Escalator Antics
February 17, 2004 4:19 AM   Subscribe

Why is it harder to run/walk up a stopped escalator than a moving one? Surely the step size is the same and your relative speed is the same?
posted by biffa to Science & Nature (24 answers total)
 
Might have something to do with your expectations.
Do you find it harder to go up stopped escalators than stairs?
posted by kenaman at 4:33 AM on February 17, 2004


It's all physics and gravity. (Keep in mind that I haven't done physics since 1999, so I might be rusty.)

In order to move against the direction gravity pulls, you need to exert Fx Newtons of force, where x is a number which I think I've forgotten how to calculate (mass * 9.8? anyone? bueller?) to counteract the amount of force gravity (Fg) exerts on you

Because the escalator already provides a certain amount of force Fy, Fx is naturally lower, because Fg is a constant. So, mathetmatically:

Fg = Fx + Fy

When walking up stationary stairs, Fy has no value. Basic arithmetic proves that the higher the value of Fy, the lower the value of Fx.


Of course, I might be wrong.
posted by cheaily at 4:46 AM on February 17, 2004


kenaman: yes I do find it harder to go up escalators than stairs, I thought everyone does as you can see people having to make those big striding step-ups on a stopped escalator.

cheaily: I would have thought that the escalator doesn't provide any force, its constant speed means that there's no acceleration, so no force (but I could be wrong too).
posted by biffa at 5:03 AM on February 17, 2004


When walking up a running escalator, the escalator carries you part of the way. When it's stopped, you have to do all the work yourself. No physics required.
posted by signal at 5:13 AM on February 17, 2004


biffa: Like I said, I might be wrong ;) It's been a while since I've had to do anything like that. I think i'm confusing the principles of force and work, but i'd have to dig out my old textbooks to make sure, which I really don't feel like doing.

signal: well, yes. that would be the simple explanation for it. *cough* i'm, er, going to go and hide in the corner now.
posted by cheaily at 5:30 AM on February 17, 2004


When the escalator is moving, you have to run up fewer stairs to reach the top than if the escalator is stopped.
posted by mfbridges at 5:47 AM on February 17, 2004


Take steps out of the equation. In most large airports they have moving sidewalks. MSP for instance covers a lot of distance with these things. I have yet to see all of them work on any given trip however. They're placed in pairs, one walkway moves for instance north while the other moves south.

Often only half the pair will be moving. If you sprint down the moving walkway in the direction of travel you'll have sprinted relative to the walkway at the same velocity as you would down the non-moving one.

You're sprinting down over a fixed distance however so when the walkway assists you you're sprinting for less time so less energy is expended, you're less winded etc.

You could sprint with the walkway and against the walkway too to really exacerbate the effect.
posted by substrate at 6:39 AM on February 17, 2004


The energy expended in mumbling "How hard is it to keep a frickin' escalator running?" the whole time.

(The less flippant version of which is: I think perception has a lot to do with it, as kenaman said. When you're conscious of the fact that you're doing work you normally wouldn't have to be doing, it seems more onerous.)
posted by staggernation at 6:57 AM on February 17, 2004


I think the size of the steps makes it more difficult. They are definitely not the standard size for stairs - they're taller.
posted by agregoli at 7:20 AM on February 17, 2004


Substrate said: Take steps out of the equation. . . walkways. . . etc

Yes, but that's irrelevant. Biffa is talking about steps within the closed system of the escalator: thus we could theoretically consider the elevator to be of infinite length, and immobile, while the rest of the world slides down relative to the escalator; the physics would be the same (force, kinetic energy, etc; though I'm waiting for taumeson or someone to come in and correct all of us). In this case he's merely walking up the escalator, just as he would in the real life stopped-escalator example. I'm willing to chalk the perceived difference to the awkwardness of being in motion and not a real physical difference.
posted by The Michael The at 8:05 AM on February 17, 2004


it's not just going up - running down feels different if the escalator is not moving. i thnk your mind is used to predicting where the next step will, assuming that it's moving, and it gets confused when it's not.

ignoring silly little things like air resistance, and psychological things like i just considered, it should make no difference per step whether the escalator is moving or not, as long as it is moving at a constant speed.

however, the total amount of work done in getting from one floor to another will be more if the escalator is stopped as a moving escalator "does some of the work for you" - if the total rise is 15 steps, you probably stride up 10 while the escalator moves 5, so you only did 10 steps worth of work to get to the top, compared with the whole 15 for a stationary escalator.

