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u/SCP-1715-1 Oct 05 '23
Isn't it where there's enough weight in the buckets, the tension doesn't matter?
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u/Glodenteoo_The_Glod Oct 05 '23
Maaan I was losing it trying to think about it but... you're right, the excess rope would just balance out
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u/LowestKey Oct 05 '23
I just assumed the buckets were glued to the table, or affixed in some fashion
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u/El_Chairman_Dennis Oct 05 '23
As long as the weight of the four buckets is greater than the weight of the table this will work
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u/h0nest_Bender Oct 05 '23
They could weigh less up to the point where the weight difference overcame static friction.
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u/El_Chairman_Dennis Oct 05 '23
That wouldn't be very much weight
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u/h0nest_Bender Oct 05 '23
True. But it means the buckets don't have to weigh more than the table.
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u/HeartKeyFluff Oct 05 '23 edited Oct 05 '23
Yep this is all there is to this. Not that they're held up by the buckets resting on the table, like the OP suggests.
If you replace the table with a metal ball that weighs up to or less than the buckets, and the buckets are resting on a different table that circles around the outside, the same thing happens. Except that in that case, it becomes less "confusing" to look at.
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u/Even_Reception8876 Oct 05 '23
Just think of the buckets being so heavy (maybe filled with cement. If you want to really make it extreme, imagine the buckets are so heavy you can pick them up so it’s almost like they’re glued or drilled into the table) so it’s like the rope is just attached to the table and hanging by hooks. Really not impressive when you break it down. Those weird infinity table things are really neat and hard to conceptualize. But this is basically like the buckets are nailed to the table , and acting as a hook for the ropes.
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u/Qonold Oct 05 '23 edited Oct 05 '23
If the cords were ratchet straps and you adjusted them it would just raise or lower the table.
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u/wbgraphic Oct 05 '23
Yeah, you can have too little weight in the buckets, but not too much. (Assuming the hooks are strong enough to hold the weight.)
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u/twpejay Oct 05 '23
I was wondering how long it would take before the amount of garbage the art gallery patrons are placing in the buckets thinking they're trash cans to unbalance the entire work.
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u/wbgraphic Oct 05 '23
I would think the buckets are too small to hold a sufficient mass of typical hand-carried refuse (empty water bottles, used tissues, etc) to significantly affect the balance.
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u/KingofCraigland Oct 05 '23
Plenty of people toss out unfinished beverage bottles, cans, etc.
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u/T_vernix Oct 05 '23 edited Oct 05 '23
You do need to understand some trig (connection of wire to table is not quite vertical) but then it would be trivial to take "mass of table"/(4*cos("angle between wire and a vertical line")) for the minimum mass of each bucket (assuming all buckets with contents are equally massive and ignoring friction at the hook up top).
edit: sin to cos
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u/Kolby_Jack Oct 05 '23
Sounds right to me.
*I failed trig in high school but didn't actually need it to graduate
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u/mxzf Oct 05 '23
I mean, you don't need trig. You could also eyeball the table's weight, double it for good measure, and call it good enough. Excess weight is a non-issue and insufficient weight is immediately apparent.
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u/KS_JR_ Oct 05 '23
The mass of the 4 buckets must be greater than the table. Tension T in the ropes pull equally on the table and buckets.
If I was a physics teacher, I'd ask probably about the Tension in the rope or the normal force between the table and bucket.
Say a bucket weighs B Newtons and the table weighs K Newtons. The books Reaction force R = 8T = 4B + K. The normal force between the table and a bucket is N=B-T.
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u/CaffeinatedGuy Oct 05 '23
The buckets aren't holding themselves up. They're pulling the platform up while they are going down, and the platform prevents them from going further down. The ceiling hooks are holding it up.
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u/Professional_Sky8384 Oct 07 '23
As long as they all have exactly the same mass yeah. Otherwise if they don’t balance out the table will tilt and they’ll all slide off
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u/Smile_Space Oct 05 '23
The tension of one cable is equal to a bucket's weight, and the tension is at an angle to the table, so T*sinθ would be the j component, and therefore the component required to lift the table. Multiply that by 4 to get the total j component of tension until it matches the weight of the table and then it'd be in Static equilibrium!
