Round earth Gravity vs. Flat earth "Gravity"

Apollo...Did you read the rest of this thread, or just jump in?   Seriously, before defending the stupid concept of "the jet-pack" theory in a thread that disproves it, read the thread.

TofuGlove you are correct on all points, and by performing just the experiment you suggested we can show that is in fact universal gravitation, and not acceleration, that governs the motion of object on earth surface, and that the earth is a sphere. The experiment can even be done without leaving sea level, simply stand over a gold (or any heavy metal) deposit. The scale will read more weight (a very small amount) because the increased density of mass over which you stand will have a larger gravitational attraction then normal soil, if fact this is one way to survey for precious metals.

The reason for my previous post was simply to clarify the fundamentals of acceleration and constant motion, with a small aside to the debate.

And 6strings I did read the post, and unfortunately you did not disprove my point as you primary argument (the “floating leg”) if fundamentally flawed, and the “stupid” jet-pack theory is actually how things work. Allow me to explain.

If we place you on the accelerating disk you move, and accelerate along with it, by Newton’s laws F=m*a, this is only possible if there is a force being applied to you as well as the disk its self. How this is accomplished is the disk exerts what is called a normal force against. This force is proportional to you weight and in the up direction so you will accelerate at the same rate as the disk. When you lift your leg you remove the normal force that was acting on your leg, so in turn you must provide the force necessary to maintain you leg at that acceleration. If your leg happened to have a mass of 1kg the force needed would be F= 1kg * 9.81m/s^2 or 9.81 n. the moment you fail to provide this force by say, relaxing your muscles the leg moves at a constant rate and is overtaken by the disk. Or to an observer on the disk you leg simply falling back to the “ground”.

For a simpler example: when accelerating very quickly in a car you will feel not only your torso but all your appendages (arms, legs) being pushed towards the back of the vehicle. Try it for your-self. To say it would be any different on the accelerating disk is logically fallacious.

No Apollo.  Now you fail.  I can stand peopple misunderstanding my point, or taking issue with a point that's debatable, but you just don't understand the physics of this.  I thought you would given your post on impulse, but apparently, your knowledge only extends that far.  Let's break it down, shall we?

You lift your leg.  Say the leg has a mass of 1 kg, like you said.  This requires 9.8 N of force. Your leg is now lifted.

If you release your leg muscles, and force is pulling down, the leg falls, because the force pulling down now exeeds the force pulling up.

But If the earth is a disk, rushing up, my other leg, planted on the ground, causes the rest of my body to continue accelerating upwards at 9.8 m/s^2, including my lifted leg.  Because the ground would be pushing my leg which I assume is still connected in the same proportions to the rest of my body, upwards.  I'm also making the assumption that the ground underneath my upraised leg isn't accelerating faster to compensate, because, frankly, that would be stupid.

Now, Apollo, if two objects are X meters away from each other, and both accelerate at 9.8 m/s^2, when do they encounter each other?  They don't.

So yes, the "jet pack" theory is stupid, don't put quotation marks around the word "stupid" to make it seem as though I'm being intolerant, it's just flawed.

Now, while I'll admit that adding math gives your posts a certain feeling of authenticity at first glance, don't use it if you can't properly apply the math.

Just to clarify the used the quotation marks to indicate that it was the word you used and not I. I would not presume to label you as anything.

There still is a misunderstanding. When I said the disk will overtake the free leg I did not mean to imply that one side of the disk is moving faster, because that is stupid. What I should have said is that the lifted leg, with no force being applied to it, would be moving at a constant speed relative to the rest of the body, and as such would straighten out and return to normal posture. The issue I have with your argument is that by saying the up-raised unsupported leg would be accelerating with the rest of the body, you imply that if one portion of the body is accelerating it means all are (see below*). Now I will say that the normal force that a being applied to the other leg will accelerate the leg, the pelvis and the trunk at the same rate as the disk but the up-raised leg, if left flaccid, will have no force applied to it at any other spot then the hip joint. Which would do nothing more then keep the leg in its socket.

Imagine I’m hovering in space un-moving. I hold my arm out to the side and glue my hand to a weight that about as massive as a planet. The disk comes at me accelerating at some rate. When it hits me, the edge of the disk connects with my shoulder so that my arm hangs off the side. Assuming that I cannot let go of the weight, and my body is stuck to the disk, what will happen?

My view: as the disk accelerates my body, my arm experiences no normal force and therefore does not accelerate. The end result: my arm is ripped out of its socket still holding the weight as I cannot apply enough force for my arm to accelerate the massive load.

