NationStates Jolt Archive

I realize that this discussion may apply to FT threads more than others but everyone is welcome to participate.

It is obvious to me that there are some folks on this forum that truly have a solid grasp of physics and those principles associated with that field. It is also obvious to me that I am NOT one of those individuals. I am fascinated by physics but I have no real knowledge. That being the case, I thought I might start a thread wherein people like me could ask physics related questions and perhaps receive answers from those that know. Discussion is always welcome as some might see things differently (See thread on whether fighters are obsolete in NS FT :) ) but I'm hoping that the goal here might be to educate those that are interested rather than argue with those that oppose.

Anyway, I wanted to start off by asking a couple of questions:

1) Help me understand the concept of vacuum in space. Is it simply the absence of gravity or is it more complicated than that?

2) Speaking of gravity; is it gravity that keeps us from accelerating uncontrollably when we drive our cars on the surface of the Earth? In other words, why does our velocity no continue to climb as we accelerate like it would in space? Even if I maintain a constant accel in space, my velocity would continue to climb, wouldn't it? Eventually, I would attain a significant percentage of lightspeed, right?

A vacuum isn't an absence of gravity, it's an absence of anything - a pure vacuum, like space, has no particles in it whatsoever, hence why sound can't travel through it for example.

1) There's nothing there. Sound cannot travel because there is no medium for it to travel in.

2) There's nothing applying a backwards force. For example, on earth a car decelerates because there's friction. A constant velocity is when the forces acting on an object all cancel each other out. When in space, there is nothing to cancel the forwards speed out (unless you crash into something, I guess), so you constantly keep going. However, mathematically you can never reach the speed of light.

2) There's nothing applying a backwards force. For example, on earth a car decelerates because there's friction. A constant velocity is when the forces acting on an object all cancel each other out. When in space, there is nothing to cancel the forwards speed out (unless you crash into something, I guess), so you constantly keep going. However, mathematically you can never reach the speed of light.

So is it the Earth's atmosphere that provides the friction? The "backwards force" as you put it? Also, why can't you reach the speed of light mathematically speaking? Please bear in mind that I am not asking in order to argue. I am asking because I do not know.

I do not remember the formula exactly, but there's a part that dictates 1- (c / c2), where 'c2' is the speed of the object, whereas 'c' is the speed of light. If it equal, then it becomes 1-1 = 0, which is not feasible. Hence an error. I'll try to find the formula.

And yes, atmosphere and air particles (yay).

1) Help me understand the concept of vacuum in space. Is it simply the absence of gravity or is it more complicated than that?

vacuum is the absence of matter. However vacuum does itself have an underlying "substance" of a kind: see here. (http://en.wikipedia.org/wiki/Vacuum_energy)

2) Speaking of gravity; is it gravity that keeps us from accelerating uncontrollably when we drive our cars on the surface of the Earth? In other words, why does our velocity no continue to climb as we accelerate like it would in space?

It's not gravity, it's friction that slows us down. The friction comes both from the atmosphere and from the driving surface.

Even if I maintain a constant accel in space, my velocity would continue to climb, wouldn't it? Eventually, I would attain a significant percentage of lightspeed, right?

Yes, except you'd have run out of fuel long before that. The closer you get to lightspeed the more energy you need to accelerate further. At very high percentages of c the total energy cost required to accelerate is more than all the energy in the universe.

I guess this is a pretty basic question.

Let's say an object in space is travelling nearly at the speed of light. Some kind of force (for example gravity) makes it accelerate. Why can't it reach the speed of light?

Better leave out this Vacuum Energy - it would be too much when we have to explain simple friction ;)


The force of friction goes like this: F=N*f , where N is the force which an object exerts on surface (on flat surface it is equal to weight - mass*gravitational acceleration - and on the slope it is multiplied by cosine of the angle of slope to flat surface) and f is the friction coefficient (dependant on the substances of which the object and the surface are made). The letters ( ;) ) can vary, though.

Also, why can't you reach the speed of light mathematically speaking?Relativistic kinetic energy is KE(R) = gamma - 1 x m x c^2, where gamma is the lorentz factor, m is mass and c is the speed of light.

