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There is no cylinder
So suppose you have a very long cylinder of some kind of flexible metal (say 100'). One one end is Point A and on the other is Point B. If you put force on Point A to roll it forward, then Point B also rolls forward but not instantaneously.
Now, what happens if you shorten the cylinder and use a less flexible metal. Say it's just a 4' cylinder of steel with Point A and Point B. And again, you put force on Point A to roll forward. Visually, it appears that Point B moves in conjunction with Point A. But in reality, does it really lag by some very small amount of time?
There is no cylinder
I can't tell if that's a real answer or you being sarcastic. Are you saying that it's just a bunch of atoms and that there isn't really an object? If that's the case, then it seems (and I agree with) that Point B is behind Point A.
Damn...that looks just like your mom when I stick it in her butt
Have you thought about asking her/him if they can feel the difference?
You're talking about your , right?
I don't think anyone should diminish your question.
Wolfram alpha it
that's what I always used to do with that kind of hw in hs and college
Yeah. This obviously was the wrong forum.
Loved physics. I'm IT but better than Math. Remember alot of examples turned out opposite of my initial expectation. Impressed me. Would physics again.
SfS...you know how he's acting? How, Dale?
Dale:::Glad to be alive.
SfS, Bless your heart, boy.
You are correct, it does lag. Or I gather this is what you thought.
This problem involves a cylinder so it makes it more difficult but this is the only way to ask the question you want answered.
So if I could make it easier can we assume this happens with only one external force?, the one you put on the cylinder at a specific point A. This means no gravity and no friction involved because if this happened on the earth both of these forces would be involved and with friction causing the rolling. the question becomes more difficult but you would get the same answer. So if I could rewrite the question as:
You have a long cylinder at rest in space with point A on one end away from the center of mass of the cylinder and point B at the other end of the cylinder. A force is applied at point A and causes acceleration (ie the cylinder starts to move).
Since point A is not at the cylinder's center of mass or along the axis of the center of mass the cylinder would begin to rotate in two ways. A and B would rotate length wise around the center of mass AND the cylinder would also start to revolve around the axis that runs down the center(this is what your question is interested in). Also its center of mass would accelerate (btw the center of mass would not even exist ON this cylinder if it was hollow like a straw.) You are interested in the revolution around the axis down the center of the cylinder it sounds like. So, when a force is applied at A, B would not be Directly affected. It would actually be the bonds between all the atoms between A and B that would cause B to start to rotate (thus accelerate) a bit later. It would almost be like these bonds are springs and you would first load up the springs around A and this would follow down the line to B. So this is sort of a physics and chemistry question. And the physics of bonds is complex so we will stick with the spring analogy.
So if you were able to keep a view down the axis of point A and point B, point B would appear to lag behind in rotation in my estimation.
Now it gets more interesting if we applied this force over a period of time and then stopped applying the force. Would A and B eventually look like they would rotate together sometime after the force was stopped? This gets a bit weird because it would probably be best answered by involving the use of energy ideas and probably resonance and the consequences of bonds stretching reacting to other bond stretching and/or energizing. So the spring analogy is probably useful.
Now we get into conservation laws and resonance and such. I think the following video might help. Would A and B become synchronous in their rotation later on? I think so. Do thus synchrony get disturbed and the reestablish with no more force or energy applied? ie does it go in and out of some resonance... not sure.
This video is where it leads me. These atoms do have elasticity when bonded and energy can be transferred. So take a look:
Play the video and watch how the metronomes (atoms with different states) synchronize. This really is a type of mechanical wave subs uted for an electromagnetic interaction between atoms.
https://sciencedemonstrations.fas.ha...ion-metronomes
So I think you are correct but the question gets funky if the force is taken away as to what happens to point A and B if NO external forces outside the atoms act.
The video is really cool in the above. I wish I had seen this sooner. I like this type of stuff. But sometimes you really have to pare down the question to make it more applicable to a simpler form of physics. And I dont mean to show off and might be wrong, but its still enjoyable for me and maybe you too. Most of the easy mechanics physics questions ask about point masses in simple environments and then move into extended objects like yours. The level of the atom then makes things more difficult and you have to go modern physics.
https://www.youtube.com/watch?v=yVkdfJ9PkRQ
This is also cool. This is where I am coming with what happens after the force is no longer supplied... what happens....
In your example of a cylinder with patterns and dealing with atoms causing other atoms to react might be as simple as the same length of thread pendulums all lined up and bound to each other through the horizontal they hang from. the first one is made to oscillate by a force (merely making it swing) it would cause all the others to swing after time but would they eventually go out of synchrony...
I know this is along way off of SF6 question but its answered I think.
https://www.youtube.com/watch?v=Tlcsym0dC9Y
The above would be simpler if the atoms (pendulums) were all the same length and then point A is forced to oscillate and then let go of. Point B down the line would be behind. Even in atoms. But would they "catch up" ...
Last edited by pgardn; 04-06-2022 at 09:32 PM.
