About gravity

So, if I understood it, in a flat earth, if i jump up, i dont go back, but the earth comes to me, because its travelling at 1g? I want a simple answer yes or no, if no, what is the definition?

I believe yes.

Well, then, if I am correct you would feel no or very little force when coming back down.Try with a pen.Throw it up and catch it in the hand.Now throw it up and follow it with your hand and hold it.You feel the difference?

Well, then, if I am correct you would feel no or very little force when coming back down.Try with a pen.Throw it up and catch it in the hand.Now throw it and follow it with your hand and hold it.You feel the difference?

Wow, this actually makes sense to me.  If the earth came to you, then the feeling of jumping would be way different.  It'd be like, the acceleration of going up, and then being caught.  Not the acceleration of going up, than the acceleration of going down.  But I'm sure there is a obvious hole in this somewhere that a FE'er will find.

Yes, it does make sense, doesn't it? I'm quite curious how are they gonna explain it

When you allow the pen to fall, it accelerates towards your hand.  When you follow it up, it does not accelerate relative to your hand.

On the flat Earth, when you jump, the Earth accelerates up towards you, much like the pen accelerating towards your stationary hand.  It does not simply follow you up -- it speeds up as it approaches you.

Thus, the situation is more analogous to the scenario when you left your hand stationary than when you followed the pen.  In other words, you would feel a "force" when coming back down (what you actually feel when the ground hits you, or when the pen hits your hand, is a transfer of energy: the kinetic energy of the Earth/pen deforms your body, and you feel the deformation).

When you allow the pen to fall, it accelerates towards your hand.  When you follow it up, it does not accelerate relative to your hand.

On the flat Earth, when you jump, the Earth accelerates up towards you, much like the pen accelerating towards your stationary hand.  It does not simply follow you up -- it speeds up as it approaches you.

Thus, the situation is more analogous to the scenario when you left your hand stationary than when you followed the pen.  In other words, you would feel a "force" when coming back down (what you actually feel when the ground hits you, or when the pen hits your hand, is a transfer of energy: the kinetic energy of the Earth/pen deforms your body, and you feel the deformation).

Very nice said, but I don't think that it prooves a point.So you are saying that the flat earth is accelerating faster towards you when you reach the peak of the jump,( that is the start of coming back on the round earth).True, but do it with a pice of paper, or leaf.When it falls down it goes left and right and moves a lot in the air and thus comes down slower.So if you throw a brick and a paper at the same time the paper would fall later.But in the FE it would touch the ground at the same time, because the earth is going towards it and there would be no wobbling in the air.

Your pen analogy is flawed. When you throw a pen in the air, it is the gravity of the round earth that decelerates it, and brings it back to your hand. In the flat earth theory, there is no external gravity, so the pen would continue going upwards, and your hand would have to accelerate upwards to catch it. When you move your hand upwards with the pen in your version, the pen is being slowed by gravity so the feeling is different. This would not happen.

On the flat Earth, when you jump, the Earth accelerates up towards you, much like the pen accelerating towards your stationary hand.  It does not simply follow you up -- it speeds up as it approaches you.

And explain this a bit more.How come the flat earth doesn't follow you?It just sits and waits when you jump?It goes at a constant speed.And when it speeds up when it approaches you, you would still expirience a force like something pulled you upwards not a force like you fell onto something.


Oh and if the earth goes at 1 g speed, does that mean you would have to jump at a speed higher than 1 g to move your feet from the ground?

So you are saying that the flat earth is accelerating faster towards you when you reach the peak of the jump,

No.  Its acceleration is constant.

So if you throw a brick and a paper at the same time the paper would fall later.But in the FE it would touch the ground at the same time, because the earth is going towards it and there would be no wobbling in the air.

What do you think happens to the air?  The Earth pushes up on it, just like it pushes up on your feet while you're standing on it.  The air then pushes up on the paper and the brick, and this affects the paper to a very large degree, but the brick to a much lesser degree.

How come the flat doesn't follow you?

I didn't say that.  I said,

It does not simply follow you up

i.e., it does something else besides following you.

And when it speeds up when it approaches you, you would still expirience a force like something pulled you upwards not a force like you fell onto something.

Why would you feel a force like something pulled you upwards?  In the model I'm describing, nothing is pulling you anywhere -- the Earth is accelerating.

Oh and if the earth goes at 1 g speed, does that mean you would have to jump at a speed higher than 1 g to move your feet from the ground?

You mean "acceleration", not speed.  You need to accelerate upwards relative to the Earth, at some positive rate.  It doesn't have to be greater than 1g relative to the Earth, but it would have to be greater than 1g relative to an inertial reference frame in which the Earth is moving slowly.

Well ok that stays the same then. What about the other questions?

Round earth- you fall jump, gravity pulls you back

Flat earth- you jump, thus move upwards at a faster rate than 1g( which is impossible)

If an acceleration of more than 1g was impossible gun barrels would be miles long, anyone could go into space, and roller casters would be useless. But still, in order for a constant acceleration on earth to sustain gravity you would need masses and masses of energy, if earth is billions of years old then we're talking astronomical energy, more than could be supplied by anything smaller than earth.

in order for a constant acceleration on earth to sustain gravity you would need masses and masses of energy, if earth is billions of years old then we're talking astronomical energy, more than could be supplied by anything smaller than earth.

