Split Thread The validity of classical physics (split from: DWFTTW)

[Dan O.]

If the force from a parachute is linear with velocity, then that is simply;
Power (available) = force* distance/time = force * velocity.

Then how about this, Dan?

I'm afraid I can't accept that one. It's a conditional with a false condition so the statement overall is true.

 

[Dan O.]

And this one, Dan?

I submitted an extended entry. The editor had to trim it a bit but I think it's an improvement.

• "Motion relative to the supermarket belt is also relative to the ground. Both directions yield the same KE, if viewed from belt or ground." #3053

ETA: I see that humber is making a nomination to remove some of the entries in the Where humber is wrong list. If those are seconded they can be removed assuming there is no call for discussion.

 

[humber]

Ok, since you want to talk about an "Absolute Accelerometer" I will need more background information. Could you assist me please?
I suppose that absolute acceleration is the rate of change of absolute velocity wrt time. Is that correct?

For linear motion, it is the change in velocity w.r.t time, that is the result of an applied force. NB: The large volumes written upon this topic suggest that may not be a complete description.

And absolute velocity is the rate of change of absolute position wrt time. Correct?

That motion is implied, but the 'absolute' is unnecessary.

Could you tell how you define absolute position?

My PC monitor is absolutely in front of me, Dude.

This may help me understand. Is it all about the start of the universe?

If that helps you understand, then it would surprise me.

Could you tell me where it started.

In a Galaxy, far, far away, so I am told.
Perhaps Steven Weinberg's "The First Three Minutes" is worth thumbing through.

Is it getting bigger,

Perhaps, but I think it's quite big enough. Don't you?

will it continue to grow forever?

I think forever is overly ambitious.

What does time mean anyway?

What does 'one meter away' mean? Can you tell me that?
ETA: Time is what stops everything from happening at once.

Now you are starting to get somewhere Mr Humber.

Puffs on pipe...Mmmm.

 

[RossFW]

See Newton

.....EXCEPT the bit about all frames of reference being equal!!

....ETA AND except the bit that a body with no net force applied does not accelerate (You are suggesting motion without force!!) and it's corollary, an object WITH a force applied (Say a balloon or kite not at windspeed) DOES accelerate.

Maybe you meant WAYNE Newton!

MORE Gold!!

 

[RossFW]

Google "absolute accelerometers"

2) 0 g. No, that is wrong, and contradicts your own idea. The velocity of the elevator may not be known, but it is accelerating due to gravity. As it in not being slowed, that is 1g if close to the surface. ETA It The force is there if the accelerometer says so or not. There is a difference between the gravitational force, and acceleration due to that force.

Nope. More proof you just don't get the whole "Thing are relative" stuff.

Being in freefall in a gravity field is identical to being in zero 'G' in deep space. The accelerometers velocity wrt everything around it is zero. All it's internal components are in uniform acceleration, so it cannot detect any change in velocity.

YES it is accelerating wrt the Earths surface, but when will it start to dawn on you that something that isn't ON the earths surface (Cart, Kite, Aircraft, Balloon) has no direct relationship with the Earths surface?

Exactly the same applies in a spaceship in orbit.

Without further information, a "Relative" accelerometer (a "G" meter in My patch!) you could not determine whether you were in a spaceship in orbit, a (Non spinning) spaceship in deep space, or a box in freefall.

You've been told this countless times, but maybe your response will get me on dan's list without having to troll through a million posts!!

 

[humber]

Nope. More proof you just don't get the whole "Thing are relative" stuff

Being in freefall in a gravity field is identical to being in zero 'G' in deep space.

'This is your Captain speaking. Don't be alarmed folks, plummeting to Earth is just like being in the zero gravity of space. Oh...that's fatal too...bummer.'

So they are the same after all.

You are in free-fall because of gravity. If you could suddenly remove that, and all other influences including the air, then you would continue at the same velocity, but not continue to accelerate. If the air were introduced, then you would slow as the body's KE expends itself against the work of friction. In practice, on this planet, those actions are concurrent under gravity.

The accelerometers velocity wrt everything around it is zero. All it's internal components are in uniform acceleration, so it cannot detect any change in velocity.

No. Actually not. Even withing the gravitational field close the the Earth, that gradient can be measured. In fact, it can stress a simple rod, and the resultant strain detected.

YES it is accelerating wrt the Earths surface, but when will it start to dawn on you that something that isn't ON the earths surface (Cart, Kite, Aircraft, Balloon) has no direct relationship with the Earths surface?

I imagine that moment will come when I disavow my allegiance to geostationary orbit. Balloons move relative to the ground, unless they in the state we Groundians call "stationary".

Exactly the same applies in a spaceship in orbit.

Yes.

Without further information, a "Relative" accelerometer (a "G" meter in My patch!) you could not determine whether you were in a spaceship in orbit, a (Non spinning) spaceship in deep space, or a box in freefall.