The lorentz factor is gamma = 1 / (1 - v^2 x c^2)^0.5, with v being the speed of the object in question.

Now, the simple problem - if v = 1 & c = 1 then gamma = infinity. Which essentially means that to accelerate a mass - regardless of its restmass, unless it's zero - to c, you need an infinite amount of energy. As the universe's energy is finite, it's not possible.

1) Help me understand the concept of vacuum in space. Is it simply the absence of gravity or is it more complicated than that?
Technically, there is a VERY VERY VERY VERY AMAZINGLY sparse gas in space, and there is, surprisingly enough, a speed of sound apparently. Doesn't do jack, but it apparently exists.
Linky: http://en.wikipedia.org/wiki/Bow_shock mentions some stuff about supersonic and subsonic solar wind o__O

The amount of gas really amounts to nothing. It's so sparse that you don't need to consider it in physics problems, but it exists.

2) Speaking of gravity; is it gravity that keeps us from accelerating uncontrollably when we drive our cars on the surface of the Earth? In other words, why does our velocity no continue to climb as we accelerate like it would in space? Even if I maintain a constant accel in space, my velocity would continue to climb, wouldn't it? Eventually, I would attain a significant percentage of lightspeed, right?
There are a few reasons.

First is that there's so much friction on earth that you eventually reach a terminal velocity, at which the force of your engine is perfectly balanced by the force of friction (air resistance, wheel friction) Second is that your engine can only spin so fast. It eventually reaches a point where it will rip itself apart.

As for in space, I believe that C is like an asymptote on a graph. You can get infinitely close, close enough that in all reality we can approximate you as going C and never know the difference, but perfect C is impossible.

1) Help me understand the concept of vacuum in space. Is it simply the absence of gravity or is it more complicated than that?

A vacuum is dangerous for noble gases and other of the kind in space. This causes greater expansion and it directly proportional to their natural movement as they attempt to equal equilibrium. However gravity of more massive obects can change this.

In an ideal vacuum no particles exist.
In an ideal space nothing exists.

Gravity is the controlling force that makes objects fall around each other as one. If you have massive enough objects they can have their own orbit and can hold particles together. (See all asteral bodies)

2) Speaking of gravity; is it gravity that keeps us from accelerating uncontrollably when we drive our cars on the surface of the Earth? In other words, why does our velocity no continue to climb as we accelerate like it would in space? Even if I maintain a constant accel in space, my velocity would continue to climb, wouldn't it? Eventually, I would attain a significant percentage of lightspeed, right?

This comes from the terms acceleration and velocity.

Acceleration is how fast you are moving to a relative point.
Velocity is how fast you are moving across an infinite point.

Acceleration can be 0, but velocity can be 100 mph. You are not changing speed and are moving at constant rate. In space you must deal with velocity more then acceleration. Everything should be described in vectors for movement and control. Acceleration is/should be used only to describe how fast you can gain speed in the vacuum of space.


No Endorse - Your usage of terminal velocity is wrong. Terminal velocity is where your velocity cannot increase because of friction of the air under your own natural acceleration from free-fall. When you hit this limit you will travel no faster unless you have another way to generate additional acceleration. The only time when breaking apart should be used is far in excess of terminal velocity and under normal standards should never be counted for in itself for technical failures.

1) As they said, space is a vaccuum because there's (virtually) nothing out there. People may profess dark matter and space dust and gas, but if it's there, it's so minisculely thin, it doesn't make a difference.

2) On Earth, we CAN keep accelerating, only the mechanics of the object keep it from accelerating. For instance, we can't keep accelerating forever as we run, that's ridiculous, our muscles can't move that fast. Friction is really what slows us down, it provides a "backwards force" which causes deceleration. And yes, as you go through space at a constant acceleration and your velocity would keep increasing. However, as you get closer to the speed of light (here's where things get quirky) that energy that seems to be making you go faster is now making you more massive as well (one of the fundamental laws of physics is mass remains uncahnged, so this gets confusing). And yes, if you kept going you would eventually reach a good fraction of light speed, but this is theoretical because you would either need an extremely powerful accelerator (and a very strong body to withstand all the force of acceleration), or a very long life if you ever get going that fast. However, you cannot reach the speed of light because, theoretically, you yourself would turn into light from the sheer energy needed to attain that speed.