Supposedly, according to our admittedly-limited understanding of the laws of physics.

If an acceleration of more than 1g was impossible gun barrels would be miles long, anyone could go into space, and roller casters would be useless.

Read my whole sentence, I didn't say 1g is impossible I said that a man can't jump at a speed of 1g

Why would you feel a force like something pulled you upwards?  In the model I'm describing, nothing is pulling you anywhere -- the Earth is accelerating.

It is accelerating towards you, so when you touch the ground, you expirience a force, a force like you were pulled, not one like you fell,as it is supposed to be (we clearcly do not understand each others point of view )

If an acceleration of more than 1g was impossible gun barrels would be miles long, anyone could go into space, and roller casters would be useless.

Read my whole sentence, I didn't say 1g is impossible I said that a man can't jump at a speed of 1g

It is accelerating towards you, so when you touch the ground, you expirience a force, a force like you were pulled, not one like you fell,as it is supposed to be

It would not be possible to distinguish between those two feelings, even if what you said were accurate.  If somebody throws a book at you, when the book hits you, I don't expect you will feel like you were being pulled anywhere.

No, but that isn't the same thing as jumping and the earth collecting you

No, but that isn't the same thing as jumping and the earth collecting you

not by much.

What about the part of feeling "lighter" (not sure how to say it) when you come down.

What about the part of feeling "lighter" (not sure how to say it) when you come down.

If you do not feel a force on yourself then you are technically weightless.  Weight is a force.  When you are falling after you jump the surface of the Earth is not exerting a force on you. 

Question. If everyone on Earth jumped on one side of the planet, would it flip?

I think that happened on Tuesday.

It makes sense now.

Your pen analogy is flawed. When you throw a pen in the air, it is the gravity of the round earth that decelerates it, and brings it back to your hand. In the flat earth theory, there is no external gravity, so the pen would continue going upwards, and your hand would have to accelerate upwards to catch it. When you move your hand upwards with the pen in your version, the pen is being slowed by gravity so the feeling is different. This would not happen.

I would just like to say that there is no such thing as "deceleration."  It's still acceleration, just in different directions. 

Quote from: Hturtfothgileht on April 01, 2007, 02:06:16 PM

Your pen analogy is flawed. When you throw a pen in the air, it is the gravity of the round earth that decelerates it, and brings it back to your hand. In the flat earth theory, there is no external gravity, so the pen would continue going upwards, and your hand would have to accelerate upwards to catch it. When you move your hand upwards with the pen in your version, the pen is being slowed by gravity so the feeling is different. This would not happen.

I would just like to say that there is no such thing as "deceleration."  It's still acceleration, just in different directions. 

Yes there is.

Quote from: EvilToothpaste on April 02, 2007, 08:23:43 AM

Quote from: Hturtfothgileht on April 01, 2007, 02:06:16 PM

Your pen analogy is flawed. When you throw a pen in the air, it is the gravity of the round earth that decelerates it, and brings it back to your hand. In the flat earth theory, there is no external gravity, so the pen would continue going upwards, and your hand would have to accelerate upwards to catch it. When you move your hand upwards with the pen in your version, the pen is being slowed by gravity so the feeling is different. This would not happen.

I would just like to say that there is no such thing as "deceleration."  It's still acceleration, just in different directions. 

Yes there is.

No, there isn't. 

Quote from: EIRD on April 02, 2007, 08:25:19 AM

Quote from: EvilToothpaste on April 02, 2007, 08:23:43 AM

Quote from: Hturtfothgileht on April 01, 2007, 02:06:16 PM

Your pen analogy is flawed. When you throw a pen in the air, it is the gravity of the round earth that decelerates it, and brings it back to your hand. In the flat earth theory, there is no external gravity, so the pen would continue going upwards, and your hand would have to accelerate upwards to catch it. When you move your hand upwards with the pen in your version, the pen is being slowed by gravity so the feeling is different. This would not happen.

I would just like to say that there is no such thing as "deceleration."  It's still acceleration, just in different directions. 

Yes there is.

No, there isn't. 

Deceleration: A rate of decrease in velocity.

It exists in the dictionary.

From a physics standpoint there is no such thing, as there is no "absolute" frame of reference to which one can "decelerate." 

Also, 'ac' is a variant of 'ad' (as in advance) and it is not appropriately negated by 'de'. 

From a physics standpoint there is no such thing, as there is no "absolute" frame of reference to which one can "decelerate." 

Also, 'ac' is a variant of 'ad' (as in advance) and it is not appropriately negated by 'de'. 

Ok...then when would it be used if not in physics.

It's just a self-reference err similar to how you can't "pull" anything (except with a magnet).  We accelerate forwards, decelerate backwards.  We push away from us and pull towards us.  We say we are 'pulling', but really we are pushing.  For example, I put my fingers on the sides of a cube and pull but really I am pushing the cube towards me with the help of friction. 

One can only decelerate until a zero velocity is reached (in whatever field of reference one has chosen), then acceleration is again happening.  From the 'stationary Earth' frame of reference your car is decresing in velocity when you push the brake, and it has a negative acceleration.  From the 'moving' car, though, you feel an increase in acceleration because in that frame you have no velocity. 

It's convenient to use 'deceleration' only if the socially accepted convention applies to the situation.  In driving your car to the mall it works, but not in engineering and physics; you'll end up designing something that doesn't work, or make an argument that is not valid.