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Awesome HD Slinky Slow-Mo…Does Gravity Really Work Like We Think It Does?
Veritasium ^ | Sept 29, 2012 | Jim Caldwell

Posted on 10/04/2012 4:04:07 PM PDT by jwsea55

Watching this video, I have to ask, do we really understand gravity? When we release an object from our hands, it falls. Right? Not always? Or at least, not right away?

Veritasium has put some pretty cool videos to explain how science and physics work. They have been working with slinkies on a number of videos (and you thought your kid didn’t have any potential at 3 years old), this video seems to capture the essences of their work.

So listening to a couple of science guys explain this, does this give one a solid enough understanding why that darn bottom of the slinky doesn’t move? OK, I get the propagating communication of information thing, and that gravity has a constant force on the center of gravity but when I step back from all that, why doesn’t that slinky’s bottom move? Jim Caldwell


TOPICS: Arts/Photography; Miscellaneous; Science
KEYWORDS: gravity; physics; slinky
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Looked at this a few times. Still find it puzzling.
1 posted on 10/04/2012 4:04:14 PM PDT by jwsea55
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To: jwsea55

Fascinating. Thanks for posting that.


2 posted on 10/04/2012 4:12:34 PM PDT by .45 Long Colt
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To: .45 Long Colt
Thanks.
I just watched a couple of times. Even with an explanation, why doesn't the bottom move?
3 posted on 10/04/2012 4:15:35 PM PDT by jwsea55
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To: jwsea55

My computer has no sound and I do no read lips. I do not know the explanation the guy on the video provided.

The bottom doesn’t move because it is still attached to the rest of the slinky.


4 posted on 10/04/2012 4:24:31 PM PDT by SatinDoll (NATURAL BORN CITZEN: BORN IN THE USA OF CITIZEN PARENTS.)
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To: SatinDoll
My computer has no sound and I do no read lips. I do not know the explanation the guy on the video provided.

The bottom doesn’t move because it is still attached to the rest of the slinky.

Essentially, two science geeks yakking in physic's speak. The bottom doesn't move because of the slinky's tensioned coil. The tension has not allowed the "communication" of release from the top of slinky to transfer down to the bottom. Does that work?

5 posted on 10/04/2012 4:35:02 PM PDT by jwsea55
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To: jwsea55
Awesome is right! I was and still am, a mediocre math student; but I love physics. Wish I would have paid more attention in school.

The closest explanation that I could comprehend in the simplest way, was “external force” on the “center of mass”

6 posted on 10/04/2012 4:52:46 PM PDT by KittenClaws (You may have to fight a battle more than once in order to win it." - Margaret Thatcher)
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To: jwsea55

I’ll try my hypothesis...

The downward pull of the stored tension in the slinky plus gravity is exactly the same as the tension of the slinky thus counteracting the pull of gravity. Once the tension+gravity equalizes to the weight of the slinky alone, the slinky falls at the normal rate of 32 ft.per sec./per sec.

I hope that makes this clearer for you.

If not, well you can say I’m full of $hit.


7 posted on 10/04/2012 4:58:28 PM PDT by Randy Larsen (Damned if I do, Damned if I don't. Damn it, I will!)
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To: KittenClaws
It is very puzzling. Gravity's force is supposed to be acting on everything with equal force. So why doesn't the bottom move?
8 posted on 10/04/2012 5:01:09 PM PDT by jwsea55
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To: Randy Larsen

I agree. The lower part is being lifted by the collapsing force of the upper part. That is what causes the rotation at the bottom. It is being pulled into the compacted coil.

I had high school physics and I believe it was the most useful course I took in school that helped me in my adult life.


9 posted on 10/04/2012 5:03:41 PM PDT by rw4site (Little men want Big Government!)
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To: jwsea55

My take? A released spring contracts towards the center from both ends. The movement of the spring from the bottom up is being counteracted by the force of gravity down, and so stays stationary. Just a guess.


10 posted on 10/04/2012 5:07:51 PM PDT by Sergio (An object at rest cannot be stopped! - The Evil Midnight Bomber What Bombs at Midnight)
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To: rw4site; Randy Larsen
The lower part is being lifted by the collapsing force...

That's the funny thing. The bottom is going against gravity. All the energy is getting transferred to the compression and rotation.