My interpretation of your view: As the arm and weight is now part of my body, as the disk accelerates me I need not apply even the smallest force to more the weight since the whole length of my arm accelerates with my body regardless.

I’m sorry but that second option does not sound possible to me. Did I not understand it as you intended?

Ahhhh...I see, I misunderstoof your original point.  And you're quite correct, insofar as you state that my leg would "fall" to the ground.  However, you're wrong when you state that this example doesn't disprove the "jet pack" theory.  I merely didn't follow it to it's logical conclusion, which does disprove it.

While a push up, and a pull down would produce the same result, their effects on our bodies wouldn't be the same.  The rising earth model would mean our leg would be pulled into its extended position by the rest of our body moving up at 9.8 m/s^2, however, this would require all the stress of this pull to be exacted on the leg from the socket, which would cause the tendons to extend, as a result of the pressure.

However, this doesn't happen, we'll notice that the force is evenly distributed along the leg (actually, more focussed towards the lower end of the leg), as could only occur if there is a downward force pulling the entire leg down.

My point still stands (although admittedly, slightly altered)

The falling-leg phenomenon is perfectly explained by a rushing-up-Earth theory of gravity.  The Earth pushes the supporting leg, the supporting leg pushes the body, and inertia keeps the free leg in place.

For a demonstration, take a hard-cover book.  Books with thick, heavy covers and aging, loose binding are better.  Hold the book with the front cover facing the ceiling.  Grab all of the book in one hand except for the back cover, like, thumb on front cover, fingers grasping the last page, so that the back cover falls, dangles, swings back and forth for a second or so and comes to rest.

That's the setup.

Now, quickly push the book towards the binding (so if you were holding it in your right hand, with the front cover up and the binding to the left, you'd be pushing it to the left).  Note what happens?  The free-swining back cover swings towards your hand.

By analogy: the Earth is your hand, your standing leg + body are the front cover and pages, your free leg is the back cover, and up is left.

-Erasmus

The cover would fall because of air resistance and gravity acting on it. Here, there is no gravity and the air is theoretically being pushed as well so it is undisturbed. So, where is the other force that would cause the leg to fall? What resistance does it meet to not allow it to continue to rise with the rest of the body?

BTW, it's late, so I'm going to sleep. You'll have to wait until tomorrow before I can destroy the rest of your posts.

Again, nothing makes the leg fall / book cover swing.  The leg/book cover stay in the same place, and everything else rushes up/to the left.

If you don't like the hardcover book analogy, bring something that you can use as a pendulum next time you're in a moving vehicle.  When the vehicle accelerates, the pendulum will swing in the opposite direction -- *against* air resistance in this case.  Nor is air resistance the explanation for the swinging book cover in my example.  The only thing that explains it is inertia.

-Erasmus

Yes, and I expalined why that doesn't work in my last post. When you lift your leg, it bends, right (I'm assuming you lift it like a normal person would)?  Now, of course your body rushing up would cause streching in the tendons in your upper leg, in turn causing streching in the tendons in your lower leg, resulting in your leg falling as it normally would on the round earth.

However, we note that when our legs fall, force and stress are not solely isolated on our upper leg's tendons, but rather evenly spread out along our leg (actually, more focused near the lower end of the leg).  Following this to it's logical conclusion, we can assume that there is a downward force, pulling this down.

Apollo and Erasmus were quite right when they stated the leg would fall, hoever the mechanism by which they would do so isn't the same.

I move that the sensations you have in your leg during its short-duration fall after you relax your muscles are not useful as evidence.  The stretch receptors in at least six different muscle groups are involved here, some of them (hamstrings and quadriceps) much stronger than others (er, calf muscles).  It's plausible that when you "relax" all the muscles, it's not done equally, resulting in feeling that a pull is beginning near the foot, where the weaker muscles lie.

Even still, the reason you feel forces throughout the leg is because the hip pulls the thigh (so you feel stress on the hip), the thigh pulls the calf (so you feel stress on the knee), and the calf pulls the foot (so you feel stress on the ankle).

Also, if your put your arm straight up in the air, and then relax it, by an argument similar to yours we would expect all the "pulling" to happen at the shoulder, which would... be strange.  Would my whole body be pulled to the ground?  Usually when you pull from the "forward" end of a long object, the object stays in line, or lines up with the force if not already in line (e.g., your relaxed leg being pulled from below lines up with gravity).  However, the arm kind of crumples at the elbow and then swings around.  Unfortunately, I find I cannot fully relax my arm to the point where all its motion is explicable by gravity: I realize that resting-state muscle tone still accounts for some forces on the very complex pendulum that is the arm.

