Things you always wanted to know the answer to [Vol. 3]

[deeen]

Einion Yrth said:

It's basic relativity, principle of equivalence stuff; if you are in an elevator, in a gravity field, with no windows. How do you tell if the elevator is moving or not, unless it accelerates?

You can't; (Mike McCulloch's MiHsC theory notwithstanding, since it would only represent a minor correction anyway.)

Same effort is involved in climbing any set of stairs, unless they are undergoing acceleration, (note movement at a constant velocity is not acceleration, for the physically challenged.)

Easy, check your weight (not your mass)!
Example... if the elevator drops at a staedy velocity of 11/metres per second, do you think the human inside could detect the movement?

[Einion Yrth]

deeen said:

Einion Yrth said:

All inertial frames of reference are equivalent; this really isn't up for discussion, at least not without some serious mathematical backup. An escalator, or elevator, or car, bus, aeroplane, swallow (european or african) that is not undergoing acceleration, is in an inertial frame. The equations by which we can predict motion, work, and energy (potential and kinetic) remain the same in any and all inertial frames, this is not news dammit.

Oh, please yourselves.

Agreed, for horizontal straight line travel. But a vwertical frame of referene (elevator) is affected by gravity. Example... if the elevator drops at a staedy velocity of 11/metres per second, do you think the human inside could detect the movement?

No.Assuming 1 standard g (9.8 ms^2) a constant velocity of 11 ms^1 would become indiscernable in just over a second (assuming we start from a non existent rest frame of 0 ms^1), like the slightly floaty feeling we have briefly as an express elevator begins its descent, thereafter - as in an express elevator (until it slows to its stop) everything would seem utterly and completely normal (as indeed it does, in an express elevator).

Edited by Einion Yrth on Saturday 30th April 21:02

[deeen]

singlecoil said:

cut...him at the same point?

So, let's see if we can find some areas of agreement as we jointly seek to establish the truth of this matter. First thing I hope we can agree on is that the heavier part of the person A's (person A is the one keeping station on the down escalator) body stays relatively still, and neither gains nor loses height. What say you (on that single point)?

Agreed.

Now imagine A is in free-fall.

What would be required to keep him at the same point?

[Einion Yrth]

deeen said:

Einion Yrth said:

deeen said:

Einion Yrth said:

All inertial frames of reference are equivalent; this really isn't up for discussion, at least not without some serious mathematical backup. An escalator, or elevator, or car, bus, aeroplane, swallow (european or african) that is not undergoing acceleration, is in an inertial frame. The equations by which we can predict motion, work, and energy (potential and kinetic) remain the same in any and all inertial frames, this is not news dammit.

Oh, please yourselves.

Agreed, for horizontal straight line travel. But a vwertical frame of referene (elevator) is affected by gravity. Example... if the elevator drops at a staedy velocity of 11/metres per second, do you think the human inside could detect the movement?

They'd not weigh much ( sorry I condidered doing the numbers, but I can't be arsed, so "not much" will do) and what looks like the ceiling would now be the floor, but if this velocity continued unaccelerated, no, he or she would not be able to detect any movement.

I think the fact that the ceiling had become the floor might alert said human to the fact that the lift was moving....

Serious answer, he would detect the fact he was moving by the change in his weight, not by the motion.

I deleted that, 'cause it's bks. I hadn't thought the problem through, (actually I am guilty in this post of the same sort of magical thinking that is plagueing the whole question; I am profoundly ashamed). See up for the actual answer.

[deeen]

Einion Yrth said:

deeen said:

Einion Yrth said:

All inertial frames of reference are equivalent; this really isn't up for discussion, at least not without some serious mathematical backup. An escalator, or elevator, or car, bus, aeroplane, swallow (european or african) that is not undergoing acceleration, is in an inertial frame. The equations by which we can predict motion, work, and energy (potential and kinetic) remain the same in any and all inertial frames, this is not news dammit.

Oh, please yourselves.

Agreed, for horizontal straight line travel. But a vwertical frame of referene (elevator) is affected by gravity. Example... if the elevator drops at a staedy velocity of 11/metres per second, do you think the human inside could detect the movement?

No.Assuming 1 standard g (9.8 ms^2) a constant velocity of 11 ms^1 would become indiscernable in just over a second (assuming we start from a non existent rest frame of 0 ms^1), like the slightly floaty feeling we have briefly as an express elevator begins its descent, thereafter - as in an express elevator (until it slows to its stop) everything would seem utterly and completely normal (as indeed it does, in an express elevator).

