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
Fascinating. Thanks for posting that.
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.
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?
The closest explanation that I could comprehend in the simplest way, was “external force” on the “center of mass”
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.
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.
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.
That's the funny thing. The bottom is going against gravity. All the energy is getting transferred to the compression and rotation.
Slo-Mo is right, I waited 5 minutes for the video to start......and it never did.
All the energy [one would think is being exerted on the bottom] is getting transferred to the compression and rotation.
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.
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.
Not sure, I just loaded the page again and played it. No problem. Maybe cached on my machine.
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.
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Thanks, that helped me out a bit.
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.
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.
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.
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