Slinky physics question
Discussion
UKBob said:Always hated chaos theory, doesn’t seem to be underlying logic. Is there really such a thing as chaos at all?
Chaos theory (whatever its called) guarantees that the question will be turned on its head - nothing is perfectly made, and the slinky will eventually hit the side, sooner or later. Come on, agree with me. You know Im right
Any way my more immediate concern is that I could build an elevator without sides to stop this from happening (I mean one where the slinky wont fall off the edge).
UKBob said:The point you're missing though is, as anone who has studied Physics at A-level or above knows, is that it is very common to assume a simplified model in order to test a theory. Thus you can consider lossless systems, quasi-static processes, spherical cows, etc.
Chaos theory (whatever its called) guarantees that the question will be turned on its head - nothing is perfectly made, and the slinky will eventually hit the side, sooner or later. Come on, agree with me. You know Im right
Also, what you're referring to isn't so much Chaos Theory as simple entropy.
>> Edited by JonRB on Thursday 8th December 12:22
danielson said:
this is such a great thread.
puts me in mind of Mythbusters, which if you havent already, you should watch. 'tuther day they explored what would happen if you jumped up at the critical moment in a falling lift. with a real lift.
well....
Buster got squished i imagine.
Aye, but consider a regular slinky at the top of ordinary stairs.
The energy input to get it to slink is very minimal, if you hit a slinky on a flat surface, it goes no where.
So it is the conversion of the potential energy (height above the next step) to kinteic energy (supplied by gravity as the slinky falls) that gives the slinky enough kinetic energy to topple to the next step down, and so on.
If the stairs are too high then the spring collects too much kinetic energy and the system goes out of control, if the stair aren't high enough then there isn't enough kinetic energy to get the spring to topple to the next step.
So given that the escalator is rising, and thus constantly supplying potential energy to the system, the slinky would continue until it hits the side, or the spring wears out and breaks.
The step height and speed of the escalator could be tuned to ensure the slinky never stops.
The energy input to get it to slink is very minimal, if you hit a slinky on a flat surface, it goes no where.
So it is the conversion of the potential energy (height above the next step) to kinteic energy (supplied by gravity as the slinky falls) that gives the slinky enough kinetic energy to topple to the next step down, and so on.
If the stairs are too high then the spring collects too much kinetic energy and the system goes out of control, if the stair aren't high enough then there isn't enough kinetic energy to get the spring to topple to the next step.
So given that the escalator is rising, and thus constantly supplying potential energy to the system, the slinky would continue until it hits the side, or the spring wears out and breaks.
The step height and speed of the escalator could be tuned to ensure the slinky never stops.
wizzpig said:
this is such a great thread.
puts me in mind of Mythbusters, which if you havent already, you should watch. 'tuther day they explored what would happen if you jumped up at the critical moment in a falling lift. with a real lift.
well....
Buster got squished i imagine.
what 'ee sed.
in short, unless you could develop the timing of a mountain cat and the ability to jump upwards at the same speed as the lift is descending (60mph) youre arriving in Bedroom Furnishings, Whicker and Assorted Cheeses with a headache.
TheExcession said:
Aye, but consider a regular slinky at the top of ordinary stairs.
The energy input to get it to slink is very minimal, if you hit a slinky on a flat surface, it goes no where.
So it is the conversion of the potential energy (height above the next step) to kinteic energy (supplied by gravity as the slinky falls) that gives the slinky enough kinetic energy to topple to the next step down, and so on.
If the stairs are too high then the spring collects too much kinetic energy and the system goes out of control, if the stair aren't high enough then there isn't enough kinetic energy to get the spring to topple to the next step.
So given that the escalator is rising, and thus constantly supplying potential energy to the system, the slinky would continue until it hits the side, or the spring wears out and breaks.
The step height and speed of the escalator could be tuned to ensure the slinky never stops.
Exactly what he said!
The slinky slinking depends on the top of the slinky having forward momentum at the end of each slink. If we are assuming a frictionless system, then it'll continue to slink as the initial forward (horizontal) momentum will be preserved. If there are losses, then the initial forward momentum will eventually be lost.
Aside on chaos theory - the essence of chaos theory is that the outcome of a system is higly dependent on initial conditions, so a slight variation in the initial parameters will result in a large change in the outcome. The example I usually use is to imagine a drop of water landing on the back of your hand then running off. There are points on your hand where the initial placement of the water drop only has to vary by millimeters to produce completely different results (water rolls to the left instead of the right).
<aside over>
Aside on chaos theory - the essence of chaos theory is that the outcome of a system is higly dependent on initial conditions, so a slight variation in the initial parameters will result in a large change in the outcome. The example I usually use is to imagine a drop of water landing on the back of your hand then running off. There are points on your hand where the initial placement of the water drop only has to vary by millimeters to produce completely different results (water rolls to the left instead of the right).
<aside over>
ewenm said:
Aside on chaos theory - the essence of chaos theory is that the outcome of a system is higly dependent on initial conditions, so a slight variation in the initial parameters will result in a large change in the outcome. The example I usually use is to imagine a drop of water landing on the back of your hand then running off. There are points on your hand where the initial placement of the water drop only has to vary by millimeters to produce completely different results (water rolls to the left instead of the right).
<aside over>
wait, youre jeff goldblum? man, you sucked in Jurrasic Park 2.
ewenm said:
The slinky slinking depends on the top of the slinky having forward momentum at the end of each slink.
Indeed, but again, the energy input to cause the first slink is minimal, and I would agree with you that at some stage (unless i na perfect system) this energy must decay.
However, having spent a long time bouncing slinkys down long stairways I would suggest that the energy required for the first slink does not need to be preserved.
What you are missing from the equation is the fact that an escalator does not go vertivally up, it moves in two dimensions not one. So it is imparting both the forward motion and the vertical motion required for the spring to continue to slink.
As said, it's about adjusting the speed and step height of the escalator such that these forces remain in exactly in equilibrium with the engery input required for the first slink coupled with any losses the system might have.
axeman30 said:
Yep, the rising escalator raises the potential energy of the slinky, the slinky turns this into kinetic energy by dropping to the next step.
Surely friction will also cause a small amount of engery to be lost from the system as heat, over time that will dissapate the engery from the system and the slinky will eventually stop.
no, the friction will cause drag which will increase the work of the escalator motor, which will be seen as an increase in current demand, in the same way as a passenger getting on
Oh c
p
Just had something similar to this on another forum, concerning an aeroplane and a converyor belt runway, runway doing same speed as plane (but in opposite direction) will plane take off?
This ran and ran and ran with yes and no answers and reasons why it would or it wouldn't.
Needless to say, we never did find out a definative answer (unless someone has rigged up the aforementioned conveyor belt and plane)
p Just had something similar to this on another forum, concerning an aeroplane and a converyor belt runway, runway doing same speed as plane (but in opposite direction) will plane take off?
This ran and ran and ran with yes and no answers and reasons why it would or it wouldn't.
Needless to say, we never did find out a definative answer (unless someone has rigged up the aforementioned conveyor belt and plane)
apache said:
Yep, the rising escalator raises the potential energy of the slinky, the slinky turns this into kinetic energy by dropping to the next step.
Surely friction will also cause a small amount of engery to be lost from the system as heat, over time that will dissapate the engery from the system and the slinky will eventually stop.
no, the friction will cause drag which will increase the work of the escalator motor, which will be seen as an increase in current demand, in the same way as a passenger getting on
In which case as the escalator is acting as the external energy source to the slinky-system then I suppose if it's a perfect slinky it would go on forever. In the same way that if you dropped an object from an infinite height it would never stop falling.
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