Three dumb design questions

[Straybow]

Yeah, we know mass is not force, but we're lazy and often conflate the two to simplify discussion.

A=n/g is perfectly reasonable for CT and other variants that use handwavium reactionless thrusters. Whichever variant uses Heplar, you are screwed if you land on a planet with higher gravity than your drive.

 

[DaveShayne]

Originally posted by Rover:
For any given mass M, on a 4G world it will have a weight of 4M. In order to accelerate that mass vertically we gave to apply a thrust force greater than 4M, that is all. It is not a matter of acceleration. It is the excess force above 4M that will cause acceleration.

It is solely a mater of acceleration. That you can't understand that is, I suspect, a product of a substandard education. I'm sorry if I'm being an ass here but you are demonstrably wrong and should shut up now.

 

[aramis]

Dave is quite right. Rudely blunt, but correct.

You don't need to know Mass when you know acceleration and Local G's, since both share a factor of M, and it can be factored out in figuring Delta-V (ΔV).

Basic Algebra.

SInce Tv (Thrust, Vertical) must exceed Gl (G's local) to have positive ΔV, you have several ways to get that thrust: aerodynamic lift, direct vertical thrust, medium-displacement buoyancy, or gravity interruption. All four are available in Traveller (and are all used in TNE and T4), and three are used IRL. TNE couples gravity interruption (98%) with the resultant buoyancy as a means of getting high enough to kick in the HEPlaR.

(Buoyancy is a difference in weight, and is specifically mentioned in FF&S...)

 

[DaveShayne]

Originally posted by Aramis:
Rudely blunt

Sorry. I got frustrated.

 

[TheEngineer]

Stay cool

Guess its its recommended just to observe acceleration, neglet its motivation and treat it correctly as a vector. The rest really is - as Aramis stated - basic (vector) algebra.

The a=n/g thing is perhaps a wrong direction. Just check what happens if g value starts to get small (e.g. g=0,1 N=1 results in a=10 ?????).

Regards,

Mert

 

[Rover]

Originally posted by DaveShayne:
</font><blockquote>quote:</font><hr />Originally posted by Rover:
For any given mass M, on a 4G world it will have a weight of 4M. In order to accelerate that mass vertically we gave to apply a thrust force greater than 4M, that is all. It is not a matter of acceleration. It is the excess force above 4M that will cause acceleration.

It is solely a mater of acceleration. That you can't understand that is, I suspect, a product of a substandard education. I'm sorry if I'm being an ass here but you are demonstrably wrong and should shut up now. </font>[/QUOTE]You are correct you are being an ass. I guess I was under the mistaken impression that we were having a polite discussion.

 

[mike wightman]

[moderator]
Can we please cool things down here guys.
[/moderator]

 

[Rover]

I apologize if I have upset anyone. Maybe there was some point of his I was not getting, maybe I was not clear in my points, but in any case I do not feel it was approprite to call my education into question and then tell me to shut up. I did not see that reaction coming and I was felt a little blind sided when I logged on this morning.

I have been coming to this board on and off for 3 1/2 years and this is first time I have been treated this way. So yes I took exception to it.

I guess I am done with this thread now

Thanks for your time.

 

[TheEngineer]

Really no apologies necessary, Rover.
Most people here are friendly, behave well and are perhaps able to argue in a peaceful way

 

[aramis]

Fundamentally mass is irrelevant given that Traveller drives impart a vector of a known value; we neither need to know nor account for mass in anything other than collisions, since gravity will affect the sum total of the mass equally, as do the traveller drives.

Rover: when you assert the absurd, it inherently brings up questions about your education. Most of us don't post those quandries. To hear me typing half the time would be to listed to a string of invective.

I have been on the other side; for example questioning/attacking the validity of low sample size statistics used as the basis for extrapolation by Astronomers...

 

[Malenfant]

I have been on the other side; for example questioning/attacking the validity of low sample size statistics used as the basis for extrapolation by Astronomers...