Basically,
1) It means there's nothing there
2) rough surfaces make things slow down, and yes, to an extent.

No Endorse - Your usage of terminal velocity is wrong. Terminal velocity is where your velocity cannot increase because of friction of the air under your own natural acceleration from free-fall. When you hit this limit you will travel no faster unless you have another way to generate additional acceleration. The only time when breaking apart should be used is far in excess of terminal velocity and under normal standards should never be counted for in itself for technical failures.

1: PLEASE PLEASE PLEASE use the Quote function. It's not hard, yet it saves so much effort deciphering otherwise unintelligible posts.

2: Note that I said "reach a terminal velocity," not "reach Terminal Velocity." -_- the difference is rather important, since "a terminal velocity" means "a final velocity."

The only time when breaking apart should be used is far in excess of terminal velocity and under normal standards should never be counted for in itself for technical failures.
Second is that your engine can only spin so fast. It eventually reaches a point where it will rip itself apart.
Emphasis added for effect. I had intended to mention that I was using a car as an example, but meh. Anyways, yes, if you put an engine under undue force, even if it's designed to operate in that manner, just not on that power, the engine will break.

Thought I would raise some points and give my own impression.

It is important to understand that Science is theory, and physics is just a whole bunch of models and definitions, that often use mathematical formulas to define interactions.

There are DIFFERENT and even contradictary scientific theories, especially when you approach theoretical physics. There are simple science things that we can see occur time and time again, where as other science things, cannot be easily duplicated, and require uber tech equipment to demonstrate, that really all you see is data rather than a real effect. If you go back 1000 years magic or supernatural things would be the cause of ;unexplainable phenomenon, now people seem to be to the point that if we have a center point of physical occurance, and we have it as a measurement, and we have a second point that marks the end of that measurement (not just a physical place, but for any dimesnsion of physical existence) then we can define an occurance.

Big occurances may be called body's / entities etc.. It is something in something.

Physics explains 'interaction' or motion within the 'data' of a given dimension. Things like heat and gravity are 'elements'; that cause change in a given body.


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Now a vacuum is an area that matter does not exist in. It is 'closed' to specific types of matter forces, that is it doesn't have a mass, (so gravity does not interact with it) It is like it is invisible to a whole bunch of forces --- it is space. Not all space is a vacuum space, potentially, you see some space we detect, is said to be vacuum space but there are types of energy that we can't see, but theoretically think exist, because it explains some things that happen, in order for those things to happen, that other stuff must exist. (like trying to figure out what a puzzle piece looks like without having the piece, it makes sense it would look like it surroundings, we don't know, but it is the most likely using probabilities (that is really what science is like) but we beleive and 'interpret our experience time and time again.. to happen because.. like, if you were never told about air.. would you know that air existed??? If it is no different than what you always see, how do you know it is there... that is just like vacuum space.


Realize that forces DO NOT exist, they are 'interpreted to exist within energy - different types of energy will contain a different array of POTENTIAL ENERGY, that is that energy.. is the force. For instance friction between two objects may slow them down, but it may also create heat.. why? Because energy is being converted from one form to another. Why is it vibrational enegy? why does it cause heat by vibration.. because energy is released.. energy is heat.

What is gravity (well there has been experiments of artificial gravity creation - if you don't beleive me do a net search. We as of about 3 years ago were at an artificial 'microgravity' stage..

To really understand space you have to understand 'the universe' It is a big ball of energy.. everything is energy.. it is all data of 'INTERCHANGES' in a giant ball of occurance. Vacuum Space is the SPACE between peices of energy.. NOW how do demensions exist? we have width height length (time) and potentially up to about 16 others. (most will be between 7 and 11 or something like that for quantum mechanics (techinically there are infinite demensions, but prooving it may take some time.

anyway the point was that what is space - what is a dimension.. well it is a linear ray (string) of energy. picture it as a line you can't see. (sorta like space) (sorta like time)

now how do you make 2d.. well you put the pencil tip down on the paper and move it.. WHALA!! 2d. what is 3d well now you need to make it cubic (picaso)

ect.. 4d etc.. are things used in math arrays etc.. it ain't more complecated just harder to draw in a 3d reality. much like drawing 3d on a peice of paper is 'virtualized.

