Can the speed of an escalator be varied?
I mean, say we find someone who works the night shift cleaning some place that has one. We fix the whole possibility of it slipping and of the correct size slinky for the stairs. Now, is there a speed variation knob in the controls somewhere?
The stairclimber examples Rick put up seem a bit too small to be a useful test… Maybe if we could find a larger example like it?
And what if the escalator was on a treadmill?
:: d&r ::
I think the slinky would stop slinking fairly quickly on an escalator. The motion that keeps it going is the downward energy being transferred rotationally in a forward flip that helps it continually clear the next stair. Even on a stationary staircase of infinite length, eventually friction will cause the slinky eventually to strike a point closer and closer to the previous stair until it can no longer clear the next ledge. An escalator presents a further problem because it is adding backward acceleration that a stationary stair does not.
Seriously, did any of you guys honestly think a slinky was some kind of frictionless perpetual motion machine? I’m really surprised.
::: scratches head:::
Huh? Once you hit the on switch the stairclimber becomes and endless staircase. If it is endless, how can it be to small?
I don’t get it.
This isn’t a perpetual motion thing. The idea is perfectly realistic, physics-wise. The stair surface and the Slinky[sup]TM[/sup] are in an inertial frame that is moving up and sideways relative to the ground. And, that frame has its full complement of gravitational acceleration. With appropriately sized steps and with feedback mechanisms to control the escalator’s speed and perhaps transverse tilt (to keep the Slinky[sup]TM[/sup] steered), one could keep it going forever. (Or until you ran out of power for your escalator.)
If I had more time on my hands I’d love to build such a contraption. A couple of ultrasonic range finders could measure the location of the slinky, and a simple circuit would feed that information back into the stair motor’s speed and into servos that control the tilt of the whole device…
Me either. Your linked-to model looks perfect (assuming the size of the step is okay), although you’d need to configure it to run backwards since the Slinky[sup]TM[/sup] needs to climb down the stairs.
An escalator doesn’t add any acceleration at all. It travels at a constant speed, at least when you’re not adjusting it. From the slinky’s point of reference, the speed of the escalator is irrelevant. It’s going to try to get to that next-lower step despite the fact that that step will be where the current step is when it gets there. I agree that it won’t go on forever, as I don’t think it would go on forever down an infinite stationary staircare, but the fact that the escalator is moving won’t matter.
I don’t think that the examples put up by Rick would work because you would have such a short period of time to adjust the speed or whatever else needs to be done… though I guess it would work, I think that a larger model or a real escalator would give the space required to let the slinky go down well.
Brain Wreck, we really don’t expect the thing to go for years… I’d expect it to go for a couple minutes at the most. It isn’t some search for a perpetual motion machine, its a “hm, bored, lets see what if…”
And Pasta, wow.
Pasta, since you “are” building the escalator just for this. Do you really need all those control gadgets? why not just a very narrow escalator with barriers on both sides (teflon coated, maybe) to keep the Slinky on track?
It seems to me the limiting factor is the energy provided initially to provide forward motion. A slinky just sitting still is stable, won’t go anywhere but you have to sorta… just… you know, do the slinky thing and push it just so and it will end over end (somewhat like a pendulum in a way) until that energy is consumed and it rights itself (or lands on it’s side). Now… you could prolong the ideal environment for the slinky to efficiently use ALL of that energy you provided by giving it a sort of perpetual slinky environment without any obstructions like… the floor, or your cat or your little sister, but eventually it will stop and the escalator will simply carry it to the top floor and deliver it back to you for more fun. I think.
I want this shirt.
And I found a couple of discussions that get pretty in depth here and here.
A working model is described here, but the link to further information is dead. :mad:
This is odd.
Won’t the backwards acceleration actually help us here? It should help the slinky to continue to clear the next tread for longer than on a stationery staircase, no?
I just assumed that the backwards acceleration would have a negligible effect on a slinky as (unless we use Pasta’s model) I assume the slinky would just fall over at some point before that became a real problem.
As Brian Wreck warned and lokij pointed out, there is nothing in the system to provide forward momentum. Gravity only pulls down. The initial kick is all the system has, and that will disappear. The whole contraption (or just each step) would need a slight forward tilt so that gravity can restore whatever forward momentum gets lost in each cycle. (Fortunately, mine’s got servos! 
)
I’m vaguely remembering some high school physics that have to do with springs… Could someone point out some numbers we’ll need to know?
This is the SDMB, so I doubt anybody would be talking perpetual motion. In the coin example I gave, the energy came from a kick-arse three-phase AC electric motor. If my coins hadn’t crashed, they’d have gone on rolling indefinitely.
This thread reminds me of Craig Swanson’s cartoon: “She Came Down the Stairs in her Slinky Dress”.
I’d link to it, but my work computer won’t link to his site. Thinks it’s dangerous or frivolous or something. Just google “Perspicuity slinky dress”. It’s worth it.