The complexity of body mechanics leads me to suggest that a better experimental object is the simple pendulum.  From any initial starting position, the pendulum will swing towards a force that pushes its pivot, and away from a force that pulls its pivot.  This is what my hard-cover book experiment is supposed to demonstrate; something more like an iron ball on the end of a stick would be better since then air resistance would be much less of an issue.  You might tright loosely holding a pen or pencil vertically from one end between two fingers and moving your hand from side to side: the pen will swing in the opposite direction of your hand.  And of course, a pendulum suspending inside an accelerating vehicle is an excellent demonstration: since the air inside the vehicle is at rest w.r.t. the vehicle, any swinging of the pendulum will be *against* air resistance.

I move that the sensations you have in your leg during its short-duration fall after you relax your muscles are not useful as evidence. The stretch receptors in at least six different muscle groups are involved here, some of them (hamstrings and quadriceps) much stronger than others (er, calf muscles). It's plausible that when you "relax" all the muscles, it's not done equally, resulting in feeling that a pull is beginning near the foot, where the weaker muscles lie.

Granted, but the stress is measurable by modern medicine.  I've actually had this done on me after breaking my leg in several places, the doctors had to measure the streeses on the tendons in my legs, and they do occur simultaneously.  I can assure you that my explanation of what does happens and what would happen are wholly correct.

Right, but what you claim happens is still explained by a pushing-up model of gravity.

To recap,

Even still, the reason you feel forces throughout the leg is because the hip pulls the thigh (so you feel stress on the hip), the thigh pulls the calf (so you feel stress on the knee), and the calf pulls the foot (so you feel stress on the ankle).

Before you respond, "Ah, but that's not simultaneous," you must realize that it is.  All parts of your leg (or the pendulum in my example) that are not fully supported by the accelerating object will tend to continue moving at the same upwards speed; that is, to not accelerate.  They will all, simultaneously, tend not to accelerate, and thus appear to fall down, simultaneously.

Wikipedia has a very rigorous exposition of how acceleration and gravity are indistinguishable.  See http://en.wikipedia.org/wiki/Equivalence_principle.

And despite your doctors' tests, I still claim that the human body is too complex a system for use in discussions on mechanics.  Without meaning to impune their expertise at all, they were not trying to answer the same sort of questions we are.  Furthermore, some on this forum might claim that they are lying to you to keep you in the dark about the true nature of gravity and the geometry of the Earth.

-Erasmus

Hmm...that's all true...doesn't really matter though, the "jet pack" theory is still stupid, given that E=mc^2 and the speed of light is constant.  Ergo, maintaining this acceleration would be impossible, as we can all agree that the earth has mass.

E=mc^2 and the speed of light is constant.

This is exactly why I'm trying to get some consensus on what sorts of physics are acceptible.  The idea that the speed of light is constant is at least partly based on experiments that were done assuming a Copernican model of the solar system; esp. that the Earth is nearly spherical and orbits at a great distance around a fixed sun through the near-vacuum of space.

The speed of light is in fact *not* constant.  If you make it go through different materials, it may slow down.  Only if you assume that light's wavelike nature does not require a medium to transmit the wave energy (usually called "aether") does much of modern physics make sense.

I propose that we only accept the sort of physics that the everyday person can verify himself, without relying on the "establishment" for guidance or resources.  Otherwise, anybody who claims the government is lying to us about photos of Earth from space can just as easily claim that the faculty of the Institute for Advanced Studies at Princeton (e.g. Einstein) is in on it as well.  Thus, I suggest that no arguments of the form, "A recognized authority in the relevant field assures me that E=mc^2 and the speed of light is constant," because flat-Earthers are probably already refusing to recognize such authorities.

That being said, it's possible to get a constant acceleration and still maintain a finite speed (less than that of light).  In general, there's a really "straightforward" way of "getting around" the constraints of special relativity.  Heheh.

-Erasmus

Ok 1-

In general, there's a really "straightforward" way of "getting around" the constraints of special relativity. Heheh.

That's not funny.  Stop it.

2-

. Thus, I suggest that no arguments of the form, "A recognized authority in the relevant field assures me that E=mc^2 and the speed of light is constant," because flat-Earthers are probably already refusing to recognize such authorities.

We've established that the "A recognized authority in the relevant field assures me...", isn't tenable.  Do your homework.  And, if you demand, I will work E=mc^2 out for you from first principles.
The speed of light being constant/not dependant on aether, may be more difficult, but I could attemp that too.

Also,

I propose that we only accept the sort of physics that the everyday person can verify himself, without relying on the "establishment" for guidance or resources.

Done already, you're just rehashing old points that have been made ad nauseum.

