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

[singlecoil]

deeen said:

singlecoil said:

That's the basis of your misunderstanding. If you stay in one place you are NOT going from -2mph to zero. You are already at zero. All you have to do is to move your legs to accommodate the movement of the escalator. The moving part of your legs is less than half your body weight, therefore the work done is less than half that of walking up a static escalator.

Imagine 2 down escalators next to each other, each with a man standing at the same point, near the top. Those men have the same potential energy from gravity.

One stands still, and ends up at the bottom of the escalator. The other climbs at the rate needed to match the speed of the escalator, and stays in the same place.

Now, those two men have different potential energy. The difference is the kinetic energy used by the man who "stays in the same place".

Indeed. The original question was about comparing the energy consumption between a man staying in the same place on a down escalator, and another climbing a static escalator. The latter will have more potential energy that the former. The difference is the kinetic energy used by the latter.

[RobinOakapple]

popeyewhite said:

Uh-huh.





Sorry.

Don't know what you are laughing for, you've had your head nailed to the coffee table

[Dr Jekyll]

If someone made a fast run up to the edge of a cliff or a very high diving board before jumping out into space. Roughly how far would they travel horizontally before the dive became vertical?

[Einion Yrth]

deeen said:

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.)...

You can if it's moving fast enough for your body to feel the apparant reduction in gravity. You can measure it at any speed. The only reason you might not feel it in a "normal" lift is that your body is not that sensetive to small variations in gravity.

There is only any difference in "gravity" if the thing is accelerating. That's the whole point. As an elevator (which is a perfectly adequate analogy for an escalator, thank you) accelerates from rest we do feel a change in weight, so that puts that one to bed, then as it continues at a fixed rate we feel the "right" weight and it would be impossible to tell whether or not we are moving, until the stop at the bottom when, as we decelerate, we momentarily feel heavier.

[RobinOakapple]

Einion Yrth said:

There is only any difference in "gravity" if the thing is accelerating. That's the whole point.As an elevator (which is a perfectly adequate analogy for an escalator, thank you) accelerates from rest we do feel a change in weight, so that puts that one to bed, then as it continues at a fixed rate we feel the "right" weight and it would be impossible to tell whether or not we are moving, until the stop at the bottom when, as we decelerate, we momentarily feel heavier.

Have to correct you there, it's not an analogy at all in the context of my original question. To be an analogy there would have to be some means whereby the occupant could, by moving his legs, overcome the downward motion of the lift, and there isn't any such means. OTOH, on an escalator it's perfectly possible to maintain position and even make upward progress on a down escalator.

[RobinOakapple]

Dr Jekyll said:

If someone made a fast run up to the edge of a cliff or a very high diving board before jumping out into space. Roughly how far would they travel horizontally before the dive became vertical?

If there was no air movement or resistance then the motion would be a complex vector of the forces involved. With no other forces apart from gravity then it would be a curve. When it became vertical would be defined by how closely you were able to measure the forward motion.

[Einion Yrth]

RobinOakapple said:

Einion Yrth said:

There is only any difference in "gravity" if the thing is accelerating. That's the whole point.As an elevator (which is a perfectly adequate analogy for an escalator, thank you) accelerates from rest we do feel a change in weight, so that puts that one to bed, then as it continues at a fixed rate we feel the "right" weight and it would be impossible to tell whether or not we are moving, until the stop at the bottom when, as we decelerate, we momentarily feel heavier.

Have to correct you there, it's not an analogy at all in the context of my original question. To be an analogy there would have to be some means whereby the occupant could, by moving his legs, overcome the downward motion of the lift, and there isn't any such means. OTOH, on an escalator it's perfectly possible to maintain position and even make upward progress on a down escalator.

Make it infinitely high and stick a ladder on the wall. Everything else applies.

[Einion Yrth]

RobinOakapple said:

Dr Jekyll said:

If someone made a fast run up to the edge of a cliff or a very high diving board before jumping out into space. Roughly how far would they travel horizontally before the dive became vertical?

If there was no air movement or resistance then the motion would be a complex vector of the forces involved. With no other forces apart from gravity then it would be a curve. When it became vertical would be defined by how closely you were able to measure the forward motion.

With no air resistance it would tend asymptotically towards vertical, but could never actually become vertical because your horizontal velocity would remain constant.

[RobinOakapple]

Einion Yrth said:

RobinOakapple said:

Einion Yrth said:

There is only any difference in "gravity" if the thing is accelerating. That's the whole point.As an elevator (which is a perfectly adequate analogy for an escalator, thank you) accelerates from rest we do feel a change in weight, so that puts that one to bed, then as it continues at a fixed rate we feel the "right" weight and it would be impossible to tell whether or not we are moving, until the stop at the bottom when, as we decelerate, we momentarily feel heavier.

Have to correct you there, it's not an analogy at all in the context of my original question. To be an analogy there would have to be some means whereby the occupant could, by moving his legs, overcome the downward motion of the lift, and there isn't any such means. OTOH, on an escalator it's perfectly possible to maintain position and even make upward progress on a down escalator.

Make it infinitely high and stick a ladder on the wall. Everything else applies.

It certainly would. In fact, as it obviously wouldn't have a roof, it would be a vertical escalator. Any thoughts on the original question?

RobinOakapple said:

Does walking up a stationary escalator require more energy than staying in the same place on an escalator that is going down (assuming that the escalator in the second part is running at the same speed as the person is the first part)?