Edited by Einion Yrth on Saturday 30th April 21:02

You've confused acceleration with velocity... unless you've deleted this already?

[Einion Yrth]

deeen said:

Einion Yrth said:

deeen said:

Einion Yrth said:

All inertial frames of reference are equivalent; this really isn't up for discussion, at least not without some serious mathematical backup. An escalator, or elevator, or car, bus, aeroplane, swallow (european or african) that is not undergoing acceleration, is in an inertial frame. The equations by which we can predict motion, work, and energy (potential and kinetic) remain the same in any and all inertial frames, this is not news dammit.

Oh, please yourselves.

Agreed, for horizontal straight line travel. But a vwertical frame of referene (elevator) is affected by gravity. Example... if the elevator drops at a staedy velocity of 11/metres per second, do you think the human inside could detect the movement?

No.Assuming 1 standard g (9.8 ms^2) a constant velocity of 11 ms^1 would become indiscernable in just over a second (assuming we start from a non existent rest frame of 0 ms^1), like the slightly floaty feeling we have briefly as an express elevator begins its descent, thereafter - as in an express elevator (until it slows to its stop) everything would seem utterly and completely normal (as indeed it does, in an express elevator).

Edited by Einion Yrth on Saturday 30th April 21:02

You've confused acceleration with velocity... unless you've deleted this already?

Is the elevator accelerating downwards at 11 ms^2 (answer 1) or moving downwards at 11 ms^1 (answer 2). At some point one or both of us has confused acceleration with velocity. Please restate the question and I'll tell you whether answer 1, or answer 2 applies. "a staedy velocity of 11/metres per second" suggests 11 ms^-1 in which case answer 2 applies and it's you who has confused acceleration with velocity, but I'm happy to dicker. (for a short while, I'm getting tired).

[Tango13]

Just watching the opening scenes of 'You Only Live Twice'

Bond requests permission to come aboard the submarine, what if permission is denied? Would he be fired straight out the torpedo tubes bypassing his interview with 'M'?

[Iva Barchetta]

Willy Nilly said:

Probably one for the high performance car driving PH gods.... Has anyone ever successfully overtaken a Merc Sprinter?

Yes,because round that London they're all way overweight and and struggling to do 30 MPH.

[deeen]

Einion Yrth said:

deeen said:

Einion Yrth said:

deeen said:

Einion Yrth said:

All inertial frames of reference are equivalent; this really isn't up for discussion, at least not without some serious mathematical backup. An escalator, or elevator, or car, bus, aeroplane, swallow (european or african) that is not undergoing acceleration, is in an inertial frame. The equations by which we can predict motion, work, and energy (potential and kinetic) remain the same in any and all inertial frames, this is not news dammit.

Oh, please yourselves.

Agreed, for horizontal straight line travel. But a vwertical frame of referene (elevator) is affected by gravity. Example... if the elevator drops at a staedy velocity of 11/metres per second, do you think the human inside could detect the movement?

No.Assuming 1 standard g (9.8 ms^2) a constant velocity of 11 ms^1 would become indiscernable in just over a second (assuming we start from a non existent rest frame of 0 ms^1), like the slightly floaty feeling we have briefly as an express elevator begins its descent, thereafter - as in an express elevator (until it slows to its stop) everything would seem utterly and completely normal (as indeed it does, in an express elevator).

Edited by Einion Yrth on Saturday 30th April 21:02

You've confused acceleration with velocity... unless you've deleted this already?

Is the elevator accelerating downwards at 11 ms^2 (answer 1) or moving downwards at 11 ms^1 (answer 2). At some point one or both of us has confused acceleration with velocity. Please restate the question and I'll tell you whether answer 1, or answer 2 applies. "a staedy velocity of 11/metres per second" suggests 11 ms^-1 in which case answer 2 applies and it's you who has confused acceleration with velocity, but I'm happy to dicker. (for a short while, I'm getting tired).

The elevator is not accelerating. It is moving down at a velocity of 11 m/s. The person inside knows it is moving, 'cos he is still stuck to the ceiling.

In a horizontal, straight line frame of reference, you would be correct, but (assuming we are on Earth) the vertical vector always includes gravity.

