Looking for an intelligent argument. (Terminal Velocity)

I did.  You haven’t answered my attacks. 

Really?

Do you know what "motion along geodesic" is?

He is not falling, nor is he free of external forces.  It is impossible for him to be in free fall. 

He is moving along geodesics (free fall), but the mechanical resistance of the Earth (or his chair) disallows that. Is this really that hard for you to understand?

Astronauts are free of forces.  Not even close to the same thing. 

Obviously. However, we aren't, because there is an upward force under us due to mechanical resistance.

Quote from: cbarnett97 on August 20, 2008, 12:15:04 AM

your equation is correct with real life results but it does not relfect the FE model states. so when I ask you about the FE model you are so very wrong

Did you forget the part where I said that I derived it according to the FE model?

then you need to get a better understanding of the FE model

I understand it perfectly well.  You are the one that needs to get a better understanding of physics. 

All you have to do is ask me for help and I will give you the derivation.

I understand it perfectly well.  You are the one that needs to get a better understanding of physics. 

All you have to do is ask me for help and I will give you the derivation.

Let me see, you jump out of an airplane and the air accelerating up from the surface of the earth is accelerating at a rate of 9.8m/s/s, hits your body causing a resistive force that causes you to accelerate up, so at what point does your velocity stop increasing?

Relative to the Earth?  When your upwards acceleration equals the acceleration of the Earth.

But, I've said this already.

if you are talking about the FE model there is no force other than the acceleration caused by the air resistance in the RE model the downward force is in the gravitational acceleration and the objects mass

Gravitation is not a force. It does not cause one to accelerate.

Gravitation is not a force. It does not cause one to accelerate.

Gravitation most certainly causes objects to accelerate. 

just bringing this to the top.

Quote from: Jack. on August 19, 2008, 08:40:00 AM

Quote from: sokarul on August 19, 2008, 08:15:37 AM

Yes I do.  Locally straight paths through curved spacetime. 

You haven't completely answered my question.

I did.  You haven’t answered my attacks. 

Quote

Are you trying to argue that GR says gravitation causes downward acceleration?

It causes acceleration which can be downwards. 

Quote

He is always following a geodesic in spacetime, with the Earth acting as a mechanical resistance countering that. Thus, he is always in free fall. There is an upward force in the dude's chair.

He is not falling, nor is he free of external forces.  It is impossible for him to be in free fall. 

Quote from: sokarul on August 19, 2008, 08:15:37 AM

Please explain how a guy sitting in a chair on earth is the same thing as a astronaut feeling weightless in orbit.   

Quote

There is an upward force in the dude's chair

Astronauts are free of forces.  Not even close to the same thing. 

Scroll up.

Quote from: sokarul on August 19, 2008, 11:46:12 AM

I did.  You haven’t answered my attacks. 

Really?

Quote

Do you know what "motion along geodesic" is?

Quote from: sokarul on August 19, 2008, 11:46:12 AM

He is not falling, nor is he free of external forces.  It is impossible for him to be in free fall. 

He is moving along geodesics (free fall), but the mechanical resistance of the Earth (or his chair) disallows that. Is this really that hard for you to understand?

Quote from: sokarul on August 19, 2008, 11:46:12 AM

Astronauts are free of forces.  Not even close to the same thing. 

Obviously. However, we aren't, because there is an upward force under us due to mechanical resistance.

I'm always up for a good argument,

Then you've come to the wrong site. This is a satirical website.

Oh, you had already responded. 

Quote

Do you know what "motion along geodesic" is?

Yes. 

Quote

He is moving along geodesics (free fall), but the mechanical resistance of the Earth (or his chair) disallows that. Is this really that hard for you to understand?

I understand it, you cannot understand that he is no longer in free fall because he is in contact with the earth. 

Quote

Obviously. However, we aren't, because there is an upward force under us due to mechanical resistance.

Then stop saying we are in free fall while standing on the earth. 

Quote

Do you know what "motion along geodesic" is?

Yes. 

Then what is it?

I understand it, you cannot understand that he is no longer in free fall because he is in contact with the earth. 

So he is no longer following the geodesics in spacetime?

Then stop saying we are in free fall while standing on the earth. 

I never said they both are the same. Just because we're standing on Earth doesn't mean we're not in free-fall (or following the geodesics). If we aren't, we wouldn't be touching the ground nor there would be any upward force exerted underneath us.

Quote from: cbarnett97 on August 20, 2008, 12:18:40 AM

if you are talking about the FE model there is no force other than the acceleration caused by the air resistance in the RE model the downward force is in the gravitational acceleration and the objects mass

Gravitation is not a force. It does not cause one to accelerate.

If you want to very particular you can call it 'gravitational potential' if it makes you happy but for what we are analyizing here, we can consider it to be a force.

If you want to very particular you can call it 'gravitational potential' if it makes you happy but for what we are analyizing here, we can consider it to be a force.