[Dr Jekyll]

Einion Yrth said:

With no air resistance it would tend asymptotically towards vertical, but could never actually become vertical because your horizontal velocity would remain constant.

Yes, but the reason I ask the question is that there would be air resistance so the drop would become vertical. To put it another way, how much horizontal motion would take place before air resistance slowed the horizontal speed to zero?

[RobinOakapple]

Dr Jekyll said:

Einion Yrth said:

With no air resistance it would tend asymptotically towards vertical, but could never actually become vertical because your horizontal velocity would remain constant.

Yes, but the reason I ask the question is that there would be air resistance so the drop would become vertical. To put it another way, how much horizontal motion would take place before air resistance slowed the horizontal speed to zero?

Anyone up to calculating that will need to know the weight of the jumper, his speed at takeoff and the various factors that make up the air resistance or drag, and probably other stuff as well. I expect. Certainly a compact weighty person with a good launch speed will travel further than for instance Keira Knightley in a ballgown.

[popeyewhite]

RobinOakapple said:

Does walking up a stationary escalator require more energy than staying in the same place on an escalator that is going down (assuming that the escalator in the second part is running at the same speed as the person is the first part)?

No. Go and try it instead of wittering on. So much like the plane on a moving belt 'paradox' (to some), except this one's easily personally demonstrable.

[RobinOakapple]

popeyewhite said:

RobinOakapple said:

Does walking up a stationary escalator require more energy than staying in the same place on an escalator that is going down (assuming that the escalator in the second part is running at the same speed as the person is the first part)?

No. Go and try it instead of wittering on. So much like the plane on a moving belt 'paradox' (to some), except this one's easily personally demonstrable.

You've ignored the explanations given in favour of your usual adversarial style.

[talksthetorque]

Einion Yrth said:

Make it infinitely high and stick a ladder on the wall. Everything else applies.

How would you have an infinitely high lift compartment?
Where would it go?

[popeyewhite]

RobinOakapple said:

You've ignored the explanations given in favour of your usual adversarial style.

Weak.

[RobinOakapple]

popeyewhite said:

RobinOakapple said:

You've ignored the explanations given in favour of your usual adversarial style.

Weak.

The basic fact that anyone insisting that the energy consumption will be the same is the fact that, as pointed out earlier by Deeen, is that at the end of the exercise the person climbing will have more potential energy than the person who stays in the same place. That energy has to come from somewhere, it's really very basic physics.

Height gained means work has been done. The person on the down escalator is only having to raise his legs to counter the downward motion so his legs are gaining height but the rest of his body is not. Therefore the climber does more work than the person staying in the same place because more mass has gained height.

[SpeckledJim]

RobinOakapple said:

popeyewhite said:

RobinOakapple said:

You've ignored the explanations given in favour of your usual adversarial style.

Weak.

The basic fact that anyone insisting that the energy consumption will be the same is the fact that, as pointed out earlier by Deeen, is that at the end of the exercise the person climbing will have more potential energy than the person who stays in the same place. That energy has to come from somewhere, it's really very basic physics.

Height gained means work has been done. The person on the down escalator is only having to raise his legs to counter the downward motion so his legs are gaining height but the rest of his body is not. Therefore the climber does more work than the person staying in the same place because more mass has gained height.

The person staying still is putting energy into the downward motion of the escalator. He is helping it descend.

That energy matches the gain in potential energy of the ascending man.

[Speed 3]

In light of this sad murder case and many others,

http://www.bbc.co.uk/news/uk-england-36172473

Where does the boundary lie in a legal/moral sense of responsibility when there is a spectrum covering insanty, psychosis, temporary/permanent ?

In my simplistic view is it just if you are deemed "insane" its a secure hospital rather than a prison ?

Edited by Speed 3 on Saturday 30th April 15:39

[popeyewhite]

SpeckledJim said:

The person staying still is putting energy into the downward motion of the escalator. He is helping it descend.

Yes, very slightly, which is why Olympic coaches suggest a slight resistance on the steps to compensate. It is similar to the 'treadmill vs. running' argument: Some recommend putting a slight incline on a treadmill when running to counter the 'pulling back' effect of the belt. However the counter-argument is the belt forces longer gait and therefore effort increases. Calorie expenditure research has been completed with some results suggesting slightly more calories expended over a 20 minute period for the person climbing actual stairs. Some results have shown greater calorie expenditure for the step machine. Factors such as muscle strength, speed of climb etc are pertinent. The biomechanics of the two are almost identical, but more muscles are used on the step machine as the person tends to lean forwards slightly more.

[Dr Jekyll]

Speed 3 said:

In light of this sad murder case and many others,

http://www.bbc.co.uk/news/uk-england-36172473

Where does the boundary lie in a legal/moral sense of responsibility when there is a spectrum covering insanty, phsycosis, temporary/permanent ?

In my simplistic view is it just if you are deemed "insane" its a secure hospital rather than a prison ?

This is no doubt oversimplified but what a lawyer friend told me is that it hinges on whether it's a case of 'guilty but insane' or 'not guilty due to insanity'.

Shoot your neighbour because you think he is Lord Lucan, guilty because shooting Lord Lucan is still illegal, but insane. So a secure hospital rather than prison. Shoot him because you think he is a man eating tiger, not guilty due to insanity. So prison doesn't arise but you would probably be sectioned. The hospital may well be pretty secure but as an alternative to a normal hospital not an alternative to prison.