I think that plankowner hits the nail on the head when he says, There is a Force of Gravity and an Acceleration due to gravity. Most people use the terms interchangeably because the MASS is constant.
This I think has been the root of our disagreement. While I was thinking (perhaps incorrectly) of acceleration solely in terms of a resultant (sum, total, overall, net, whatever term is mathematically correct) change in velocity, you were using it to denote a force.
DaveShane said Accelleration and velocity are not the same thing.
I have never tried to claim that acceleration was velocity, I am not sure how you jumped to that conclusion. What I was trying to explain was that when you were saying 4G acceleration, I was misunderstanding what you what you were saying as an overall (net, total…) acceleration and not a force, but thanks to plankowner, I think we are now on the same page, regarding this topic in terms of the real world.
DaveShane said 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.
I attempted to say this very thing, however where you use the term acceleration I was using the term force. Even if I was using incorrect terms I think you could get what I was trying to say, this is not a physics class afterall. What I said was, ” 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.”
Again I agree in the real world, but as I will illustrate later, the real world has very little to do with space travel in Traveller.
DaveShane said: 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.
This where you loose me and I apologize if my limited knowledge of physics is frustrating you. I am not trying to say that gravity should not be a force, and I am not trying to rewrite Newton and I would still want apple to fall (unless they were in zero G
. My proposed equation was merely an attempt to apply what another poster had called handwaivium to the question. As stated earlier the Traveller universe is a bizzaro universe where mass does not matter, thrust does not exist and the limiting factor to a ship’s acceleration is its volume. This acceleration is expressed as a whole multiple of 1 earth gravity.
As Arimis and other people have said, if mass remains constant you can factor it out. True enough in the real world, but in Traveller a ship’s acceleration remains constant regardless of mass. Let’s look at this example, assume a ship floating free of any gravity well for the following:
200 ton Free trader volume has a volume of 2800 cubic meters. 1 Ton = 14 cubic meters.
If a full 10% of that ship is the hull, bulkheads, super structure and other solid components, and all of that has the same density as iron, that ship would have a mass of 2,204,720 KG (Density of iron is 7874KG per cubic meter X 280 Cubic meters.)
If that ship is running with its hold empty, using F=MA the force needed to accelerate that mass at 1 gravity is F = 2,204,720 X 9.81 F= 21,628,303.2 Newtons
Yet if that same ship’s cargo hold is filled entirely with uranium it will still accelerate at 1 gravity using the same engines and the same power despite having an additional mass of 21,869,400 KG (82 tons X 14 cubic meters per tone X 19050 KG per cubic Meter of uranium.)
Plugging these numbers into F=MA, this same ship’s engines are now capable of producing a thrust of 239,167,117.2 Newtons.
Feel free to plug in any other reasonable assumption for the mass of a ship you want and I am still highly confidant in saying that nobody would concede the above is even remotely possible in the real world.
In the Traveller Universe that is the way things are, so please tell me, given all the above disregard for RW Physics, why on a high G world would the equation A=N/G be so unreasonable a convention to ease game play. I would even be open to a limiting factor of A=N for gravities of less that 1G.
For added fun, if we could take those 239 million Newtons and apply them to an empty ship
F=MA, 239 000 000 = 2 200 000 X A A would equal 108.6363… Meters per second squared or approximately 11 Gs. On a 4g world you would still have a net acceleration of 7Gs
So for the sake of RW accuracy IYTU you are free to apply any real world equation and value for any force, acceleration or gravity you wish. IMTU I’ll stick with the game rules and let reality flavor the game play not take it over.
Respectfully,
R
PS Just for comparison, according to Boeing, a 747-8 has a Maximum Takeoff Weight of 960,000 pounds (435,456 kg) and thrust of 66,500 pounds.
http://www.boeing.com/commercial/747family/747-8_facts.html
This I think has been the root of our disagreement. While I was thinking (perhaps incorrectly) of acceleration solely in terms of a resultant (sum, total, overall, net, whatever term is mathematically correct) change in velocity, you were using it to denote a force.
DaveShane said Accelleration and velocity are not the same thing.
I have never tried to claim that acceleration was velocity, I am not sure how you jumped to that conclusion. What I was trying to explain was that when you were saying 4G acceleration, I was misunderstanding what you what you were saying as an overall (net, total…) acceleration and not a force, but thanks to plankowner, I think we are now on the same page, regarding this topic in terms of the real world.
DaveShane said 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.
I attempted to say this very thing, however where you use the term acceleration I was using the term force. Even if I was using incorrect terms I think you could get what I was trying to say, this is not a physics class afterall. What I said was, ” 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.”
Again I agree in the real world, but as I will illustrate later, the real world has very little to do with space travel in Traveller.
DaveShane said: 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.
This where you loose me and I apologize if my limited knowledge of physics is frustrating you. I am not trying to say that gravity should not be a force, and I am not trying to rewrite Newton and I would still want apple to fall (unless they were in zero G
. My proposed equation was merely an attempt to apply what another poster had called handwaivium to the question. As stated earlier the Traveller universe is a bizzaro universe where mass does not matter, thrust does not exist and the limiting factor to a ship’s acceleration is its volume. This acceleration is expressed as a whole multiple of 1 earth gravity.As Arimis and other people have said, if mass remains constant you can factor it out. True enough in the real world, but in Traveller a ship’s acceleration remains constant regardless of mass. Let’s look at this example, assume a ship floating free of any gravity well for the following:
200 ton Free trader volume has a volume of 2800 cubic meters. 1 Ton = 14 cubic meters.
If a full 10% of that ship is the hull, bulkheads, super structure and other solid components, and all of that has the same density as iron, that ship would have a mass of 2,204,720 KG (Density of iron is 7874KG per cubic meter X 280 Cubic meters.)
If that ship is running with its hold empty, using F=MA the force needed to accelerate that mass at 1 gravity is F = 2,204,720 X 9.81 F= 21,628,303.2 Newtons
Yet if that same ship’s cargo hold is filled entirely with uranium it will still accelerate at 1 gravity using the same engines and the same power despite having an additional mass of 21,869,400 KG (82 tons X 14 cubic meters per tone X 19050 KG per cubic Meter of uranium.)
Plugging these numbers into F=MA, this same ship’s engines are now capable of producing a thrust of 239,167,117.2 Newtons.
Feel free to plug in any other reasonable assumption for the mass of a ship you want and I am still highly confidant in saying that nobody would concede the above is even remotely possible in the real world.
In the Traveller Universe that is the way things are, so please tell me, given all the above disregard for RW Physics, why on a high G world would the equation A=N/G be so unreasonable a convention to ease game play. I would even be open to a limiting factor of A=N for gravities of less that 1G.
For added fun, if we could take those 239 million Newtons and apply them to an empty ship
F=MA, 239 000 000 = 2 200 000 X A A would equal 108.6363… Meters per second squared or approximately 11 Gs. On a 4g world you would still have a net acceleration of 7Gs
So for the sake of RW accuracy IYTU you are free to apply any real world equation and value for any force, acceleration or gravity you wish. IMTU I’ll stick with the game rules and let reality flavor the game play not take it over.
Respectfully,
R
PS Just for comparison, according to Boeing, a 747-8 has a Maximum Takeoff Weight of 960,000 pounds (435,456 kg) and thrust of 66,500 pounds.
http://www.boeing.com/commercial/747family/747-8_facts.html
