Looking for an intelligent argument. (Terminal Velocity)

It is the same.  Air is rushing past you at the same speed in RE and FE.  Air resistance will be the same, you will reach terminal velocity in the same amount of time as in RE.

RE 1. Jump out airplane. 2. Start to fall towards Earth at 9.8 m/s 2. 3. Air continues to accelerate past you, increasing air resistance.      4. Air resistance causes person to accelerate at 0 m/s2. 5. You reach terminal velocity.

FE 1. Jump out airplane. 2. Earth moves toward you at 9.8 m/s 2. 3. Air continue to accelerate past you, increasing air resistance. 4. Air resistance causes person to accelerate at 0 m/s2. 5. You reach terminal velocity.

There is absolutely no difference.

Even my little brother gets that (he's only 10).

Quote from: Trekky0623 on August 31, 2008, 09:31:04 PM

It is the same.  Air is rushing past you at the same speed in RE and FE.  Air resistance will be the same, you will reach terminal velocity in the same amount of time as in RE.

RE 1. Jump out airplane. 2. Start to fall towards Earth at 9.8 m/s 2. 3. Air continues to accelerate past you, increasing air resistance.      4. Air resistance causes person to accelerate at 0 m/s2. 5. You reach terminal velocity.

FE 1. Jump out airplane. 2. Earth moves toward you at 9.8 m/s 2. 3. Air continue to accelerate past you, increasing air resistance. 4. Air resistance causes person to accelerate at 0 m/s2. 5. You reach terminal velocity.

There is absolutely no difference.

Even my little brother gets that (he's only 10).

of course, if you do not understand the science behind it then it makes perfect sense

that is the mistake theengineer is making and everyone is following his lead, you can not relate it to the earth until you have reached your point of equalibrium.

It's equilibrium, kid. 

Quote from: cbarnett97 on August 31, 2008, 03:20:53 PM

the whole idea of doing a free body diagram is to look at the forces acting on the body.

And like I said already, there is no balancing force.  Therefore there is a constant acceleration. 

I believe this is too complicated for you to follow.  I thought my derivation was simple enough for you.  Apparently, I gave you too much credit.  We are only interested in the velocity at a certain acceleration.  Is that simple enough for you?

Quote from: cbarnett97 on August 31, 2008, 09:36:56 PM

that is the mistake theengineer is making and everyone is following his lead, you can not relate it to the earth until you have reached your point of equalibrium.

It's equilibrium, kid. 

Quote

Quote from: cbarnett97 on August 31, 2008, 03:20:53 PM

the whole idea of doing a free body diagram is to look at the forces acting on the body.

And like I said already, there is no balancing force.  Therefore there is a constant acceleration. 

I believe this is too complicated for you to follow.  I thought my derivation was simple enough for you.  Apparently, I gave you too much credit.  We are only interested in the velocity at a certain acceleration.  Is that simple enough for you?

so using the FE model what would an accelerometer show at t=2

Why is it that every topic I enter, FE'ers never give a good debate?  I'm beginning to think the whole website is a joke.

It is a joke. Some think the earth is held up by turtles and elephants.
It's like the LBC.

Quote from: kainedamo on August 15, 2008, 03:28:46 PM

Why is it that every topic I enter, FE'ers never give a good debate?  I'm beginning to think the whole website is a joke.

It is a joke. Some think the earth is held up by turtles and elephants.
It's like the LBC.

the turtles and elephants part is a joke.
the BoP is on you guys. youre the ones that dont believe.

of course, if you do not understand the science behind it then it makes perfect sense

That's what you're doing in this thread right now.

since you understand the model so well go ahead and take a shot at this

Quote from: TheEngineer on August 31, 2008, 10:00:12 PM

Quote from: cbarnett97 on August 31, 2008, 09:36:56 PM

that is the mistake theengineer is making and everyone is following his lead, you can not relate it to the earth until you have reached your point of equalibrium.

It's equilibrium, kid. 

Quote

Quote from: cbarnett97 on August 31, 2008, 03:20:53 PM

the whole idea of doing a free body diagram is to look at the forces acting on the body.

And like I said already, there is no balancing force.  Therefore there is a constant acceleration. 

I believe this is too complicated for you to follow.  I thought my derivation was simple enough for you.  Apparently, I gave you too much credit.  We are only interested in the velocity at a certain acceleration.  Is that simple enough for you?

so using the FE model what would an accelerometer show at t=2

How can you deny this? It's just some freshman physics...

It is the same.  Air is rushing past you at the same speed in RE and FE.  Air resistance will be the same, you will reach terminal velocity in the same amount of time as in RE.

