle input in space was used to illustrate the way motion works.

Share this post


Link to post

If you're playing pool in Donald Trump's opulent, gold-trimmed Boeing pelf-liner, in straight & level flight (no turbulence), how fast are the balls moving?

 

It's all relative; that's all :lol:

Share this post


Link to post

Thanks for the explanation, but what if you don't dock? Do you maintain your current speed (adjusting for resistance) inside the mothership so you are moving consistently relative to earth?

 

Here, it is important to specify if you are in the atmosphere, in orbit, or in free spaceflight.

 

If you are in a free orbit (no force applied) then your orbital velocity determines your orbital altitude.  If you speed up, you move to a higher-elevation orbit, assuming (for simplicity) a circular path.  This also means that if you come up below the mother ship and match velocities, you can not just "coast" and stay in that position.  You will fall back because you are in a lower orbit.

 

On another point, the trap door is irrelevant to these orbital mechanics, and may be ignored in the calculations.

Share this post


Link to post
×
×
  • Create New...