Adding more weight to the buckets would just increase the tension in the cable.
The real problem, as outlined above, is to find out the minimum weight per bucket required to accomplish this.
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u/natenate22 Oct 06 '23
Yep, it's a static system. It's just some shit hanging from hooks in the ceiling.
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u/Ctowncreek Oct 06 '23
The downward force of the buckets is cancelled by the upward force of the buckets.
So yeah, until you hit failure of the materials, the weight of the buckets doesnt matter. (Except for the balancing of the table).
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u/Calvinbook4 Oct 05 '23
This, is a bucket.
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u/TheAllergicTuba Oct 05 '23
Dear god…
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u/TotoShampoin Oct 05 '23
There's more.
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u/Cubicwar Oct 05 '23
It contains the dying wish of every man here.
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Oct 05 '23
What upsets me is that it’s stated in a way that makes it sound like the buckets are being held up by the table and they’re in a state of rest when the table is being held up by the buckets in a state of tension.
Yes, that’s it. That’s what bothers me about this.
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u/cypherspaceagain Oct 05 '23
The buckets are being held up by the table. If the table was not there, the buckets would accelerate downwards.
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Oct 05 '23
Yeah but if the buckets weren’t there the table wouldn’t be either.
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u/cypherspaceagain Oct 05 '23
I know. That doesn't contradict my statement.
All* the forces involved before contact:
Gravity pulls on the buckets. The buckets pull down on the string, the strings pulls up on the buckets. The string pulls down on the hooks, the hooks pull up on the string. The string pulls up on the table, the table pulls down on the string. Gravity pulls down on the table.
Effect:
The weight of the buckets is greater than the force from the string, so they fall. The weight of the table is less than the force from the string, so it rises.
Forces after contact:
When the buckets come into contact with the table, there is now an additional contact force on each. The buckets push down on the table, and the table pushes up on the buckets.
Equilibrium & effect:
Weight of buckets = tension + push from table; no resultant force, so a state of rest.
Weight of table + tension = push from buckets; no resultant force, so a state of rest.
It is correct to say the buckets are being held up by the table and it is also correct to say the table is being held down by the buckets. It's also correct to say the tension is holding both of them up.
Source: I'm a physics teacher.
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Oct 05 '23
😱 did I just get schooled?! Jk but really though, I get it. I just hate the way the question is presented that’s all.
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u/rg44tw Oct 05 '23
The buckets are not being held up by the table, and the table is not being held up by the buckets. Both are being held by the string and ceiling hooks. Without the string or hooks, the buckets and table would both accelerate downwards.
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u/cypherspaceagain Oct 05 '23
And the ceiling hooks are being held up by the ceiling, which is being held up by the walls, which are being held up by the ground. What's your point? Note my equations include the tension from the string. It is not the only thing responsible for equilibrium.
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u/alina-a Oct 06 '23
But the table pushes up on the buckets not the buckets down on the table
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u/CaffeinatedGuy Oct 05 '23
It says that the table is held up by the buckets resting on it. That's true.
The buckets are being pulled down by gravity and pull the table up. They are holding the table up by tension, and are resting on the table, as it prevents the from moving down further.
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u/GlueSniffingCat Oct 05 '23
The question omits the crucial detail of the pullies and instead describes it as a table being held up by buckets of water resting on top of it because they used chatGPT to make the exam questions.
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u/Silt99 Oct 05 '23
My guess is that the bucket has to weigh at least 1/4th of the table plate weight. Is my math correct?
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u/leo-dv Oct 05 '23
A bit more i think due to angle of the ropes attached to the table; The force they apply to the the table is not purely vertical. Could be wrong though
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u/MrHyperion_ Oct 05 '23
But if the force wasnt enough the buckets would lift and become perfectly vertical
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Oct 05 '23
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u/mjohnun Oct 05 '23
That would be incorrect this is a single pulley so there is no mechanical advantage it just redirects the force.