RE 1. Jump out airplane. 2. Start to fall towards Earth at 9.8 m/s 2. 3. Air continues to accelerate past you, increasing air resistance.      4. Air resistance causes person to accelerate at 0 m/s2. 5. You reach terminal velocity.

FE 1. Jump out airplane. 2. Earth moves toward you at 9.8 m/s 2. 3. Air continue to accelerate past you, increasing air resistance. 4. Air resistance causes person to accelerate at 0 m/s2. 5. You reach terminal velocity.

There is absolutely no difference.

How can you deny this? It's just some freshman physics...

Quote from: Trekky0623 on August 31, 2008, 09:31:04 PM

It is the same.  Air is rushing past you at the same speed in RE and FE.  Air resistance will be the same, you will reach terminal velocity in the same amount of time as in RE.

RE 1. Jump out airplane. 2. Start to fall towards Earth at 9.8 m/s 2. 3. Air continues to accelerate past you, increasing air resistance.      4. Air resistance causes person to accelerate at 0 m/s2. 5. You reach terminal velocity.

FE 1. Jump out airplane. 2. Earth moves toward you at 9.8 m/s 2. 3. Air continue to accelerate past you, increasing air resistance. 4. Air resistance causes person to accelerate at 0 m/s2. 5. You reach terminal velocity.

There is absolutely no difference.

In the FE model the acceleration of the earth is not in the system so it can not be accounted for. after you obtain the behavior of the object you can then relate that to the surface of the earth, so how about you go ahead and show me the accleration of the object a t=2 using the FE model

so using the FE model what would an accelerometer show at t=2

What is an accelerometer and how does it work?

In the FE model the acceleration of the earth is not in the system so it can not be accounted for. after you obtain the behavior of the object you can then relate that to the surface of the earth, so how about you go ahead and show me the accleration of the object a t=2 using the FE model

Why are we solving for the acceleration?

Quote from: cbarnett97 on August 31, 2008, 10:03:42 PM

so using the FE model what would an accelerometer show at t=2

What is an accelerometer and how does it work?

basically it measures acceleration. it is big in safety tests to test the amount of force delivered to objects.

Quote from: cbarnett97 on September 01, 2008, 01:35:06 AM

In the FE model the acceleration of the earth is not in the system so it can not be accounted for. after you obtain the behavior of the object you can then relate that to the surface of the earth, so how about you go ahead and show me the accleration of the object a t=2 using the FE model

Why are we solving for the acceleration?

that is what is changing in the FE model, if it will make you happy you can calculate the velocity of the object at t=2, I just thought i would save you a step since you would need to calculate the acceleration first.

Here we go again...

Here we go again...

the reason we are going again is because theengineer and his little minions look at the end behavior and then assume that everything from start to finish is exactly the same in both models, like I said before just because 2 cars can both go 60 mph does not mean that they get to that 60mph the same way

Sorry I didn't have time to go over this "argument", but when did they claim that?

Quote from: Fletch on September 01, 2008, 01:41:39 AM

Quote from: cbarnett97 on August 31, 2008, 10:03:42 PM

so using the FE model what would an accelerometer show at t=2

What is an accelerometer and how does it work?

basically it measures acceleration. it is big in safety tests to test the amount of force delivered to objects.

Beyond basically though, how does it measure acceleration? As you jump out of a plane, what is it measuring? Sorry, I mean how is it measuring it?

Sorry I didn't have time to go over this "argument", but when did they claim that?

by relating the entire acceleration to the surface of the earth because the end result of the object should be 9.81m/s/s.

Quote from: cbarnett97 on September 01, 2008, 01:43:23 AM

Quote from: Fletch on September 01, 2008, 01:41:39 AM

Quote from: cbarnett97 on August 31, 2008, 10:03:42 PM

so using the FE model what would an accelerometer show at t=2

What is an accelerometer and how does it work?

basically it measures acceleration. it is big in safety tests to test the amount of force delivered to objects.

Beyond basically though, how does it measure acceleration? As you jump out of a plane, what is it measuring? Sorry, I mean how is it measuring it?

Someone correct me if I am wrong, but if I remember correctly it basically measures a force from a known mass then gets the acceleration from that. F=mass x acceleration

Quote from: e.Jack on September 01, 2008, 01:51:40 AM

Sorry I didn't have time to go over this "argument", but when did they claim that?

by relating the entire acceleration to the surface of the earth because the end result of the object should be 9.81m/s/s.

