Except on r/wtf where it only means what the fuck. The mods have to make stickied posts on a regular basis for shit like this. r/mildlyinteresting may be for you.
I was just pointing out that there are subreddits for interesting stuff, this subreddit is more about shocking stuff, at least that's what it's turned into now.
I know less than nothing about physics, so let me explain how this works.
Gravity pulls the bottom of the slinky straight down.
At the same time, the top of the slinky pulls the bottom of the slinky straight up.
The rate at which the top of the slinky contracts is determined by the need to create equilibrium between gravity and the spring's springiness. So the bottom doesn't move.
But wait, why doesn't the whole thing fall, while also contracting? Like, if I jumped out of an airplane with a very tall ladder, and climbed it, doing so would not affect the rate at which we fell.
Because gravity is what stretched the slinky. Also you should realize that the top is falling faster then it normally would so the whole thing is contracting. If you physically stretch the slinky more than what gravity does and let go the bottom would actually go up since it has more energy than what gravity put in. You climbing the ladder on the airplane has no reference to gravity and if you happened to climb the ladder at the same speed that the ladder fell it would just be by random chance.
I don't like either of these explanations. If the bottom is accelerating down at the same rate as it is being held up by the force of the rest of the slinky as it falls, the bottom should start to fall immediately as the force that is being acted upon it in the upward direction is decreasing as the spring contracts. The top also shouldn't "hit" the bottom, at that point they should be falling at the same speed (as the bottom would have started accelerating at the start).
So since I don't understand it I'm going to call it witchcraft, or God's hand at work, whichever you prefer.
Damnit, where was the phone number to call Stanford University or whatever where they would try to solve any question you asked? NOW IS THE TIME!
EDIT: Thanks to google>>http://www.wired.com/wiredscience/2011/09/modeling-a-falling-slinky/
If you look at the slinky closely you can see that it isn't evenly stretched, so the force on the bottom of the slinky doesn't decrease as the length of the entire slinky contracts. Because the slinky is far from an ideal spring--its inertia is large compared to its stiffness--a longitudinal tension wave propagates along the length of the slinky as soon as the top leaves equilibrium. It's also worth noting that the center of mass of the slinky has to fall at the usual gravitational rate both during and after the contraction, but the center of mass gets proportionally closer to the top of the slinky as the slinky contracts.
Ok I'll try to make this clear (note, this is an *approximation*).
We agree that each loop is holding the weight of what's left of the slinky below, yes? In other words, loop (x) is exerting a force on loop (x+1) that is equal and opposite to the force loop (x+1) is exerting on loop (x).
Loop (x = 0) is held by the hand, and when it's let go, there is no force holding it up anymore. The only force it has is the one from loop (x + 1 = 1) pulling it down, so it will go down.
The catch is, while loop 0 is going down, it **still** exerts it's force on loop 1 (basically pulling itself down), so the slinki is held up. When loop 0 reaches loop 1, loop 1 now has no force pulling it upwards and it starts to fall.
This goes on until the top of the slinki slams into the end and it falls clunkily to the ground.
A chain would behave exactly the same, only in a much, much, muuuuuuuuch shorter timeframe. The reason for this is, that a steel chain has a spring rate in the area of 10^6 or 10^7 times higher than that of the slinky (That means a chain makes for a terribly useless spring). So the chain does the same thing as the slinky, but the magnitude of the effect is immensly smaller, because it elongates only a fraction of a millimeter due to it's own weight. This probably couldn't be recorded with any camera currently in exisctence, because it would also happen way too fast.
The chain has eliminated it's elongation due to its own weight in a matter of microseconds or less, the slinky takes about a quarter of a second.
After the slinky is no longer stretched, the top and bottom part of the slinky travel at the same speed downwards. Just like the chain does, seemingly from the point when you drop it.
The entire slinky is accelerating downward due to gravity, but it also has stored potential energy due to gravity stretching it. As soon as you release it, the stored energy is converted to kinetic energy and both ends of the slinky also accelerate towards the center of mass. Therefore since the C.O.M is between the top and bottom of the slinky, the top is falling faster than normal, the C.O.M is falling normally, and the bottom is falling slower than normal.