Einstein in a lift, again. Don't ever go to a tall building with that guy.
What is your point RossFW? You have to resurrect absolutism, in order to deny it, and now there is the new caveat (non spinning).

There is nothing to be gained from trying to make the hypothetical real.
Take a real car driving on a real road at 50kph. You say that can be modeled by putting the car on a belt going backwards at that same speed.
No.
Why should the belt turn the wheels? From your own logic, the car and its driver 'can't tell' the road is moving, so what expectation can there be that the belt (road) would turn the wheels?

You've been told this countless times, but maybe your response will get me on dan's list without having to troll through a million posts!!

That list is by invitation only.

 

[mender]

No. The force is approximately linearly proportional to the relative velocity of chute and wind.

Then how about this one, Dan? Humber makes an unconditional statement this time in response to and denial of my correct statement.

 

[spork]

Motion is denied.

JB

Also specificity, definition, and consistency are denied. That's why it's almost completely pointless to ask humber to define things, be specific, or review things he's posted in the past.

I say almost because there is sometimes entertainment to be had.

 

[RossFW]

AND there it is!

I imagine that moment will come when I disavow my allegiance to geostationary orbit. Balloons move relative to the ground, unless they in the state we Groundians call "stationary".

[post=]#3066[/post]

So nominated Dan!

Dag nab it! Can't the post thingy to work. Can someone help me?

 

[RossFW]

'This is your Captain speaking. Don't be alarmed folks, plummeting to Earth is just like being in the zero gravity of space. Oh...that's fatal too...bummer.'

It most certainly is. These guys let passengers experience weightlessness by putting the aircraft into a vertical acceleration equal to the acceleration due to gravity. Guess what their 'G' meter is reading?


http://au.youtube.com/watch?v=NkXrpbOEWC4&feature=related

 

[Dan O.]

AND there it is!

• "Balloons move relative to the ground, unless they in the state we Groundians call "stationary"" #3066

So nominated Dan!

Since it's not an incorrect statement but does illustrate where humber has taken root in his earth-centric view, I'll put it with Some more of humber's wrong doings.

Dag nab it! Can't the post thingy to work. Can someone help me?

There are 2 post numbers. The one you see (#3066) and the hidden unique post number (p=4393331). The first one can change if a moderator moves some posts around in the threads so you need the second one if you want to create a static pointer to a post. If you quote a post, the hidden number shows up in the url that gets inserted. You can also hover you mouse over the number in the top right of a post and see a URL in the status line with the hidden post number.

You can just use the "QUOTE" button on the post as others have done and I'll pick up the numbers when I edit it into the list.

 

[Dan O.]

Then how about this one, Dan? Humber makes an unconditional statement this time in response to and denial of my correct statement.

Seconded.

I was getting some strange results trying to verify what Raleigh's equation was until I took Google's suggestion and looked for Rayleigh's equation.

The continuing list of Where humber is wrong

• "The force is approximately linearly proportional to the relative velocity of chute and wind." #2951
  

 

[Michael C]

1. What value does an accelerometer show in an elevator, stationary at the surface of the earth?

2. What value does an accelerometer show in an elevator in free fall at the surface of the earth? The elevator is falling in a vacuum: its fall is not being slowed down by any mechanical friction or air drag.

3. What value does an accelerometer show in an unpowered spaceship orbiting the earth?

4. What value does an accelerometer show in an unpowered spaceship floating in outer space, far away from the gravitational influences of any stars?

By "accelerometer" I meant what is commonly known as an "accelerometer", no more, no less. I was not referring to something that measures change of position relative to another object. I was not referring to a hypothetical "absolute accelerometer" such as the one described in mender's link (http://www.wbabin.net/yuri/keilman5.pdf), which, if it could work as the author of the article suggests, would falsify the theory of relativity.

1) 1 g.
2) 0 g.
3) 0 g.
4) 0 g.

Mender's replies are, of course, correct: in free fall with no air drag you will experience no acceleration forces, regardless of your distance from the earth.

Bonus question: in question 1, what is the direction of the 1 g measured?

 

[John Freestone]

Mender's replies are, of course, correct: in free fall with no air drag you will experience no acceleration forces, regardless of your distance from the earth.

Wouldn't you experience gravity, and the acceleration due to gravity, about 9.8 m/s/s? I thought so, and seem to be finding some sources to support that. They say that your accelerometer (the generally used kind) would read zero, but only because it is calibrated to ignore 1g, i.e. to read 1 when you're not accelerating w.r.t. the Earth. How could you experience no acceleration forces, yet plummet towards the ground? If there were a shaft through the earth, you'd slow down to a stop and come back again, so how can that not be a body experiencing acceleration?

The questions are a bit "tricky" in that sense, it seems to me. Someone in orbit (which is what you are in freefall in a lift, BTW, only the orbit is part of a zero-width elipse), is accelerating, I thought, since their velocity is constantly changing its direction and perhaps magnitude. Why? Due to gravity. Have I got it wrong?