11 posted on 10/04/2012 5:08:59 PM PDT by jwsea55
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To: jwsea55

Slo-Mo is right, I waited 5 minutes for the video to start......and it never did.


12 posted on 10/04/2012 5:11:08 PM PDT by Hot Tabasco (')
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To: jwsea55

All the energy [one would think is being exerted on the bottom] is getting transferred to the compression and rotation.


13 posted on 10/04/2012 5:11:43 PM PDT by jwsea55
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To: jwsea55
It is very puzzling. Gravity's force is supposed to be acting on everything with equal force. So why doesn't the bottom move?

It IS acting on everything with equal force. But the bottom of the slinky is actually the end of a spring that is compressing while it is being dropped. So the bottom is coming up at the same rate it is dropping, which makes it seem that it isn't moving at all because the forces are being cancelled out - until the top of the spring "catches up" with it, finishes the compression, and the whole thing drops.

The MORONS who made this video spouting off about "gravity messages not reaching the bottom of the spring" are either too stupid to live, or are educational disinformation agents.

Consider - the speed of gravity is FASTER than the speed of light. And this is easily proven. It takes light over eight minutes to reach the earth from the sun, yet the earth follows an exactly curving eliptic gravitational path of constant adjustments every micro-second to follow that ellipse, rather than simply go flying off into space.

So the sun "communicates" it's gravity to earth that fast, but gravity can't manage to "communicate" to the bottom of a slinky?

Like I said, too stupid to live.

14 posted on 10/04/2012 5:13:50 PM PDT by Talisker (One who commands, must obey.)
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To: jwsea55
It is very puzzling. Gravity's force is supposed to be acting on everything with equal force. So why doesn't the bottom move?

I can't remember the time it took in (split) seconds for the top of the slinky to make its way to the bottom without watching the video again, but that seems to be the key.

Slo-mo plays with our minds a bit. The bottom does move, but not until the top reaches a "critical mass" point. The bottom is connected to the top, after all.

The slinky is a whole object, but its mass is "spread out" by design, the physicists discuss this - the same thing happens with a "solid" object (say, a lead bar), just quicker.

Like I said, my math skills are mediocre.

15 posted on 10/04/2012 5:15:38 PM PDT by KittenClaws (You may have to fight a battle more than once in order to win it." - Margaret Thatcher)
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To: Hot Tabasco
Slo-Mo is right, I waited 5 minutes for the video to start......and it never did.

Not sure, I just loaded the page again and played it. No problem. Maybe cached on my machine.

16 posted on 10/04/2012 5:16:57 PM PDT by jwsea55
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To: Randy Larsen

I’ll try my hypothesis...

The downward pull of the stored tension in the slinky plus gravity is exactly the same as the tension of the slinky thus counteracting the pull of gravity. Once the tension+gravity equalizes to the weight of the slinky alone, the slinky falls at the normal rate of 32 ft.per sec./per sec.

I hope that makes this clearer for you.

If not, well you can say I’m full of $hit.

_______________________________________

Thanks, that helped me out a bit.


17 posted on 10/04/2012 5:17:33 PM PDT by KittenClaws (You may have to fight a battle more than once in order to win it." - Margaret Thatcher)
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To: jwsea55
Think of it this way. The bottom has already fallen.
The constant force of gravity can only tension the slinky so much. Since it has already “fallen” as far as it can with gravity there is the opposite tension already loaded in the slinky. Let go of the top and the gravity and tension (being equal) have to catch up to eachother before the bottom will fall.

If you were to stretch the slinky longer than plain gravitational forces the bottom would actually rise before falling because the tension is more than gravity. If you compress the slinky all the way and drop it the whole thing will fall at once.

18 posted on 10/04/2012 5:22:20 PM PDT by Organic Panic
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To: KittenClaws

The red dot on the moving chart is supposed to represent where the center of mass is moving. The blue on the spring represents the compressed part.


19 posted on 10/04/2012 5:24:08 PM PDT by jwsea55
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To: jwsea55

Pretty cool. Definitely gets you to think about the various forces, stored energy, etc. in play, and how they interact with one another as the center of mass of the object falls.


20 posted on 10/04/2012 5:27:56 PM PDT by MCH
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