1g Ships and Size:7 worlds...

[mike wightman]

Wikipedia Link: Whataboutism

<clap> <clap> so you take something out of context for a GOTCHA. Pathetic.
The rest of the post show that this is intended as a rhetorical question.

 

[AnotherDilbert]

A ship on the ground has no vector because it is not moving and has no potential to move in the future because the resultant force on the ship is zero. There is no vector to draw.

There is no resulting vector, no total acceleration.
The forces operating on the craft, like gravity, are always there.
It is not weightless.

The "vectors" that you are plotting are not "vectors" they are forces, the resultant of which is then applied to the current vector in order to determine future position.

Vectors in LBB2 are not force arrows they are displacement arrows, ...

Make your mind up?

Yes,

Yes, force vectors that causes acceleration (F = ma), that integrated over the turn is a velocity vector showing distance travelled per turn. Does that make any difference whatsoever to LBB2 RAW?

Vector movement in Traveller has you drawing displacement vectors, not force vectors.

Displacement per turn, a velocity...

Yes it makes a difference because the final displacement "vector" that is actually drawn on the surface does not represent force, or energy, or velocity. It shows displacement only.

Addition is commutative and associative, the result is trivially the same vector either way.

So aerobraking exists because the rules say so, but lift doesn't?

The rules specify aerobraking, but not lift, yes. Presumably spacecraft doesn't have enough lift to significantly influence the outcome, as their shapes would suggest.

Aerobraking is also a vast simplification, it is e.g. not proportional to speed.

So in level flight lift and weight cancel out yes? And if you apply a 1g continuous thrust to an object with balanced forces what happens?

You are assuming lift is enough, not I.

 

[mike wightman]

There is no resulting vector, no total acceleration.
The forces operating on the craft, like gravity, are always there.
It is not weightless.

The forces balance, there is no resultant force, so no vector is drawn

Make your mind up?

I am saying that you keep plotting "force vectors" where the game requires the plotting of "displacement vectors"

Yes,

Yes

Displacement per turn, a velocity...

It is be we do not track velocity we track displacement

Addition is commutative and associative, the result is trivially the same vector either way.

Yes 100mm-25mm-50mm=25mm

The rules specify aerobraking, but not lift, yes. Presumably spacecraft doesn't have enough lift to significantly influence the outcome, as their shapes would suggest.

Aerobraking is also a vast simplification, it is e.g. not proportional to speed.

I agree, but it would add complication that may not be worth the effort

You are assuming lift is enough, not I.

Yes I am

 

[AnotherDilbert]

Still wrong

Yes, you are still wrong. I used LBB2'77 as specified by the OP earlier. It uses Imperial measurements.

The thrust vector should be plotted to a position 100mm above the planet surface, the midpoint of which places it in the 0.5g band of all planet sizes 8-10.

Gravity does not operate on the ship's acceleration, but the ship's position.
All the accelerations add together to change the velocity vector.

Turn 1: Position [0,0] Velocity vector [0,0]: midpoint of the velocity vector is [0,0] on the planets surface (in the 1.125 G band).
Accelerate upwards by 1 G during the entire turn, add 100 mm upwards.
Gravity accelerates downwards by 1.125 G (the size 9 world used earlier) during the entire turn add 112.5 mm downwards.
Total acceleration downwards 0.125 G (12.5 mm), or in other words "the vehicle cannot move".

 

[AnotherDilbert]

The forces balance, there is no resultant force, so no vector is drawn

Gravity is not optional. It is always on. The acceleration always act on the spacecraft. The acceleration vector is always added.
If you wish to remain still, you have to have an opposite force, an opposite acceleration to balance it out.
The ground can provide that opposite force.

I am saying that you keep plotting "force vectors" where the game requires the plotting of "displacement vectors"
...
It is be we do not track velocity we track displacement

The "displacement" is displacement per turn = distance per time = velocity.

Changes in the velocity vector [distance per time] per turn is acceleration [distance per time per time].


When we use our drive to accelerate we change the velocity vector, that is then used to change our position. Newtonian mechanics.

I agree, but it would add complication that may not be worth the effort

Agreed.

 

[AnotherDilbert]

Does this example from Mayday help?

A: move the ship according to the vector.
B&C: move the vector
D: Apply all changes to the vector without moving the ship.

LBB2 just does it in the opposite order:

In a player’s movement phase, he will indicate the acceleration (new vector) he wishes to apply, and note any gravitational influence vector he is required to apply,and then add them to his ship’s present vector. His ship then moves in the direction of its new vector, for the length of the vector. The vector then remains on the playing surface for reference during the next applicable movement phase.

Change the vector, then when all changes to vector are done, change the position of the ship.



Edit: And that didn't add anything important:

Spoiler

 

[AnotherDilbert]

Let's try accelerating upwards again.

We start on the planet's surface, position [0,0].
We have no velocity, the (velocity) vector is [0,0].