Do your homework, cause you really aren't proposing anything new here.

First off, I would like to thank Erasmus for making the argument far better then I ever could.

Secondly, I wrote the jet pack explanation only to demonstrate that acceleration is indistinguishable from gravity, at least on the scale an unaided human can observe. I was not trying to “prove” the earth rushing up model. For purposes of the jet pack explanation just assume the acceleration began only moments ago, thereby eliminating any concern about special relativity.

If you need another example to fill in your understanding take this one, it should show that the sensation on your body of gravity and acceleration are identical.

Imagine you’re in an iron box, should it suddenly accelerate you would be thrown to the opposite wall. Not being able to observe the outside from within, you might proclaimed “something pushed me into the wall” rather then “the box moved” as you have no way of knowing. This is exactly like your seat-belt caching you as you decelerate. If you were not aware of the cars motion you might conclude something pushed you into your seat-belt.

So, getting back to the not-new thing that I'm not proposing.  The speed of light is not a problem.  As the Earth accelerates, it will appear to an outside observer, it will gain relativistic mass, so it'll appear to get heavier, which causes its acceleration to decrease.

Of course, from the perspective of somebody on the jet-pack Earth, no changes occur; gravity appears constant.

Fortunately, flat-Earth theory asserts that nobody has ever had an outside perspective on the Earth -- or nobody's coming forward to tell the tale.

Long story short, the jet-pack theory does not violate any physics -- at least, nothing related to E=mc^2 or anything in that vein.

The other problem with the speed-of-light rebuttal to the jet-pack theory is that it assumes there to be some global frame of reference with respect to which the speed of the Earth is being measured.  This is one of the most common mistakes among those unfamiliar with relativity.

So, what were the other disagreements?

-Erasmus

Try this experiment:
-Stand up
-Lift your leg
-Release all the muscles in your leg

Notice how your leg falls to the ground?  Iff the earth were rushing up, this wouldn't happen, because your other leg would act as a brace between the ground and your body.  Meaning your leg should float.  It doesn't.

QED.  Gravity is not the result of the earth rushing upwards.

Anyone care to explain to me why I'm wrong?

6strings, your reasoning is not right.
Your rised leg would not go towards the ground if you were a rigid body, but as you aren't rigid, there is something called inertia, and if the flat-Earth ground were accelerating, your rised leg would go toward the ground because of the inertia, the same effect that the round Earth gravity produce.

In fact, acceleration have the same effect of gravity from the point of view of the accelerated observer.

Einstein said that a long time ago: http://en.wikipedia.org/wiki/Equivalence_principle

I have a question about so called flat earth gravity simmilar I think to 6 strings.
Alright according to flat earth theory the earth is rushing upwards at 9.8meters per second correct? Okay assuming that is correct how do you explain helicopters?
I personally have seen helicopters hovering just of the ground for longer than a second. If flat earth gravity was correct wouldn't the earth rush up to meet the helicopter?
Also why is it that so many flat earthers bash round earthers for having faith in something we cant see or touch ike gravity when many of them are religious fanatics?
Not to bash religion as I'm a devout Catholic but faith in God requires the ability to believ in something you cannot see and touch with many less observable conseuences than gravity.Its odd.

Anyway I'd like helicopters to be explained to me under flat earth gravity?
Note neither magic nor atmspheric phenomenon are explanations

An bemused
Cinlef

It is the same, hellicopters are continuosly producing an acceleration towards the sky because of the spinning of the blades in the air, so the acceleration of the flat-Earth is equated the the acceleration of the hellicopter toward the sky.
If the hellicopter acceleration is greater than the flat-Earth acceleration, then it goes up, if not, then it goes down. When it is the same, if stays suspended.

No, the flat earth contention seems to be that the air flows up/is pushed up with the ground.

So the atmosphere is only 150 feet tall?
Because if it was taller, the air would escape over the 150 feet ice wall at the flat-Earth edges...

Quote from: "6strings"

No, the flat earth contention seems to be that the air flows up/is pushed up with the ground.

So the atmosphere is only 150 feet tall?
Because if it was taller, the air would escape over the 150 feet ice wall at the flat-Earth edges...

good question.

So, getting back to the not-new thing that I'm not proposing.  The speed of light is not a problem.  As the Earth accelerates, it will appear to an outside observer, it will gain relativistic mass, so it'll appear to get heavier, which causes its acceleration to decrease.

Please do not absue the theory of relativity in this way.

If there was an outside observer and to that observer the earth was accelarating at 9.8 ms-2.

Then yes the earths relativistic mass would increase and because a = f/m
teh accelaration would decrease. This presents 2 problems.