[Einion Yrth]

deeen said:

Einion Yrth said:

deeen said:

Einion Yrth said:

deeen said:

Einion Yrth said:

All inertial frames of reference are equivalent; this really isn't up for discussion, at least not without some serious mathematical backup. An escalator, or elevator, or car, bus, aeroplane, swallow (european or african) that is not undergoing acceleration, is in an inertial frame. The equations by which we can predict motion, work, and energy (potential and kinetic) remain the same in any and all inertial frames, this is not news dammit.

Oh, please yourselves.

Agreed, for horizontal straight line travel. But a vwertical frame of referene (elevator) is affected by gravity. Example... if the elevator drops at a staedy velocity of 11/metres per second, do you think the human inside could detect the movement?

No.Assuming 1 standard g (9.8 ms^2) a constant velocity of 11 ms^1 would become indiscernable in just over a second (assuming we start from a non existent rest frame of 0 ms^1), like the slightly floaty feeling we have briefly as an express elevator begins its descent, thereafter - as in an express elevator (until it slows to its stop) everything would seem utterly and completely normal (as indeed it does, in an express elevator).

Edited by Einion Yrth on Saturday 30th April 21:02

You've confused acceleration with velocity... unless you've deleted this already?

Is the elevator accelerating downwards at 11 ms^2 (answer 1) or moving downwards at 11 ms^1 (answer 2). At some point one or both of us has confused acceleration with velocity. Please restate the question and I'll tell you whether answer 1, or answer 2 applies. "a staedy velocity of 11/metres per second" suggests 11 ms^-1 in which case answer 2 applies and it's you who has confused acceleration with velocity, but I'm happy to dicker. (for a short while, I'm getting tired).

The elevator is not accelerating. It is moving down at a velocity of 11 m/s. The person inside knows it is moving, 'cos he is still stuck to the ceiling.

In a horizontal, straight line frame of reference, you would be correct, but (assuming we are on Earth) the vertical vector always includes gravity.

The person inside is accelerating at 9.8 ms^2. (assuming as always 1 standard g)

v = u + at

assume u = 0, for argument (and cause it makes no real difference)

after 5 seconds the only thing stopping him doing 98 ms^1, "downwards" is the floor of the elevator; he's happily moving around, experiencing 1g and having fun filling out the forms and playing with the pencils on the bench there.

[Jonboy_t]

I've been wondering for a while - who gives a flying fk about a ing fking escalator?

[deeen]

Einion Yrth said:

The person inside is accelerating at 9.8 ms^2. (assuming as always 1 standard g)

v = u + at

assume u = 0, for argument (and cause it makes no real difference)

after 5 seconds the only thing stopping him doing 98 ms^1, "downwards" is the floor of the elevator; he's happily moving around, experiencing 1g and having fun filling out the forms and playing with the pencils on the bench there.

I must admit I was wrong, he is not still stuck to the ceiling.

However if the elevator is still moving down at a steady velocity, he is not experiencing 1g either, so he can detect that the eleveator is moving...

Eg... Compared to a man standing still at ground level, he will feel lighter. His weight, as maeasured by a calibrated spring- loaded scale will be less, although his mass will be the same. I would have to resort to google to give you figures.

[Funkycoldribena]

Jonboy_t said:

I've been wondering for a while - who gives a flying fk about a ing fking escalator?

Open your mind and it all becomes clear.
X-y(2)x6+v = downward force x6(ny)v7xy velocity.

[RobinOakapple]

SpeckledJim said:

singlecoil said:

SpeckledJim said:

3) If it is harder to walk up a stationary staircase than a reversing escalator, because you are gaining height, is it then harder still to walk up an escalator that is moving in the same direction you are, because you are gaining more height?

3) It's harder to walk up an up escalator that it is to stand still on it, but not harder to walk up one than it is to walk up a static one.

Surely you can see your 3) is a nonsense?

How can an escalator moving in one direction have a measurable effect on a body, which then disappears to zero when you reverse the direction of the movement?

Reverse the movement, reverse the effect, no?

Unless there is no effect...

How is it a nonsense?

Of course it is harder to walk up an up escalator than it is to stand still on it, and of course it isn't harder to walk up an up escalator than it is to walk up a stationary one. Perhaps you are thinking that the person in each case needs to move at the same overall speed? i.e. escalator 2mph, person walking up it 2mph therefore overall speed 4mph, walking up a stationary one at 4mph would then of course be harder than achieving overall speed of 4mph on the moving one.

But that's not what he said, though if that is what you had in mind I can see where you are getting confused.

[eliot]

moustachebandit said:

During WW2 we had warning systems to let us know of an impending attack. I was just wondering do we have something like that still in place now?