Turn 1: Movement phase:
In a player’s movement phase, he will indicate the acceleration (new vector) he wishes to apply, and note any gravitational influence vector he is required to apply, and then add them to his ship’s present vector.
(1) We accelerate upwards by 1 G: Draw an (acceleration) vector [+100 mm,0] at the end of the (velocity) vector without moving the ship.
(2) The (velocity) vector start at position [0,0] in the direction [0,0], midpoint [0,0] on the planets surface in the 1.125 G band. Add an (acceleration) vector [-112.5 mm, 0] to the end of the other acceleration vector.
(3) If there are no other accelerations, add the accelerations to the velocity vector. The new velocity vector is [0,0] + [+100 mm,0] + [-112.5 mm, 0] = [-12.5 mm, 0].


His ship then moves in the direction of its new vector, for the length of the vector. The vector then remains on the playing surface for reference during the next applicable movement phase.
Move the ship from position [0,0] with the velocity vector [-12.5 mm, 0] to position [-12.5 mm, 0] down into the planet, which we can't, so remain in position [0,0].


Or in other words "the vehicle cannot move".

Eh, I'd better draw that...

 

[mike wightman]

Yes, you are still wrong. I used LBB2'77 as specified by the OP earlier. It uses Imperial measurements.

It shouldn't matter if I move from 77 to 81, but if we work in inches it is the same result.

Gravity does not operate on the ship's acceleration, but the ship's position.
All the accelerations add together to change the velocity vector.

Yes, the half way point of the maneuver vector is affected by the gravity band it is in, which is the 0.5g band.

Turn 1: Position [0,0] Velocity vector [0,0]: midpoint of the velocity vector is [0,0] on the planets surface (in the 1.125 G band).
Accelerate upwards by 1 G during the entire turn, add 100 mm upwards.
Gravity accelerates downwards by 1.125 G (the size 9 world used earlier) during the entire turn add 112.5 mm downwards.
Total acceleration downwards 0.125 G (12.5 mm), or in other words "the vehicle cannot move".

No
the vector is not force, it is not velocity, it is displacement
and you are not applying the rules as written the rules as written say
100-50-25

 

[mike wightman]

Let's try accelerating upwards again.

We start on the planet's surface, position [0,0].
We have no velocity, the (velocity) vector is [0,0].

Turn 1: Movement phase:
In a player’s movement phase, he will indicate the acceleration (new vector) he wishes to apply, and note any gravitational influence vector he is required to apply, and then add them to his ship’s present vector.
(1) We accelerate upwards by 1 G: Draw an (acceleration) vector [+100 mm,0] at the end of the (velocity) vector without moving the ship.
(2) The (velocity) vector start at position [0,0] in the direction [0,0], midpoint [0,0] on the planets surface in the 1.125 G band. Add an (acceleration) vector [-112.5 mm, 0] to the end of the other acceleration vector.

This is not the rules as written

(3) If there are no other accelerations, add the accelerations to the velocity vector. The new velocity vector is [0,0] + [+100 mm,0] + [-112.5 mm, 0] = [-12.5 mm, 0].

Nope. the ship's movement plot is 100mm up.
Half way up that imaginary line, at 50mm, that puts the ship in the 0.5g gravity band.
So we subtract 50mm and then a further 25mm for air resistance
Total 25mm up.

His ship then moves in the direction of its new vector, for the length of the vector. The vector then remains on the playing surface for reference during the next applicable movement phase.
Move the ship from position [0,0] with the velocity vector [-12.5 mm, 0] to position [-12.5 mm, 0] down into the planet, which we can't, so remain in position [0,0].


Or in other words "the vehicle cannot move".

Eh, I'd better draw that...

 

[AnotherDilbert]

and you are not applying the rules as written the rules as written say

Then show me why LBB2 and Mayday are wrong?

 

[AnotherDilbert]

Nope. the ship's movement plot is 100mm up.
Half way up that imaginary line, at 50mm, that puts the ship in the 0.5g gravity band.
So we subtract 50mm and then a further 25mm for air resistance
Total 25mm up.

This is wrong?

LBB2'77, p26: In a player’s movement phase, he will indicate the acceleration (new vector) he wishes to apply, and note any gravitational influence vector he is required to apply, and then add them to his ship’s present vector. His ship then moves in the direction of its new vector, for the length of the vector. The vector then remains on the playing surface for reference during the next applicable movement phase.

 

[AnotherDilbert]

Let me try this again.

LBB2'77, p26:
In a player’s movement phase, he will indicate the acceleration (new vector) he wishes to apply, and note any gravitational influence vector he is required to apply, and then add them to his ship’s present vector. His ship then moves in the direction of its new vector, for the length of the vector. The vector then remains on the playing surface for reference during the next applicable movement phase.

Starting position 0 with Vector 0, none:


In a player’s movement phase, he will indicate the acceleration (new vector) he wishes to apply, and note any gravitational influence vector he is required to apply,

Plot drive acceleration, Vector remains 0, none.

The green arrow is not the ship's new Vector, it will soon be added to the Vector.


Plot drive gravity, Vector remains 0, none.