But they say there are no balancing forces. There is only a constant upwards acceleration relative to the Earth's.

Someone correct me if I am wrong, but if I remember correctly it basically measures a force from a known mass then gets the acceleration from that. F=mass x acceleration

So in RE, when you jump from your plane, what/how is it measuring?

An accelerometer does not measure the '1g' of the Earth until you are at terminal velocity in either the RE or FE model. By definition free fall (without air resistance) is a relative state of rest (objects following geodesics), so if it could measure 'absolute acceleration' then you would have a means of figuring out the 'preferred rest frame' of the Universe, which is forbidden in relativity.

To clarify, an accelerometer would read (in the vertical axis, with '+' meaning 'upwards'):

1) stationary on the runway
 RE : +1g (9.81ms^-2) contact acceleration
 FE : +1a_UA (9.81ms^-2) contact acceleration

2) climbing to drop altitude
 RE : +1g + (vertical acceleration of aircraft)
 FE : +1a_UA + (vertical acceleration of aircraft)

3) level at drop alitutude
 RE : +1g - (small correction for altitude (g drops as 1/r² from surface of Earth))
 FE : +1a_UA - (small correction for altitude (source depends on your 'flavour' of FE))

4) the instant that Tom Bishop jumps out horizontally from the door
 RE : zero
 FE : zero

5) before reaching terminal velocity
 RE : zero + (air resistance as fall towards Earth at 1g acceleration [acceleration as measured from the ground])
 FE : zero + (air resistance as fall towards Earth at 1a_UA acceleration [acceleration as measured from the ground])

6) terminal velocity
 RE : +1g
 FE : +1a_UA

As you can see, the two are identical at all points. Neither accelerates faster than the other and neither 'feels' any different at any point (so long as you have a reasonable physical explanation for g dropping off with altitude, which FE provides a few alternative theories for). If I'm wrong at any point here, feel free to explain why.

An accelerometer does not measure the '1g' of the Earth until you are at terminal velocity in either the RE or FE model. By definition free fall (without air resistance) is a relative state of rest (objects following geodesics), so if it could measure 'absolute acceleration' then you would have a means of figuring out the 'preferred rest frame' of the Universe, which is forbidden in relativity.

To clarify, an accelerometer would read (in the vertical axis, with '+' meaning 'upwards'):

1) stationary on the runway
 RE : +1g (9.81ms^-2) contact acceleration
 FE : +1a_UA (9.81ms^-2) contact acceleration

2) climbing to drop altitude
 RE : +1g + (vertical acceleration of aircraft)
 FE : +1a_UA + (vertical acceleration of aircraft)

3) level at drop alitutude
 RE : +1g - (small correction for altitude (g drops as 1/r² from surface of Earth))
 FE : +1a_UA - (small correction for altitude (source depends on your 'flavour' of FE))

4) the instant that Tom Bishop jumps out horizontally from the door
 RE : zero
 FE : zero

5) before reaching terminal velocity
 RE : zero + (air resistance as fall towards Earth at 1g acceleration [acceleration as measured from the ground]) FE : zero + (air resistance as fall towards Earth at 1a_UA acceleration [acceleration as measured from the ground])

6) terminal velocity
 RE : +1g
 FE : +1a_UA

As you can see, the two are identical at all points. Neither accelerates faster than the other and neither 'feels' any different at any point (so long as you have a reasonable physical explanation for g dropping off with altitude, which FE provides a few alternative theories for). If I'm wrong at any point here, feel free to explain why.

close but the bolded parts are not allowed as they are not in the system also when you jump out of the airplane the acceleration in the RE model will still be 9.81m/s/s only in the FE will it be zero.

close but the bolded parts are not allowed as they are not in the system also when you jump out of the airplane the acceleration in the RE model will still be 9.81m/s/s only in the FE will it be zero.

Compared to what? That's why I'm trying to find out how an acceleromator works? What/how is it measuring?

Quote from: cbarnett97 on September 01, 2008, 03:49:48 AM

close but the bolded parts are not allowed as they are not in the system also when you jump out of the airplane the acceleration in the RE model will still be 9.81m/s/s only in the FE will it be zero.

Compared to what? That's why I'm trying to find out how an acceleromator works? What/how is it measuring?

an accelerometer measure acceleration relative to itsself.
this is how the majority of them are set up. The have a cantilever beam with a proof mass (also known as seismic mass) and some type of deflection sensing circuitry. Under the influence of gravity or acceleration the proof mass deflects from its neutral position. The deflection is measured in an analog or digital manner. Another type of MEMS-based accelerometer contains a small heater at the bottom of a very small dome, which heats the air inside the dome to cause it to rise. A thermocouple on the dome determines where the heated air reaches the dome and the deflection off the center is a measure of the acceleration applied to the sensor.

cbarnett - you can remove the parts in bold and my statement remains valid.  You have ignored the whole point of my post, but I will frame it in the context of yours in the interests of civil discussion.