Yes, but you failed to understand (and apparently still fail to understand) that the sample sizes are irrelevant there. The physics remains valid regardless of how big or small the sample it's based on is. You can have a sample of one for all I care, but if you can figure out the physics behind how it works then that applies to everything. Sure, you'll miss a lot of the details without more samples, but scientists are good at gleaning every scrap of valid information from the smallest of datasets - and usually understanding the general process is what matters, not the details. And they're also good at recognising which bits of data aren't relevant or useful either.

Either way your opinions on the validity of the science weren't remotely relevant to the discussion. If you want to complain about the validity of the science, then go complain to the people who do the research - because it really isn't relevant here. But that thread wasn't presented as something that people who knew little about the subject could hijack and use as a soapbox to present their own flawed perceptions of science or reality - it was presented as some interesting new research that some people might like to know about to use in their realistic scifi universes if they wanted to. Unfortunately the interesting discussion about the implications of that research got sidelined - and, more ridiculously, the thread was actually locked - because you and Tom insisted on continuing your irrelevant (and factually incorrect) thread-crapping.

The trick about education is that people who don't know a lot about a subject should shut up and listen to those who do know a lot about it. Ask questions by all means, but don't think you know more than the teacher. The unfortunate thing about the internet is that a lot of people who know little or nothing about a subject pretend that they know better than the experts and pass off their opinions as facts when they're not.

EDIT: As for this thread, I think Dave's reaction to Rover's posts was pretty much uncalled for. Even if Rover is incorrect, there's no need to round on him like that. If he insists that he is correct when people who do know more about it correct him on the matter then there's some cause to berate him, but there's a difference between someone just being rusty on a subject (which I think Rover is) and someone deliberately claiming that they know better when they actually don't.

 

[Straybow]

Originally posted by TheEngineer:
Stay cool

Guess its its recommended just to observe acceleration, neglet its motivation and treat it correctly as a vector. The rest really is - as Aramis stated - basic (vector) algebra.

The a=n/g thing is perhaps a wrong direction. Just check what happens if g value starts to get small (e.g. g=0,1 N=1 results in a=10 ?????).

Regards,

Mert

'Scuse me, I just copied the A=n/g without thinking of nit-picky objections. Naturally it would have a limiting condition of A=n for g < 1.0 but I thought that was obvious because we're talking about lift-off from a planet with g > n.

 

[jhulse]

WOW.
I go away on a LARP weekend and look what happens!
In all reality, as long as a Science Fiction GAME setting stays close to Current understandings of physics and reality, that's ok with me. M-Drives are reactionless thruster plates (I think - depending on which system you use) and I'm assuming there aren’t any current physics that explain that.
Here is my ruling on the matter for my campaign.
I will combine the idea from TNE (that I have never read) and GURPS Traveller (that I have) and say that M-Drives not only provide thrust based on their rating, but also negate up to 3 G's of force, so a liner can accelerate up to 3 G's without passengers taking any notice.
I’m not physics major, but I have interest in all sciences. I can generally understand concepts, but don’t ask me to do complex equations in my head!
Once and ship breaks orbit, the tables to travel to a safe distance comes into effect. Other than that, if a ship dose not have a large enough M-drive, the time it takes to reach orbit doubles with each G-rating above its M-rating (plus the contra-grav systems). So all ships can reach orbit on a 3g world or higher (because of contra-grav) but anything over that, their M-drives have to compensate. It may be simple and dumb and most likely doesn’t fit into a physics equation, but neither does a jump field.
So, there it is. Does this seem like a reasonable rule of thumb for a game?
My idea of a deep atmosphere setting in a high G environment wasn’t supposed to spark a heated debate. BUT, I really appreciate all the input. You guys who are the tech-heads ALWAYS impress the heck out of me. But I think sometimes the scientist and physicist you many of us get in the way of keeping this a fun “reality” based Sci-fi game. Just my opinion.