That is reality a virtualization resulting from the sensed existance of a point and interaction. That is philosophy though.

VACUUM SPACE IS THUS 1 dimensional occurance that does not intersect with types of matter. It is 'SPACE' between two peices of energy. Not all space is necisarily just space though, some space may just not be able to be detected as some other form of energy. 'dark matter' (and since we only have 15000 years of 15 billion sorta accounted for, and science has only vaugely been around as more than conjecture for more that 500 years.. we may not know everything yet (hell science in itself says. .we are just geussing, this is theory,.. it makes sense this way, god didn't give us all hotties, that type of thing.. atleast now I can make an abomb and get some respect

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Gravity is a force that exists between two bodies (two peice of matter, while there is a universal constant for this (there is no way to really know other than by saying, hell it has worked so far) my theory states that it is due to a larger localized effect (that is each system etc.. will haveit's own gravity that cannot be determined in full because we can't weigh the universe, only someone outside it can.. but like all science this number will get more and more precise (it is related to PI. BUT space itself curves along spacetime.. so we can never have a truely linear occurance in 4d space but we can perceive linear occurance (because we have the mentality to look at it that way.. that is we see flat surfaces - or perceive flat surfaces.. that goes into neurology, but to say the least.. the energy we see.. is NOT identical to all other things perceptions.. we can perceive 'flat' because we can walk into it or otherwise.. but without our sense of touch.. what do we really perceive 'space with colours' we are seeing light.. not matter.. but light the matter isn't necisarily where we see it, reality is a giant hologram of perceived space - of course humans all communicate roughly the same thing (although some people have different biology. It is taken that things are going to be comprehended, 'culturally' we interpret what we can all agree to, because it is how we are socialized. As for space and gravity.. space is a way of saying distance.. or TIME that is time doesn't exist except as the cesium clock - if you look at the evolution of time.. we had daily cycles, lunar cycles, solar cycles, cosmological cycles.. but then the sun dial turned into the water clock, then from the water clock we got 'gears' and then crystals etc.. now it is a pusation of an atom. what is next... if it was easier to measure an electrons movements in any definable pattern, they'd probably be next.. we have moved from looking at our easily seeable measurements to.. very artificial points of trusted reoccurance. Time itself, individually only exists as a moment.. but we as individuals ' miss many moments of thought' other people may think in) for that matter.. every moment of though is likely someone elses moment.. that is the more thoughts there are.. in 1d space.. that is 1 moment of time. but 3d space has many moments of occurance at the same time (that is time in space) for every extra dimension, a lot more stuff happens, if it is the same size plus any extra arrays cluster points.

back to what I was saying about gravity though
meanwhile there are also 'localized gravity' occurances.. these are due to the mass of objects

that is gravity at one point of the earth will be felt at a different ammount than another part of the earth, because of how close we are to mass.. we are either falling or climbing or something like that through space. The closer we are to big stuff, the faster we fall on earth this is limited due to terminal velocity (atmospheric things and such) in space it is sorta the same, but there is much less STUFF to slow us down. Outer space isn't all just void space (I like the use of the word void space as opposed to 'vacuum space' .
There is a lot less resistance, and nothing to stop most energy and matter from moving without 'change', that is there is nothing acting on the matter and energy over that area. Thing can still hit one another.. but the space itself is just 'time' of continuance (a continuum) It also can be represented as 'distance.. because distance... as far as a meter for instance isn't actually measure by taking a meter stick.. it isn't tied to a physical object.. in SI it is tied to.. how far energy travels in a really short period of time.. thus our distance measurement is actually a measurement of how fast light travels in the space time continuum. Time itself.. is a guess that we can all agree on, by what we perceive to be (sorta philosophical) things get wonky at that point but the engineers keep making the stuff to get the sciencetists the prestige to get the women. (And or men whatever)

Gravity is sorta a way of saying what way energy is... cause energy goes to the most energy at the lowest temperature (That is it is slowing down into a solid form) the hotter stuff is.. the faster it moves away from other energy..

the catch being there is a threshhold for how much energy.. can exist close to each other.. when it combines.. it heats (due to mass collapse) and then the center turns into molten stuff like the sun... eventually starts blow up, it takes a whole bunch of time and it all comes back together.. the big bang and crunch stuff is a little wonky, and why it started or if it'll ever end is mostly redundant cause it ain't logical, and science is religion, pedagogy, without logic.