So if Aliens decided to attack will air raid sirens go off so we can all run for cover or will the first notification we get about it be on the TV?

System has gone now after the end of the cold war.
The bbc would broadcast something but no sirens would sound.
As a child of the 70-80's I was always terrified that the siren on top of the local fire station would go off.
Given that the info is now over 30 years old, it's no longer secret,This website explains in great detail how the network of Bunkers and sirens worked:
http://www.ringbell.co.uk/ukwmo/Index.htm

[SpeckledJim]

RobinOakapple said:

SpeckledJim said:

singlecoil said:

SpeckledJim said:

3) If it is harder to walk up a stationary staircase than a reversing escalator, because you are gaining height, is it then harder still to walk up an escalator that is moving in the same direction you are, because you are gaining more height?

3) It's harder to walk up an up escalator that it is to stand still on it, but not harder to walk up one than it is to walk up a static one.

Surely you can see your 3) is a nonsense?

How can an escalator moving in one direction have a measurable effect on a body, which then disappears to zero when you reverse the direction of the movement?

Reverse the movement, reverse the effect, no?

Unless there is no effect...

How is it a nonsense?

Of course it is harder to walk up an up escalator than it is to stand still on it, and of course it isn't harder to walk up an up escalator than it is to walk up a stationary one. Perhaps you are thinking that the person in each case needs to move at the same overall speed? i.e. escalator 2mph, person walking up it 2mph therefore overall speed 4mph, walking up a stationary one at 4mph would then of course be harder than achieving overall speed of 4mph on the moving one.

But that's not what he said, though if that is what you had in mind I can see where you are getting confused.

Take the second part of the 3).

He is saying a reversing escalator reduces energy expenditure, but a forward escalator doesnt increase it.

How can that make any sense?

What physical principles only apply in one direction?

[RobinOakapple]

SpeckledJim said:

RobinOakapple said:

SpeckledJim said:

singlecoil said:

SpeckledJim said:

3) If it is harder to walk up a stationary staircase than a reversing escalator, because you are gaining height, is it then harder still to walk up an escalator that is moving in the same direction you are, because you are gaining more height?

3) It's harder to walk up an up escalator that it is to stand still on it, but not harder to walk up one than it is to walk up a static one.

Surely you can see your 3) is a nonsense?

How can an escalator moving in one direction have a measurable effect on a body, which then disappears to zero when you reverse the direction of the movement?

Reverse the movement, reverse the effect, no?

Unless there is no effect...

How is it a nonsense?

Of course it is harder to walk up an up escalator than it is to stand still on it, and of course it isn't harder to walk up an up escalator than it is to walk up a stationary one. Perhaps you are thinking that the person in each case needs to move at the same overall speed? i.e. escalator 2mph, person walking up it 2mph therefore overall speed 4mph, walking up a stationary one at 4mph would then of course be harder than achieving overall speed of 4mph on the moving one.

But that's not what he said, though if that is what you had in mind I can see where you are getting confused.

Take the second part of the 3).

He is saying a reversing escalator reduces energy expenditure, but a forward escalator doesnt increase it.

How can that make any sense?

What physical principles only apply in one direction?

Well you must be reading between the lines then, because I can't see where he's written what you are claiming. Hopefully he will come along (if he hasn't got fed up of this topic) and make himself clear (seems clear enough to me though).

[singlecoil]

To pick up on a point RO made, I have to assume SJ is thinking of the overall speed of the person travelling in relation to a fixed point outside the escalator, and I meant a person travelling at a fixed speed in relation to the escalator itself. I trust that clears that up.

SJ- Let's imagine that there are strain gauges fitted to the sole of each of escalator man's shoes, and a recording device in his pocket and outputted to against time plotted on a graph. Do you think they would show the same readings for the climbing man on the static escalator as when he is keeping station on the down one?

[everyeggabird]

It was said that Concorde could fly faster than a bullet. ( Waiting for bearded replies discussing various speeds of bullets).

If one was stood at the back of the plane and fired a shot would you catch up with the bullet?

[singlecoil]

everyeggabird said:

It was said that Concorde could fly faster than a bullet. ( Waiting for bearded replies discussing various speeds of bullets).

If one was stood at the back of the plane and fired a shot would you catch up with the bullet?

I would think that if the plane was travelling at a steady speed then that speed would be added to the speed of the bullet. So my guess is that the answer is no.