(note that the difference in energy expended between moving and not moving escalators decreases the faster you run up the steps, because you're on the escalator for less time, and, since the escalator moves at a fixed speed, it contributes less over a shorter interval).
posted by andrew cooke at 8:19 AM on February 17, 2004


Maybe the stairs have more/less give when moving?
posted by callmejay at 8:37 AM on February 17, 2004


It's probably obvious to you why running up the down elevator is more difficult than running up a stopped or up elevator.

The stopped elevator is more difficult than the up elevator for the exact same reason.
posted by five fresh fish at 8:38 AM on February 17, 2004


It's all in yer head:

Because the escalator already provides a certain amount of force Fy, Fx is naturally lower, because Fg is a constant.

I think this is true and, as above, easily proven by physics. Still, I think the amount of upward force from the escalator exercized on the walker is so minimal that the effect is purely psychological. Maybe.

When walking up a running escalator, the escalator carries you part of the way.

Riiight... so, you're expecting to exert as much energy as you would climbing stationary stairs, but your mind is pleasantly surprised when it exerts, say, half that much effort...

But a pin with angels on its head placed on an escalator... ah, now that's a totally different question...
posted by Shane at 10:02 AM on February 17, 2004


Thanks, biffa! Whatever the explanation, the feeling of gravity having doubled when you walk up a stopped escalator is cool and bizarre!
posted by Shane at 10:15 AM on February 17, 2004


so, you're expecting to exert as much energy as you would climbing stationary stairs, but your mind is pleasantly surprised when it exerts, say, half that much effort...

Part actual effort and part optical illusion. You're taking the exact same steps, you're just watching the scenery go by faster, so you're perceiving more progress per step, even though there isn't (though there are less of them).
posted by jalexei at 11:06 AM on February 17, 2004


>cheaily: I would have thought that the escalator doesn't provide any force, its constant speed means that there's no acceleration, so no force (but I could be wrong too
>Maybe the stairs have more/less give when moving?>
It's all in yer head:.
>When walking up a running escalator, the escalator carries you part of the way.


You are talking about stairs and escalator going up, not down, as notice your question when ascending an out of order escalator.
Add to above, an optical allusion when the escalator is not moving, the steps seem to move down when being stepped on. Notice this allusion in bath & toilet rooms that have been wallpapered with small & close vertical stripes. The metal vertical grooves on the escalator's steps makes the allusion the step are moving down when stepping on it. So the fact that the escalator is not moving which is something your not use too, then this added allusion may create: "the more work than stairs".
posted by thomcatspike at 11:08 AM on February 17, 2004


Also, are exsculotor steps wider than stair steps? Check them out at the top or bottom where they become flush with the floor.
posted by thomcatspike at 11:12 AM on February 17, 2004


i'm with agregoli, the steps are just bigger than normal stairs.

also, i think Fy=0 as F=mass*acceleration and ay=0

If an elevator is moving up at a constant velocity you can't jump any higher relative to the insides of the elevator than usual.
posted by rhyax at 11:13 AM on February 17, 2004


I can't figure out why most people stop walking once they reach the escalater rather continue on walking.
posted by brent at 1:12 PM on February 17, 2004


I can't figure out why most people stop walking once they reach the escalater rather continue on walking.

Well, for up escalators I can sort of see it. It's standing on down escalators that stumps me. Unless you have, like, knee trouble or something.
posted by staggernation at 2:05 PM on February 17, 2004


must of miffed my spell check: meant illusion, not allusion, [puts fingers in the closing steps portion of a moving escalator]
posted by thomcatspike at 2:50 PM on February 17, 2004


Someone asked the exact same question in the Sydney Morning Herald's "Big Questions" column last week. The answer provided:

"Escalators generally aren't designed to walk on. The relationship between the depth of the step and the height between steps is important. Most escalators have a tread (the part you stand on) of about 40 centimetres, with a riser (the height between each step) of about 20 to 25 centimetres. This creates a "slope" of about 50 per cent. Stairs usually have a tread of 40 centimetres, but a rise of 15 centimetres, creating a slope of about 38 per cent."

(To give credit where credit is due, that answer was contributed by David Hewetson of Harris Park.)
posted by web-goddess at 3:12 PM on February 17, 2004


The Michael The: Thank you for understanding. I'm pretty sure I'm on track with the physics.
jalaxei 's answer seems reasonable with regard to possible psychological explanation.
posted by biffa at 3:40 PM on February 17, 2004


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