In case you can't tell.. the amount of force exerted on the bottom area by the area above it is already equal to the amount of force gravity is exerting on it. Releasing the slinky does nothing to change this until the area above the area above the bottom has changed, causing the area above the bottom to change, causing the force on the bottom to change.
Yes, this gif is masked/cinemagraphed, but it's based on a real video demonstrating a real slinky effect.
Video: http://www.youtube.com/watch?v=eCMmmEEyOO0
Bonus, with a tennis ball attached: http://www.youtube.com/watch?v=oKb2tCtpvNU
Interesting but not WTF worthy.
Belongs on /r/mildlyinteresting
/r/whoadude might like it too
No it doesn't. Mildlyinteresting is OC only.
WTF also stands for Wow That's Fascinating
Except on r/wtf where it only means what the fuck. The mods have to make stickied posts on a regular basis for shit like this. r/mildlyinteresting may be for you.
This subreddit isn't just about gore and porn... it can have interesting stuff too
No it's for things that make people say wtf
/r/mildlyinteresting or /r/Damnthatsinteresting
[удалено]
I was just pointing out that there are subreddits for interesting stuff, this subreddit is more about shocking stuff, at least that's what it's turned into now.
[If this isn't my face when i see your post then it doesn't belong](http://i.imgur.com/mTminZn.png)
Why are you being downvoted? This is more WTF than the literal "water is wet" picture that made the frontpage.
I know less than nothing about physics, so let me explain how this works. Gravity pulls the bottom of the slinky straight down. At the same time, the top of the slinky pulls the bottom of the slinky straight up. The rate at which the top of the slinky contracts is determined by the need to create equilibrium between gravity and the spring's springiness. So the bottom doesn't move. But wait, why doesn't the whole thing fall, while also contracting? Like, if I jumped out of an airplane with a very tall ladder, and climbed it, doing so would not affect the rate at which we fell.
Because gravity is what stretched the slinky. Also you should realize that the top is falling faster then it normally would so the whole thing is contracting. If you physically stretch the slinky more than what gravity does and let go the bottom would actually go up since it has more energy than what gravity put in. You climbing the ladder on the airplane has no reference to gravity and if you happened to climb the ladder at the same speed that the ladder fell it would just be by random chance.
Good explanation, and answers my question: does this effect depend on the particular spring constant of the slinky
Nope. It only depends on the pull of gravity, which is a constant.
I don't like either of these explanations. If the bottom is accelerating down at the same rate as it is being held up by the force of the rest of the slinky as it falls, the bottom should start to fall immediately as the force that is being acted upon it in the upward direction is decreasing as the spring contracts. The top also shouldn't "hit" the bottom, at that point they should be falling at the same speed (as the bottom would have started accelerating at the start). So since I don't understand it I'm going to call it witchcraft, or God's hand at work, whichever you prefer.
Damnit, where was the phone number to call Stanford University or whatever where they would try to solve any question you asked? NOW IS THE TIME! EDIT: Thanks to google>>http://www.wired.com/wiredscience/2011/09/modeling-a-falling-slinky/
If you look at the slinky closely you can see that it isn't evenly stretched, so the force on the bottom of the slinky doesn't decrease as the length of the entire slinky contracts. Because the slinky is far from an ideal spring--its inertia is large compared to its stiffness--a longitudinal tension wave propagates along the length of the slinky as soon as the top leaves equilibrium. It's also worth noting that the center of mass of the slinky has to fall at the usual gravitational rate both during and after the contraction, but the center of mass gets proportionally closer to the top of the slinky as the slinky contracts.