1. Where does the F come from? ie what is there that is pulling or pushing the earth with enough force to accelarte it at 9.8

2. This kinda ruins your theory of 'gravity' as the accelration decreases then this would also mean your gravity would decrease so as speed of earth -> C  mass of earth -> infinite   accelaration -> 0 and gravity ->0

oh noes!

OOH.

Factual science BURNAGE!

Please do not absue the theory of relativity in this way.

If you are accusing me of lying, then I challenge you to a duel.

1. Where does the F come from? ie what is there that is pulling or pushing the earth with enough force to accelarte it at 9.8

Flat-Earthers haven't offered an explanation of the source of the upward force, either.  I'm starting with "suppose we have a constant upward force" and going from there.

2. This kinda ruins your theory of 'gravity' as the accelration decreases then this would also mean your gravity would decrease so as speed of earth -> C mass of earth -> infinite accelaration -> 0 and gravity ->0

Nonono, physics guru.  You forget how we measure gravity: not as acceleration, but as force.  Remember learning about inverse proportions?  In this system, mass and acceleration are in inverse proportion.

Suppose you were right; that gravity would decrease as t -> infinity.  You're saying I, standing on the surface of the upward-rushing Earth, would measure a 1 kg object as asymptotically less and less over time?  But then surely, I would notice the difference in weight, and proclaim, "Aha!  Since the weight of my 1kg object is decreasing, I can conclude that I am only *perceiving* gravity, but that what is *really* happening is acceleration!  Foolish Erasmus!"

And then I would remember the principle of equivalence, that under no circumstances may I make such a distinction.

If you're not convinced, apply equivalence in the other direction.  What you're saying implies that if I stood on a bathroom scale (on a round Earth in the commonly accepted model), over a long period of time I would notice my weight decreasing.  For reasons other than the fact that I haven't stopped to eat or drink.  Hmm, interesting.

"Oh don't give me no more o' that Ol' Principle of Equivalence."

Oh yes.

-Erasmus

Just because I'm sure everybody's confused, I proclaim that I believe the jet-pack theory to lack all merit (not that I've ever claimed otherwise), but *only* because of physicsguru's Problem 1 ("Wtf is F?"), not because it doesn't explain observations.

-Erasmus

2. This kinda ruins your theory of 'gravity' as the accelration decreases then this would also mean your gravity would decrease so as speed of earth -> C mass of earth -> infinite accelaration -> 0 and gravity ->0

Nonono, physics guru.  You forget how we measure gravity: not as acceleration, but as force.  Remember learning about inverse proportions?  In this system, mass and acceleration are in inverse proportion.

 Well, to put this down to your obviously challenged knowledge of physics;

AS we are doing a slight jot off of the speed of light, this means we have a mass a slight jot of of an infinite one. presuming that our mystery force is constant, then our acceleration must have basically stopped

gravity is either measured as N kg-1 or as m s -2

but the gravity im using in that point is the gravity of the mystical flat world which is casued by our disc accelarating through space i am pointing out that as our mass increases towards infinite our accelaration must also lessen so this apparent gravity caused by accelaration must also lessen.



 unfortunately it doesnt.

AS we are doing a slight jot off of the speed of light, this means we have a mass a slight jot of of an infinite one. presuming that our mystery force is constant, then our acceleration must have basically stopped

So what?  Like I said, we don't perceive acceleration; we perceive force, which is the product of mass and acceleration.

Look, I'm getting tired of ad hominem arguments.  If you think my understanding of physics is incorrect, explain the error in my thinking.  Don't simply ignore my entire post and then repeat something that I've already said I don't agree is the right way to be thinking about things.

If you think I'm wrong when I say, "We're not measuring acceleration, we're measuring force," then explain to my why I'm incorrect.  If you agree with that statement, then point to some other flaw in my argument.  But it has to be a flaw *in* my argument, not just some *other* statement that you believe is true.

-Erasmus

The speed of light is in fact *not* constant.  If you make it go through different materials, it may slow down.  Only if you assume that light's wavelike nature does not require a medium to transmit the wave energy (usually called "aether") does much of modern physics make sense.

-Erasmus

the speed of light is constant.  If you change the variable (i.e. sending it thru different media) then you usually slow down the constant speed of light (in relation to a vaccum, aka space, aka aether).

I'm assuming you are aware of "wave-particle duality" and tacit understanding of quantum physics.  

Modern physics makes sense if you accept these developments in science.

Modern physics makes sense if you accept these developments in science.

I'm suggesting that flat-Earthers may be required *not* to accept developments in science if they want a coherent theory.

-Erasmus