I must say, I'm not quite sure where that leaves someone in outer space where there is zero gravity: presumably if they used a normal ground-based accelerometer out of an aircraft, it would be reading 1g, but they are again not accelerating (without thrusters). The accelerometer would adjust for earth gravity, and there isn't any.

Bonus question: in question 1, what is the direction of the 1 g measured?

Normally, don't they read + 1 g? In freefall they read 0 g, and pulling up at 9.8 m/s/s they'd measure 2 g.

Even so, that acceleration is relative to something, as far as I can see, and here I'm thinking it's the Earth.

The Earth is rotating, and at the equator the acceleration of a body on it due to that rotational motion is about 0.03 m/s/s. Thanks to that and the longer distance to the centre, you weigh about 0.5 % less.

g at the poles is about 9.78, and at the equator, about 9.83 m/s/s, but relative to the ground, you don't get that acceleration of g until someone takes it away from under you, no?

 

[sol invictus]

Even so, that acceleration is relative to something, as far as I can see, and here I'm thinking it's the Earth.

Acceleration is not relative.

 

[humber]

a

Then how about this one, Dan? Humber makes an unconditional statement this time in response to and denial of my correct statement.

To a first approximation, and over most of its range, the force generated by a parachute is proportional to the difference between its velocity and that of the wind. Weather balloons certainly behave even more like that, because of their closed shape. That is not denial, Mender, but refutation.

As for your other example or a turbine, they are different, behaving in accordance with fan laws. (Also, they are not entirely scalable)

Equation 3, I think. (There are other approximations.)
http://www.cee1.org/ind/mot-rep/mot-rep-fanlaws.pdfi]k

 

[Marcus]

I haven't checked in on this thread for a while, and I find that two completely classic humberisms have been added(or more beyond page 60 where I'm at now)

Air Cavitation

Negative Drag

Thanks, Humber

 

[Michael C]

Wouldn't you experience gravity, and the acceleration due to gravity, about 9.8 m/s/s? I thought so, and seem to be finding some sources to support that. They say that your accelerometer (the generally used kind) would read zero, but only because it is calibrated to ignore 1g, i.e. to read 1 when you're not accelerating w.r.t. the Earth. How could you experience no acceleration forces, yet plummet towards the ground? If there were a shaft through the earth, you'd slow down to a stop and come back again, so how can that not be a body experiencing acceleration?

An accelerometer will read 1g vertically upwards when stationary at the earth's surface. This is not a calibration issue: it's the way the thing works. Have a look at this instruction booklet for an accelerometer, in particular at the "Frequent Questions" section. Or the Wikipedia article. Look also at this page from Einstein-Online, which gives a good explanation of the equivalence between elevator in free fall and spaceship without power.

The question of and elevator falling down a tunnel through the earth is an interesting one. Assuming that the tunnel has no air, so that the elevator is falling in a vacuum, the elevator will indeed oscillate indefinitely back and forth along the tunnel. Although the gravitational acceleration will be constantly changing (it'll be zero at the centre of the earth), the "free fall" condition still applies. The accelerometer will always read zero, and a person inside the elevator will always be in a state of weightlessness, just like the people in the video of a zero-g flight.

 

[humber]

By "accelerometer" I meant what is commonly known as an "accelerometer", no more, no less. I was not referring to something that measures change of position relative to another object. I was not referring to a hypothetical "absolute accelerometer" such as the one described in mender's link (http://www.wbabin.net/yuri/keilman5.pdf), which, if it could work as the author of the article suggests, would falsify the theory of relativity.

So often punctillious, but now it's "you know what I mean"
I did not sy Mender's post was what I had in mind. That is a possible class of device, but there is another class that can be used to deny the claim that it falsifies Relativity. (And what makes you so sure that is not possible? )

Another: http://www.iop.org/EJ/abstract/0049-1748/9/3/A18

Anyway, I answered all of the other questions on the basis of the accelerometer you have in mind.


Not the point I was trying to make. There are lots of opinions regarding acceleration.
http://www.physicsforums.com/showthread.php?t=59283
http://van.physics.uiuc.edu/qa/listing.php?id=1368

This is more useful;
http://www.physlink.com/education/askexperts/ae118.cfm

Humberverse: That the Suns rises, telling you that you are being accelerated.

Mender's replies are, of course, correct: in free fall with no air drag you will experience no acceleration forces, regardless of your distance from the earth.

Absurdity. Satellites immediately contradict you.

(1) d = vt + 1/2at^2

(2) Acceleration due to gravity;

g = (-mG/r^2)r

m is the mass of the object,
r is the distance from center of the objects or position
ris the unit length vector from center or position.
G is the gravitational constant of the universe.

Bonus question: in question 1, what is the direction of the 1 g measured?

Answered. I will let you know when I need a quiz, Michael_C.

 

[humber]

I haven't checked in on this thread for a while, and I find that two completely classic humberisms have been added(or more beyond page 60 where I'm at now)

Air Cavitation

Negative Drag

Thanks, Humber

Recursive Prophet asked that also. I will get back to it.