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Post by reTrEaD on Oct 3, 2023 9:34:54 GMT -5
The rules:- All replies must have any answer contained within a spoiler.
- Failure to comply with rule-1 will result in a brief ban.
- Be honest. If you peak into a spoiler (including the hint) before making your reply just say so.
Now, on with the show...In the video below, the ladders don't remain in sync. Your mission, should you choose to accept it, is to explain why. Hint: It's all about the torque. But what causes the torque and what's the result of the torque?
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Post by newey on Oct 3, 2023 11:29:59 GMT -5
If this were in a vacuum, both would fall aat the same rate. However, here, in air, drag matters. The ladder that is hitting the table starts out experiencing the same drag, but as each rung lands on the table, there are fewer rungs still falling through the air, meaning less drag overall. so the ladder falling all the way has more drag and is slower And, I did not look at the spoiler beforehand. But when I did, it didn't help me any, other than making me think I'm probably wrong. |
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Post by JohnH on Oct 3, 2023 16:46:05 GMT -5
Explanation below.....
Ok so I reckon the key to this is the fact that the rungs are tilted alternately. Were it not for this, with horizontal rungs, the ladders would fall at equal rate because then, there would be no forces transmitted up the wires as a rung impacts the table.
But, with skewed rungs, when one hits at one side it imparts an impulsive force to that rung that causes it to rotate about its mid point. And the other end tries to rotate down. in doing so it sends a tension shock up the cable, giving extra downw;uard impulse to rungs above. This happens alternately left and right, and after several have hit, the effect has imparted enough extra impulsive 'tugs' on the still falling rungs that they have fallen noticeably faster and further
If you'd like to experience this effect personally, take a baseball bat or a cricket bat and strike a fast ball, or a tree, not at the 'sweet spot' but at the very tip of the bat. But not too hard or you may break your wrist!
(No spoilers or hints were viewed, but thanks to my maths teacher Mr Fisher, who explained the physics to me in high school about 45 years ago)
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Post by unreg on Oct 3, 2023 16:48:58 GMT -5
I’m going to guess the logs colliding and bumping into other logs on the table cause B to appear to fall faster, while it’s not falling faster; rather the bumping collision is kind of pulling down on B’s falling rope so it finishes sooner than A.
And how do the logs of B not make any effect on A at the end when B collides with A? I haven’t looked at either of y’all’s spoilers and I’ve not watched the following video that seems to contain the answer; is just my guess. And there’s a question too. |
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Post by reTrEaD on Oct 3, 2023 20:46:19 GMT -5
I’m going to guess the logs colliding and bumping into other logs on the table cause B to appear to fall faster, while it’s not falling faster; rather the bumping collision is kind of pulling down on B’s falling rope so it finishes sooner than A.
And how do the logs of B not make any effect on A at the end when B collides with A? Not sure the the rungs of ladder B ever actually touch the rungs of ladder A. They may be closer to the foreground or to the background than the rungs of A. In any case, I'm absolutely certain there are never any rungs of ladder B touching ladder A prior to the 0:20 mark. And at that point, ladder B has already shifted downward in relation to ladder A.
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Post by unreg on Oct 3, 2023 21:15:37 GMT -5
I’m absolutely certain there are never any rungs of ladder B touching ladder A prior to the 0:20 mark. And at that point, ladder B has already shifted downward in relation to ladder A.
My question had to do with the collision having an absence of effect on ladder A. But, you make a valid point; perhaps ladder B was in front of ladder A.  Though, then ladder A would need to be a tiny bit larger than ladder B; since they both appear the same size. And, if ladder A was actually a tiny bit larger than ladder B, ladder A would be a tiny bit heavier than ladder B. |
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Post by reTrEaD on Oct 4, 2023 10:47:29 GMT -5
My question had to do with the collision having an absence of effect on ladder A. But, you make a valid point; perhaps ladder B was in front of ladder A. Though, then ladder A would need to be a tiny bit larger than ladder B; since they both appear the same size. And, if ladder A was actually a tiny bit larger than ladder B, ladder A would be a tiny bit heavier than ladder B. Ugh. There's much wrong with this, it's difficult to decide where to begin. When a logical chain has a faulty premise, the rest of the chain becomes meaningless. Also, try to be more observant. - When two objects are of identical size, will we be able to discern that one appears to be larger when it is closer to us? In some cases, yes. In other cases, no. If the change in distance is very small in relation to the total distance, they might appear to be the same size, unless there is a way to measure them more accurately than just eyeballing it.
- This experiment was performed by Professor Andy Ruina at Cornell University, not some kid making a video in his garage. It seems likely to me, care was taken to insure the rungs of each ladder were the same diameter and length, then after drilling were weighed to insure they were the same mass. While I can't certify this is true, I believe this is likely.
- I also believe the ladders were arranged such that they were both in the same plane, equidistant from the back wall. Although I can't certify that to be true, either.
- There are other ways for the individual rungs from ladder A that move toward ladder B, to have their end closest to ladder A, be closer or further from the viewer.
- Pay attention to the way the rungs of ladder A pile up on the table. It's somewhat orderly when there are a few, but it becomes increasingly random as each successive rung added to the unstable and unsettled pile.
- The same unpredictable and sometimes multiple collisions that cause some rungs to be pushed toward ladder A, can also cause them to rotate in the horizontal plane.
- Change the settings on the video and view it at quarter speed. You'll notice some of the rungs rotate slightly clockwise if viewed from the top. Others rotate counter-clockwise, particularly some of the last rungs to join the party. And at the very end, I wouldn't call the rotation 'slight'.
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Post by unreg on Oct 4, 2023 17:13:27 GMT -5
My question had to do with the collision having an absence of effect on ladder A. But, you make a valid point; perhaps ladder B was in front of ladder A. Ugh. There's much wrong with this, it's difficult to decide where to begin.
When a logical chain has a faulty premise, the rest of the chain becomes meaningless. Also, try to be more observant. Is the faulty premise made when you suggested the ladders were avoiding collision since one might be in front of the other? But, you make another valid point; the logs of B may have rotated horizontally out of collision with ladder A. Ahh, maybe I misunderstood your in-front-of-the-other statement; maybe you were referring to the horizontal log rotation; that one end was in slightly front of the other ladder. That’s a good point reTrEaD, thank you. Sorry my observation skills did not succeed this time. |
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Though, then ladder A would need to be a tiny bit larger than ladder B; since they both appear the same size. And, if ladder A was actually a tiny bit larger than ladder B, ladder A would be a tiny bit heavier than ladder B.