I don't agree.

Relative to the Earth?  When your upwards acceleration equals the acceleration of the Earth.

But, I've said this already.

Made this using LaTex and I forgot to resize the page so sorry

Then what is it?

I don't know what answer you are looking for. 

So he is no longer following the geodesics in spacetime?

Yes.  He is still trying to, thus the physical acceleration he has. 

I never said they both are the same. Just because we're standing on Earth doesn't mean we're not in free-fall (or following the geodesics). If we aren't, we wouldn't be touching the ground nor there would be any upward force exerted underneath us.

Free fall and following the geodesics are not the same thing.  Free fall is defined as an object free of forces and accelerating only due to gravitation.

Your second equation isn't right.  Can you post your free body diagram?

I don't know what answer you are looking for. 

It's inertial motion; free-fall.

Yes.  He is still trying to, thus the physical acceleration he has. 

He still is falling, or following the geodesics, indirectly.

Free fall and following the geodesics are not the same thing.

They are equivalent. How can you deny that? Geodesic motion = Inertial motion. Free fall = Inertial motion. When you are free-falling, you are following the geodesics, the straightest lines possible. Since the lines are curved in space-time, inertially moving objects (free-falling) accelerate towards each other. That's why the curvature of space-time causes acceleration.

Free fall is defined as an object free of forces and accelerating only due to gravitation.

He still is falling, or following the geodesics, indirectly.

1 Gravitation keeps a person on the ground.
2 Gravitation is the curvature of spacetime.
3 The curvature of spacetime is composed of geodesics.
---
4 Therefore, for gravitation to keep a person on the ground, he/she must follow the geodesics in curved space-time. This also explains why objects undergoing inertial motion accelerate towards each other.

Cbarnett97, your equation basically says drag=ma which isn't right.  The numerical model you created would be the difference in acceleration due to drag.  So the correct model would be:

T1=9.8-0.115=9.685    V=9.685

T2=9.8-0.462=9.338    V=19.023

T3=9.8-1.039=8.761    V=27.784

Which would put you at 22.117m/s at 2.26s.   

Made this using LaTex and I forgot to resize the page so sorry

Your second equation is exactly the same as your first one except that you have an extra 2 in it. If, as I suspect, this discrepancy is error on your part, then you have simply shown that the two models predict exactly the same thing.

Quote from: sokarul on August 21, 2008, 07:51:38 AM

I don't know what answer you are looking for. 

It's inertial motion; free-fall.

One can follow geodesics while not being in free fall. 

Quote from: sokarul on August 21, 2008, 07:51:38 AM

Yes.  He is still trying to, thus the physical acceleration he has. 

He still is falling, or following the geodesics, indirectly.

Quote from: sokarul on August 21, 2008, 07:51:38 AM

Free fall and following the geodesics are not the same thing.

They are equivalent. How can you deny that? Geodesic motion = Inertial motion. Free fall = Inertial motion. When you are free-falling, you are following the geodesics, the straightest lines possible. Since the lines are curved in space-time, inertially moving objects (free-falling) accelerate towards each other. That's why the curvature of space-time causes acceleration.

Quote from: sokarul on August 21, 2008, 07:51:38 AM

Free fall is defined as an object free of forces and accelerating only due to gravitation.

Quote

He still is falling, or following the geodesics, indirectly.

1 Gravitation keeps a person on the ground.
2 Gravitation is the curvature of spacetime.
3 The curvature of spacetime is composed of geodesics.
---
4 Therefore, for gravitation to keep a person on the ground, he/she must follow the geodesics in curved space-time. This also explains why objects undergoing inertial motion accelerate towards each other.

Ok, so now you see why its wrong to say a guy sitting in a chair is in free fall.

One can follow geodesics while not being in free fall. 

Then show me the sources.

Ok, so now you see why its wrong to say a guy sitting in a chair is in free fall.

He still is falling, or following the geodesics, indirectly.

Quote from: TheEngineer on August 20, 2008, 12:29:05 AM

Relative to the Earth?  When your upwards acceleration equals the acceleration of the Earth.

But, I've said this already.

Made this using LaTex and I forgot to resize the page so sorry

Your 'FE' equation is wrong.  Since you let us all have a good laugh, I'll go ahead and post the derivation for you.

The drag force on a body in a fluid is given by
 
F = .5*C_d*v²*A*rho                                                       (1)

where C_d is the drag coefficient, v is the velocity of the object, A is the cross sectional area of the object and rho is the density of the fluid.

We know from Newton's Second Law of Motion that

F = m*a_o                                                                      (2)

where F is force, m is the mass of the object and a_o is the acceleration of the object.  Rearranging (2) gives us

a_o = F/m                                                                       (3)

Combining (3) and (1) gives

a_o = C_d*v²*A*rho/(2*m)                                                 (4)

Now, an object that has reached terminal velocity, v_t, has no relative acceleration to the Earth.  Applying this to the FE, that means that the object must have an upwards acceleration equal to that of the Earth's.  It follows then, that

a_e - a_o = 0                                                                   (5)

where a_e is the acceleration of the Earth and a_o is the acceleration of the object. 