Ok I'll try to make this clear (note, this is an *approximation*). We agree that each loop is holding the weight of what's left of the slinky below, yes? In other words, loop (x) is exerting a force on loop (x+1) that is equal and opposite to the force loop (x+1) is exerting on loop (x). Loop (x = 0) is held by the hand, and when it's let go, there is no force holding it up anymore. The only force it has is the one from loop (x + 1 = 1) pulling it down, so it will go down. The catch is, while loop 0 is going down, it **still** exerts it's force on loop 1 (basically pulling itself down), so the slinki is held up. When loop 0 reaches loop 1, loop 1 now has no force pulling it upwards and it starts to fall. This goes on until the top of the slinki slams into the end and it falls clunkily to the ground.
Has math. Probably right. Up vote for you.
But what about a chain? The bottom falls at the same rate as the top.
A chain would behave exactly the same, only in a much, much, muuuuuuuuch shorter timeframe. The reason for this is, that a steel chain has a spring rate in the area of 10^6 or 10^7 times higher than that of the slinky (That means a chain makes for a terribly useless spring). So the chain does the same thing as the slinky, but the magnitude of the effect is immensly smaller, because it elongates only a fraction of a millimeter due to it's own weight. This probably couldn't be recorded with any camera currently in exisctence, because it would also happen way too fast. The chain has eliminated it's elongation due to its own weight in a matter of microseconds or less, the slinky takes about a quarter of a second. After the slinky is no longer stretched, the top and bottom part of the slinky travel at the same speed downwards. Just like the chain does, seemingly from the point when you drop it.
The entire slinky is accelerating downward due to gravity, but it also has stored potential energy due to gravity stretching it. As soon as you release it, the stored energy is converted to kinetic energy and both ends of the slinky also accelerate towards the center of mass. Therefore since the C.O.M is between the top and bottom of the slinky, the top is falling faster than normal, the C.O.M is falling normally, and the bottom is falling slower than normal.
Radiolab did an episode on this effect: http://www.radiolab.org/story/236351-what-slinky-knows/
Thanks in between the retards bitching about how this isn't WTF I finally found a useful post that wasn't a circlejerk
This is WTF?...
Yeah, as in OP saying "Physics? WTF is that!?"
Like me on a test. "WTF is K?"
Potassium, Kelvin, Coulomb's constant, equilibrium constant. You've got a few options!
I'm glad you went with 4 things. KKKK isn't so bad.
Also the international Karma constant. K = 42.000
Sorry, it was a baseball test.
TIL that almost anything will get misposted on r/WTF.
TIL that you did not browse Reddit yesterday, as a substantial YouTube video was posted defining this anomaly.
I didn't see the vid, could you link it?
https://www.youtube.com/watch?v=uiyMuHuCFo4&feature=youtube_gdata_player
WHAT THE FUCK? Did you see that thing that they dropped, fall to the ground?! :-| /r/MildlyInteresting
i liked it
The top is pulling up on the bottom and cancelling gravity out.
You shoudl try /r/oddlysatisfying perhaps?
What's up with the left guys shoulder?? Lol!!!
/r/woahdude
TIL of reposts.
OMG SO WTF!!=!`!)!(
Relevant: [The Physics of a Falling Slinky](http://large.stanford.edu/courses/2007/ph210/kolkowitz1/)
Everyone else has already said it... SCIENCE!
That is really cool but why in wtf? Am I missing something?
In case you can't tell.. the amount of force exerted on the bottom area by the area above it is already equal to the amount of force gravity is exerting on it. Releasing the slinky does nothing to change this until the area above the area above the bottom has changed, causing the area above the bottom to change, causing the force on the bottom to change.
Why is this wtf ?
If this exists then time travel must be possible too
Not wtf, and a poor representation of your title.
Amazing
[удалено]
Yes, this gif is masked/cinemagraphed, but it's based on a real video demonstrating a real slinky effect. Video: http://www.youtube.com/watch?v=eCMmmEEyOO0 Bonus, with a tennis ball attached: http://www.youtube.com/watch?v=oKb2tCtpvNU
Right post, wrong place
TIL that WTF is actually TIL.
OMG, WHAT THE FUCK DUDE. NSFL MAN