Thanks for taking the time. Yeah...I didn't even consider friction or gravity. And in hindsight, maybe I should have asked the question with Points A, B, and C. With B being in the middle and the point where the force was applied. I think that would negate the differential between the original A and B. I started thinking about rolling up a poster or map where if you only applied force to and end point, you end up with an very imperfect roll. So if you applied force to the exact midpoint, do A and C lag.
Or the other way I guess was to assume a floating cylinder in a vacuum.
That's a very interesting point about stopping the applied force.
I'm going to check out the video and the one below when I get some time. I only took high school physics but I wished I would have taken some in college because it's all pretty interesting to me. For some reason, I think about these things when I try to fall asleep. It's almost like a koan I guess.
Anyway, I appreciate the explanation and links.
Gravity will still act in a vacuum on Earth but I get what you are trying to achieve.
Also, you now got me thinking about just about how we grab objects and move them. Sometimes they bend. I was just helping put up a wire fence with T posts and all and we bent wire around the T posts. The wire changed color a bit a gave off heat when bent, you could feel it. This is the hallmark of a chemical reaction. So these types of things lead me to all sorts of other thoughts so I appreciate an occasional diversion to physical phenomena I have not thought about.
I really dont know enough about the physics of chemical bonds is what it comes down to.
Really changing the subject now but when I was 25 or so, I worked on my uncle's farm/ranch for the summers. He had just bought it and it was just raw land with no improvements. 140 acres that I got to install T posts and fencing around. Plus interior sections. With some barbed wire on certain areas. That was the hardest physical labor I've ever done.
Bend over, I'll give you a very long cylinder...
Loved chemistry, liked biology and nutrition science. Always hated in' physics, though.
Also trigonometry kicked my ass. Those trig proofs scalped me of many brain cells
Algebra and statistics always came naturally to me. geometry of any kind
Man...I loved Geometry. For some reason, it always clicked for me. On the other hand, I hated Algebra, Trig, and Calc. But looking back, it's probably because I half assed it in the beginning and never really caught up. I didn't really care for Statistics but it was never difficult. And in hindsight, it's one of the more important maths one can take for real life applications. Even if one can't do the math part of it, the ideas behind it apply to so many parts of life.
Eeeeeeeyuppers. It is the most important particularly if you want a high paid data analyst type job. Nobody cares if you can do trig or derivatives or integrals or differential equations. If you can find the z-score or the p-value or the t-value and know what alpha is and how to use it in a business context, you ace interviews and get paid.
It's way more useful than just that. Even on everyday decisions (business or otherwise), understanding how to calculate risk (even very simple probabilistic risk) is worth knowing. Even if you're off on your risk assessments, you at least have an idea.
Just knowing what you need for a return (vs your risk) is pretty informative.
ST post of the year 2022 nominee here
Oh yes it’s hard, ESPECIALLY with barbed wire. Double stranded wire without barbs is much, much easier. Putting in the H posts, the wooden post that gives it stability along with just wooden posts can be very difficult, even with an auger on a tractor if the soil is packed.
changing the subject back again that wire can expand and contract a whole lot I’m thinking, so I asked the guys I was doing this with about the tension requirements. We did this fencing in eastern Colorado where you can get 90’s in the summer and -20F in the winter through many seasons. I thought it might snap the wood posts, even the ones in the H posts. They were totally unconcerned so I looked at the other older fencing and it was fine. We used a tractor with a “come along” for the tensioning. It still worries me now but the other guys said “high tensile strength” and I just said “okay” So I still don’t get it. During the winter storm we had a huge telephone pole just snap in the cold. My neighborhood stayed offline for an extra day and a half when the rest of SA had power. Lots of physics/chemistry going on in the above that I’m not sure about.
Anyways, barbed wire is not pulled nearly as tight as other wire cause it will snap. It’s a total pain in the ass.
(Incoming “I’ll show you a …. )
Oh… we also used a gasoline powered T post pounder. Hard to lift but you just let her rip and it pounds them in easily. That also made the job easier.
Last edited by pgardn; 04-08-2022 at 09:34 PM.
This is true for the most part.Only trig I ever came upon was on tests.
In real world, you have all your resources next to you. You don't need to memorize.
But because some phenomena go back and forth repeating themselves, waves, oscillations, etc… it’s super useful in physics and other things that cycle through some pattern. Very important in electricity to astronomy. All from comparing sides from a freaking triangle made by a line moving in a circle. It’s quite amazing to me. I would have never seen this unless I was taught it.
We found out Bin Laden was in a certain location by “shining” lasers on windows of the complex he was in while his voice/ sound waves vibrated the windows in his voice pattern. Thats fckn awesome to me. We read his particular pattern of sound wave frequencies….that goes back to trig functions.
Humans didn't do those trig functions, though. They were all done with state of the art computer assistance.
Heck, FORTRAN, the original math computer language that can do trig and diff equations, has been around since the time of JFK. It's not novelty.
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