You are correct that accelerometers are essentially cantilevers or springs (either macroscopic of MEMS, that part is irrelevant to everything other than their accuracy and size). Are you trying to say that in vacuum free fall an accelerometer can measure gravity? This is completely untrue - as I said if this were possible then an accelerometer would be all you would need to determine an absolute Universal rest frame, which is forbidden by relativity.  Even if you allow such a frame to exist, an accelerometer doesn't have some magic mass bound to that frame to measure against.

An accelerometer can not measure gravity in free fall. It can measure the acceleration caused by drag, but in vacuum free fall it will show exactly zero acceleration, even if you are in orbit.

If you don't believe me, then wiki also supports this line of reasoning:

Conversely, the device's output will be zero during free fall, where the acceleration exactly follows gravity. This includes use in an earth orbiting spaceship, but not a (non-free) fall with air resistance, where drag forces reduce the acceleration until terminal velocity is reached, at which point the device would once again indicate the 1 g vertical offset.

an accelerometer measure acceleration relative to itsself.
this is how the majority of them are set up. The have a cantilever beam with a proof mass (also known as seismic mass) and some type of deflection sensing circuitry. Under the influence of gravity or acceleration the proof mass deflects from its neutral position. The deflection is measured in an analog or digital manner.

Wow, is there no end to man's ingenuity.

In that case, in FET all the worlds accelerometers are set to read an upwards acceleration of 9.8ms/s as Zero acceleration. Therefore the accelerometer in the airplane, assuming the plane is at a constant height above sea level, is accelerating up at 9.8ms/s with the plane/with the atmosphere/with the earth, and therefore reads 0.

Then you leap out of the plane with it and you/it stops accelerating up, and instead continue to travel up at the velocity the plane/the atmosphere/the earth was traveling at the moment you left the plane. The accelometer would therefore register the change of acceleration as (-) 9.8ms/s because it is no longer accelerating in the "up" direction. The plane/atmosphere/earth continue to accelerate "up" at 9.8ms/s and the accelerometer continues to read a downward acceleration of 9.8ms/s

Then you can take into account the wind resistance and terminal velocities, etc, but the fact is it reads the same in both RET and FET.

In that case, in FET all the worlds accelerometers are set to read an upwards acceleration of 9.8ms/s as Zero acceleration. Therefore the accelerometer in the airplane, assuming the plane is at a constant height above sea level, is accelerating up at 9.8ms/s with the plane/with the atmosphere/with the earth, and therefore reads 0.

Then you leap out of the plane with it and you/it stops accelerating up, and instead continue to travel up at the velocity the plane/the atmosphere/the earth was traveling at the moment you left the plane. The accelometer would therefore register the change of acceleration as (-) 9.8ms/s because it is no longer accelerating in the "up" direction. The plane/atmosphere/earth continue to accelerate "up" at 9.8ms/s and the accelerometer continues to read a downward acceleration of 9.8ms/s

The accelerometer will read as I have described in my previous post. It will change from reading the acceleration due to gravitation/UA in the plane (flying at constant altitude) to reading zero when you leave the plane. It then registers a gradual increase until, at terminal velocity, it measures the same as when you were on the ground/in the plane.

The key is to remember that the accelerometer cannot 'see' the ground, it only has internal workings to go on.  This explains why it can't sense gravitation in free-fall, only the effects of drag (which, at terminal velocity, are the same as the contact acceleration on the ground).

Then you can take into account the wind resistance and terminal velocities, etc, but the fact is it reads the same in both RET and FET.

Yep, spot on (at all times).

The accelerometer will read as I have described in my previous post. It will change from reading the acceleration due to gravitation/UA in the plane (flying at constant altitude) to reading zero when you leave the plane. It then registers a gradual increase until, at terminal velocity, it measures the same as when you were on the ground/in the plane.

The key is to remember that the accelerometer cannot 'see' the ground, it only has internal workings to go on.  This explains why it can't sense gravitation in free-fall, only the effects of drag (which, at terminal velocity, are the same as the contact acceleration on the ground).

I've obviously misinterpreted barnets post. If we're travelling in a plane at a constant speed at a constant height above Sea Level, what is the reading on the acclerometer? And what is it measuring?