By the way Piper, the link to the meson factory was really cool. That got me thinking…. (uh-oh)
Has anyone considered breaking down a spinal weapon into individual components?
Say, 50% of the tonnage could be taken up by the main weapon with a 20:1 ratio or less, and the remaining 50% can be broken down into several rooms: “injectors”, “accelerators”, “storage”, “energizers”, and a myriad of other components. This could give characters even more possibilities of sabotaging a ships primary weapon.
Any thoughts?

Thanks for all the advice.

Jak Naz

 

[Rover]

Arimis said,” Rover: when you assert the absurd, it inherently brings up questions about your education."

Please tell me Arimis, what exactly in my posts is absurd? Are you refereeing to my formula a=n/g, which I clearly state is not for the real world, just for Traveller. Is that any less absurd than a world where mass does not effect acceleration?

And

Malenfant said, "Even if Rover is incorrect, there's no need to round on him like that. If he insists that he is correct when people who do know more about it correct him on the matter then there's some cause to berate him, but there's a difference between someone just being rusty on a subject (which I think Rover is) and someone deliberately claiming that they know better when they actually don't.


Well take a few days off and I still see I am a topic of discussion.

I do not feel I was wrong about anything I posted, although I do admit I am rusty, as I said earlier it has been 23 years since I took HS Physics.

As for my exchange with DaveShane, maybe we were just misunderstanding each other but I think we were basically saying the same thing. As I said earlier I thought we were talking past each other.

I thought he was using terms for force and acceleration interchangeably, when to the best of my knowledge from a 23 year absence from physics, they are not. All this time, all I have been saying, is that in order to accelerate an object we have to apply force to it. (Which is still true, even for an old fart like me.) From reading the other posts, I guess I was the only one having that difficulty so the problem is clearly on my end. So maybe in today’s world you can use the term 4Gs of acceleration to indicate a force.

For example, a passage I had a problem with was, “Yes and applying that force will require just over 4Gs of acceleration to counteract the 4G constant acceleration of the local gravity.”

“4Gs of acceleration” to me means a change in velocity of approximately 40 meters per second squared. In order to move, or accelerate an object upwards you do not need to change it’s velocity by such a degree. You need to apply an upward force (Lift, Thrust, Contragravity, buoyancy or what have) you counteract the downward force caused by gravity. All I was trying to say was you do not need to change it’s velocity by 40 meters per second squared in order to lift anything off a 4G world.

So again I would like to aplogize for any consternation I have caused and I hope I have clarified what I have been trying to say.

 

[DaveShayne]

Originally posted by Rover:
All I was trying to say was you do not need to change it’s velocity by 40 meters per second squared in order to lift anything off a 4G world.

Accelleration and velocity are not the same thing. Velocity is what is left after all accelerations are applied to a body.

That planet is pulling down at the constant acceleration of 40 m/s^2 (4Gs.) In order to lift from that planet you need to apply a constant acceleration (from thrust, lift or some other means) greater than the acceleration of the planets gravity. If you don't apply that 4G acceleration you are stuck on the ground. If you stop applying the 4G acceleration before acheiving escape velocity you will fall back to the surface.

In your propsed alternative gravity is changed from being a force in it's own right capable of applying an acceleration to a divisor (in the language of math a scalar as opposed to a vector) of another bodies force. Apples in your universe don't fall from trees. They stay just where they are untill something pushes them. If whatever pushes them pushes them up they will eventually reach orbit. This is demonstrably not the case in either the real world or the Traveller aproximation thereof.

 

[Plankowner]

The differece here seems to be when talking about GRAVITY.

The equation is F = M*a
F is the FORCE on the object, M is the MASS of the object, a is the ACCELERATION of the object

Where things get funky is with Gravity. There is a Force of Gravity and an Acceleration due to gravity. Most people use the terms interchangeably because the MASS is constant.

When we start talking about contra-gravity etc, everyone needs to be VERY careful in what term they really mean. 4G's is an acceleration of about 40m/s^2 or it can mean the FORCE required to accelerate a given mass at 40m/s^2. I think if everyone thinks about what they are trying to say, then it might clear up some of the confusion.

Now here is what I THINK people are trying to say.