Rearranging (5) gives

a_e = a_o                                                                        (6)

which, by examination, is correct for all objects whose height is not changing relative to the Earth (aircraft for example). 

Combining (6) and (4) leaves us with the equation

a_e = C_d*v_t²*A*rho/(2*m)                                              (7)

Performing simple algebra on (7) yields the equation

v_t = sqrt(2*a_e*m/(Cd*A*rho)                                          (8)

which can easily been seen to be the exact same equation as the one for the RE, with the exception that a_e refers to the acceleration of the Earth and a in the RE equation refers to the acceleration due to gravity.

Using your numbers, we see that the terminal velocity on the FE is 22.1426 m/s.



p.s.  Your RE equation is wrong.

Quote from: cbarnett97 on August 21, 2008, 05:28:59 AM

Quote from: TheEngineer on August 20, 2008, 12:29:05 AM

Relative to the Earth?  When your upwards acceleration equals the acceleration of the Earth.

But, I've said this already.

Made this using LaTex and I forgot to resize the page so sorry

Your 'FE' equation is wrong.  Since you let us all have a good laugh, I'll go ahead and post the derivation for you.

The drag force on a body in a fluid is given by
 
F = .5*C_d*v²*A*rho                                                       (1)

where C_d is the drag coefficient, v is the velocity of the object, A is the cross sectional area of the object and rho is the density of the fluid.

We know from Newton's Second Law of Motion that

F = m*a_o                                                                      (2)

where F is force, m is the mass of the object and a_o is the acceleration of the object.  Rearranging (2) gives us

a_o = F/m                                                                       (3)

Combining (3) and (1) gives

a_o = C_d*v²*A*rho/(2*m)                                                 (4)

Now, an object that has reached terminal velocity, v_t, has no relative acceleration to the Earth.  Applying this to the FE, that means that the object must have an upwards acceleration equal to that of the Earth's.  It follows then, that

a_e - a_o = 0                                                                   (5)

where a_e is the acceleration of the Earth and a_o is the acceleration of the object. 

Rearranging (5) gives

a_e = a_o                                                                        (6)

which, by examination, is correct for all objects whose height is not changing relative to the Earth (aircraft for example). 

Combining (6) and (4) leaves us with the equation

a_e = C_d*v_t²*A*rho/(2*m)                                              (7)

Performing simple algebra on (7) yields the equation

v_t = sqrt(2*a_e*m/(Cd*A*rho)                                          (8)

which can easily been seen to be the exact same equation as the one for the RE, with the exception that a_e refers to the acceleration of the Earth and a in the RE equation refers to the acceleration due to gravity.

Using your numbers, we see that the terminal velocity on the FE is 22.1426 m/s.



p.s.  Your RE equation is wrong.

Learn how to do a freebody diagram and get back to us

Quote from: sokarul on August 21, 2008, 09:09:20 AM

One can follow geodesics while not being in free fall. 

Then show me the sources.

See GR.  Also jump in the air.  Congrats you followed them without being in free fall. 

Quote

He still is falling, or following the geodesics, indirectly.

Still doesn't mean he is in free fall as he is still not free from external forces. 

Cbarnett97, your equation basically says drag=ma which isn't right.  The numerical model you created would be the difference in acceleration due to drag.  So the correct model would be:

T1=9.8-0.115=9.685    V=9.685

T2=9.8-0.462=9.338    V=19.023

T3=9.8-1.039=8.761    V=27.784

Which would put you at 22.117m/s at 2.26s.   

what is being accelerated in the FE model the person or the air?

Both.

Both.

and what is causing the person to be accelerated

The accelerating air for the same reason that air slows your acceleration normally, just in reverse.

Learn how to do a freebody diagram and get back to us

We have a perfectly derived equation and that is the best you can do?  Wow, you really do suck at this stuff.  I suggest you go back to school, learn some more high school physics, then try to prove me wrong.  Because your middle school knowledge of physics is not going to cut it.

Quote from: cbarnett97 on August 21, 2008, 01:12:37 PM

Learn how to do a freebody diagram and get back to us

We have a perfectly derived equation and that is the best you can do?  Wow, you really do suck at this stuff.  I suggest you go back to school, learn some more high school physics, then try to prove me wrong.  Because your middle school knowledge of physics is not going to cut it.

Your understanding of the FE model is sickening I suggest you learn how to read and then go ahead and show that it is perfectly ok to add items into your equation that do not exist for that system and how you can make a known magically become an unknown and then you can work on the ability to solve something based upon a model instead of trying to force it to fit reality