Stuff accellerates because it is drawn to another point (it is pulled) hot stuff is pulled to lighter things, while cold stuff is pulled to heavier things.

accelleration is a representtion of energy being transfered between two points. for instance when we are driving a car, the more wheel rotations we do the more the vehicles moves.. this is because the car is applying thermochemical energy to cause pistons to be driven (which then converts the energy to kinetic energy) now what about an airplane.. well basically an airplane 'pushes air' or pulls itself on air... drag is air that pulls the plane down while lift pulls it up. it is the force of moving the air that allows the plane to fly (that and other aerodynamic properties) heating air with a jet.. lets the plane push the air behind it really fast this allows the plane to acheive lift with a propeller it is actually a turbine effect and then wind goes under the wings and forms an air cushion etc.. while in space.. basically what is used IS MASS.. to create push.. bits of ionized energy (atoms or whatever) are dropped out of the back of the iondrive.. this causes 'a push from the ion to occur each atom gives a little push. BUT in void space.. there is nothing to slow it down.. (of course there are gravity effects..in the solar system until you get out past planet x etc..) so you just keep on accelerating. acceleration and speed are not the same thing.. that is how fast you go does not mean how fast you will continue to go.. acceleration ADDS to how fast you go.. but on earth friction and other effects slow you down.. on ice when skating.. there isn't as much friction.. so you can go faster without doing anything beacuse you have energy invested in your movement. that is you accelerated yourself.. now you get to slide.

velocity would continue to climb, but there are relative limits to how fast you can go without slipping into a different frame of time..................., this isn't necisarily true, but most relativists will agree. The 'yah time slows down then reverses when you go faster than light.. it is an intersting idea.. but it causes.. paradoxial issues.. BUT the only way to assume it is.. we don't remember time we change. of course there will always be the how far does it go and .. what is outside the box and a bunch of other primes and beleif issues... I personally beleive, realiity is not a logical entity.. it is illogical, and that anything that defies logic, is nonsensical, and cannot bring about any logically reasonable use, beyond the point of agreeing illogic does exist in reality, and it cannot be defined logically. I have my faith in illogic, (chaos) and I myself am representative of an interpretation of order (logos) My core is chaos, but time and all the other entities (formerly gods) allow me to be an experience of existance, a representation of divinity. a muse. I myself am that divinity as I am chaos, but it is chaos seeing their children, and experiencing our existance, in chaos, ourself. That is a little off science though.



"Let's say an object in space is travelling nearly at the speed of light. Some kind of force (for example gravity) makes it accelerate. Why can't it reach the speed of light?"

We are already traveling the fastest we can.. it is just how fast we travel towards something.. our conversion .. of energy. We are changing our relative position to other bits of energy.. that energy is also moving towards something else.. we can only go as fast as we are going to the common conversion point.. and so on.. using triumerative.

I could go on, but I think that that shares my view of what others already touched on..

good info on accelleration and friction.

1) There's nothing there. Sound cannot travel because there is no medium for it to travel in.

2) There's nothing applying a backwards force. For example, on earth a car decelerates because there's friction. A constant velocity is when the forces acting on an object all cancel each other out. When in space, there is nothing to cancel the forwards speed out (unless you crash into something, I guess), so you constantly keep going. However, mathematically you can never reach the speed of light.Well, therotically that is due to the fact that light is basically the essence of enregy, but if one can transfer matter to energy then you can do it some people theorize.

Well, therotically that is due to the fact that light is basically the essence of enregy, but if one can transfer matter to energy then you can do it some people theorize.

I agree, that's true. Reminds me of Back to the Future. Heh, Jiggawatts.