A contra-gravity field is able to negate the FORCE of gravity within a certain area. As a result, without the force of gravity holding an object on the surface of the planet, an object can change it's velocity very easily (vertically at least). Such that an air/raft can reach orbit in SIZE hours.

If you want to launch a space ship off of the surface of a planet without using contra-gravity, then you will need to supply a force that is greater than that of the local gravity.

If we assume that the mass of the object is unchanged then the force that the ship must produce must be able to accelerate the ship vertically greater than the acceleration than would be caused by that ship being in freefall at the same location (acceleration due to gravity).

When people speak of a 3g world, they are talking about the force of gravity equivalent to the force necessary to accelerate an object of given mass at 3*9.81m/s^2.

I'm not trying to pick on anyone here, just clarify the physical terms.

One final note, assuming that the mass of a ship would be constant when it blasts off to orbit is not a valid assumption without contra-grav. Current rockets spend almost all of their mass as propellant to get a relatively small mass into orbit. They are using the FORCE of the propellant to overcome the FORCE of gravity.

 

[DaveShayne]

Originally posted by Plankowner:
One final note, assuming that the mass of a ship would be constant when it blasts off to orbit is not a valid assumption without contra-grav.

Traveller manuever drives (in all versions except CT's heplar) act like reactionles thrusters. They still have to overcome local gravity but they don't require reaction mass to function. As such they won't use any large amount of fuel going to orbit.

All other points in your post are correct as far as I can tell.

 

[aramis]

Rover: I believe Dave just covered it, nicely.

Further, You don't need to know the forces themselves to do vector maths, only the resultant accelerations imparted, times accellerated, and resultant speeds. The forces and masses involved are, in fact, meaningless in the end, merely a means of getting the vectors in question.

So, if a world's gravity is 4G, it imparts either 4x9.8m/s/s downward acceleration or 4x10m/s/s in the OTU. If we have a ship with a given rating of 3G, it likewise is going to have a vector of 3x9.8 or 3x10 (RW or OTU) m/s/s. let us assume direction 0 is up, and 180 is down. Apply the vectors: 40m/s/s@180deg and 30m/s/s@0deg, your net vector is 10m/s/s@180deg. Which, in the absence of a structure underneath, such as the ground, will result in declining altitude. Given the structure, it results instead a 10m/s/s*mass force into the structure supporting the ship. Since we seldom think about the structure of the ground as having a mass limit, we seldom worry about this.

Nothing in traveller says that drive accelerations are post gravity. Several places point out that they are applied at the same time, specifically, Book 2!

Mal: Neither the time not the place to hash it out.

 

[DaveShayne]

Originally posted by Jak Nazrith:
I can generally understand concepts, but don’t ask me to do complex equations in my head!

You don't really need to do any complex math. If your ship's acceleration is > local gravity it can achieve orbit. If not it's stuck on the ground. Throwing in 3Gs of gravity nullification and a 1G ship will be just stuck on a 4G world. But real planets rarely have even numbered gravities so call that a 3.99G world and get to orbit. (3.99 - 3Gs nullified is less than 1G accelleration.) Don't sweat the time factor too much - if the ship in question has a much higher acceleration than the planetary gravity it will be in orbit in a few minutes. If the manuever drive is just barely good enough use the air/raft time to orbit kludge for the time involved. If local gravity exceeds the drive rating plus any contragrav aparatus then the ship doesn't get spaceborne without some other help. (Perhaps booster rockets or a linear accelerator.)

 

[TheEngineer]

Hi !

Its one of Travellers' mysteries, that in 25 years the 1 g m-drive lift-off topic wasn't described in some more specific way

(Ok, I do not count SOM).
Perhaps it was left out to motivate discussions...

Amyway I have to admit now, that without more specific information even the A=n/g thing could work. At least its as good as SOM overdrive or MTs local g cancelation(?).
Or does Mr. Knowledgebase Aramis has some more specific cannonical sources regarding "m-drives and local gravity" ?

Regards,

Mert