Neither the green nor the red arrows are part of the ships Vector, they will soon be added.


and then add them to his ship’s present vector.

Plot new Vector, add green and red to old Vector 0:

Everything is added, the purple arrow is the ship's new Vector.


His ship then moves in the direction of its new vector, for the length of the vector.

Move the ship along the Vector, which fails.

 

[AnotherDilbert]

the vector is not force, it is not velocity, it is displacement

?

LBB2'81, p27:
Each ship has a vector, which expresses that ship's velocity as a line (arrow) of a specific direction.

It was a looong time since I actually read that part of LBB2...

 

[atpollard]

Turn 1:

Hypothetically, if I place a FREE TRADER on a GIANT ROLLER SKATE and apply the VECTORS above to it using the GRAV DRIVE … what will happen?

Let’s see if we had the same H.S. Physics instructions for “resolving vectors into vertical and horizontal components”.

[EDIT: I better add a disclaimer that this is just a “what if“ and not RAW.]

 

[mike wightman]

?



It was a looong time since I actually read that part of LBB2...

And it is an error - we are plotting displacement not velocity.

 

[atpollard]

Correct. UP is not the "only direction" available ... but it IS the direction you need to go in order to reach orbit from the surface.

You can answer the question about a FREE TRADER on a GIANT ROLLER SKATE if you want to.
[shrug]

 

[mike wightman]

Let me try this again.


Starting position 0 with Vector 0, none:
View attachment 3586

In a player’s movement phase, he will indicate the acceleration (new vector) he wishes to apply, and note any gravitational influence vector he is required to apply,

Plot drive acceleration, Vector remains 0, none.
View attachment 3589
The green arrow is not the ship's new Vector, it will soon be added to the Vector.


Plot drive gravity, Vector remains 0, none.
View attachment 3588
Neither the green nor the red arrows are part of the ships Vector, they will soon be added.


and then add them to his ship’s present vector.

Plot new Vector, add green and red to old Vector 0:
View attachment 3587
Everything is added, the purple arrow is the ship's new Vector.


His ship then moves in the direction of its new vector, for the length of the vector.

Move the ship along the Vector, which fails.

Your 1g band between the planet surface and the first gravity circle is the error. A size 10 world only has 1.25g on its surface, as soon as you take off you are on the 1.0g band which is only 9mm thick, above that you have the 0.75g line which is an additional 14mm thick, so we are now into the 0.5g band which is an additional 23mm - you know what I should have done this earlier because the midpoint of the 100mm "vector" is in the 0.25g zone.

 

[Spinward Flow]

as soon as you take off

 

[AnotherDilbert]

Hypothetically, if I place a FREE TRADER on a GIANT ROLLER SKATE and apply the VECTORS above to it using the GRAV DRIVE … what will happen?

Let’s see if we had the same H.S. Physics instructions for “resolving vectors into vertical and horizontal components”.

[EDIT: I better add a disclaimer that this is just a “what if“ and not RAW.]

LBB2 does not describe this, but in physics the ships would roll along the surface of the planet, keeping the velocity vector tangential to the planet surface, as I discussed a few days ago:

Let's assume the planet is a perfectly smooth billiard-ball and you can roll on it without friction (leaving RAW and physics far behind):

The length of a line tangential to the planet surface to the 1 G line is about 7½", so you would need a velocity vector of 15" parallel to the surface for the midpoint of the vector to fall outside the 1 G band, freeing you from the shackles of the gravity well (according to LBB2).

You can accelerate at 2" every turn, braked ¼" (⅛ G) by the atmosphere, so resulting 1¾" added velocity per turn. Gravity isn't a factor, as we are supported by the ground (without any friction).

You would need 15" / 1¾" ≈ 9 turns ≈ 1.5 h to achieve that speed.

1.5 h at ⅞ G is... Sorry, I can't be bothered with Imperial units, and as I am not a subject of His Britannic Majesty I have freedom not to.
1.5 h at 0.875 G is a velocity of 1.5 h × 3600 s × 8.75 m/s ≈ 47 250 m/s ≈ 170 000 km/h (~106 000 mph for subjects), travelling a distance of d = at²/2 = 8.75 m/s × 5400² / 2 ≈ 127 500 km.

With a 7000 km world radius, that is a circumference of about 44 000 km.

So, we would need a runway all around the world, and go around it almost three times.


I would call that a slightly problematical approach...

The roller skates would not, as anyone ever using them would confirm, slide off into space...
Actual roller skates would have enough friction to keep velocity well below orbital escape velocity.

 

[mike wightman]

If its any consolation I don't think this can be correct - a 1g ship can not lift off like a rocket from a 1.25g world, but the rules say otherwise.
But that is the problem with gross simplification.

To get a vector 100mm in length a 1g engine has to "burn" for 1000s.

For gravity to add 100mm you would have to be in that gravity band for 1000s, but since it is only a few mm thick you are through it in only a fraction of that.

Which is why I houseruled streamlined ships can fly.