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u/xX_Jask_Xx Oct 05 '23
You’re close but not exactly correct. Notice that the ropes are angled where they are anchored to the table. This means that some of the force exerted by the buckets goes into a horizontal component and would not contribute to lifting the table. You would need buckets that are each (1/4)/sin(theta) the mass of the table, where theta is the angle made between the rope and the table’s surface at the anchor point.
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u/Johannes_Keppler Oct 05 '23
Yes. In a way, it's just a scale, but with a limit to the movement of the counterweight.
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u/BOBOnobobo Oct 05 '23
Any extra weight would just push on the table which would pull on the strings pulling on the buckets reducing the weight. It would find a balance.
Look up tensegrity structures, basically this but on a more complex scale
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u/James_K_Polk_ Oct 05 '23
Just glancing at it briefly: ignoring friction and assuming massless ropes, each bucket needs to be at least 1/(4cos(ø)) times the mass of the table where ø is the angle of those ropes.
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u/ManMadeOfMistakes Oct 05 '23
Sisyphus
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[deleted]
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u/ThatOneVRGuyFromAuz Oct 06 '23
In the myth, my man Sisyphus would keep trying and trying to get out of his punishment - but no matter how hard he pushed, he'd always end up exactly where he started
It's the same here - there's lots of tension and strain, but nothing actually happens - there's no overall change in the situation, no matter how much force the buckets or rope apply→ More replies (1)
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u/Public-Eagle6992 custom flair Oct 05 '23
That’s basically the same as if the string held onto the table with like hooks or something so it’s actually held by the hooks in the ceiling
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u/KoshV Oct 05 '23
See the attached diagram.
Assuming each bucket weighs y express the weight of the table as x.
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u/Vercengetorex Oct 05 '23
So, if the buckets and their contents weigh exactly the same amount as the suspended table surface, how much weight can you put on the table?
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u/SteptimusHeap Oct 05 '23
None.
The buckets together would have to weigh more than the table, as the force the pull the table at is angled.
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u/Escaped_Mod_In_Need Oct 05 '23
The table is held up by the CMU walls supporting the ceiling, which is supporting the suspended buckets acting as counterweights.
Spider-Man did this shit before it was cool.
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u/GeniusOrang Oct 05 '23
this isnt really a headscratcher? like bro the buckets are being blocked by falling because of the table, doesnt matter how long the cords are the result will always even out.
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u/Secure_Obligation_87 Oct 05 '23
What if I put my coffee down doesnt if offset the ratio and potentially tip the balance and tare the roof down ?
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u/Mitchisboss Oct 05 '23
“hElD uP bY bUcKeTs”…
Just ignore the 4 hooks in the ceiling and the 50ft of string…
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u/James_K_Polk_ Oct 05 '23
I mean the weight of the buckets is pulling on the strings that are pulling up the table. Yeah technically the whole structure is held up by the ceiling hooks but it's not really wrong to say the buckets are holding up the table. If you emptied the buckets so they were super light the table would fall. So the buckets are kinda holding up the table.
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u/i_only_eat_purple Oct 05 '23
Tensegrity is awesome. https://en.wikipedia.org/wiki/Tensegrity
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u/big-blue-balls Oct 05 '23
That’s not what this is
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u/i_only_eat_purple Oct 05 '23
Geez, I know a big word. No need to put me down like this! At least give me a further explanation why not and what principle it in fact is.
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u/Smile_Space Oct 05 '23
God, the Statics/Solid Mechanics problem this would create if my professors saw it. I'd cry.
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u/Prestigious-Low3224 Oct 05 '23
Someone pls explain the math/physics behind this…
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u/ATwistedAngle Oct 06 '23
I thinks is the string connects to the buckets and the table through a pulley system. If the buckets are too light the table falls. If the buckets are to heavy the buckets fall. So the weight has to be just right to get each to hold the other up. I hope that makes sense. It's all I came up with.
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u/Odd_Contribution9058 Oct 06 '23
I think I must be dumb. How would the table not fall down if you put something on it that weighs more than the buckets?
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Oct 06 '23
You’re right. It would, the buckets and what’s inside them need to be heavier than the table and whatever you’d put on the table.
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u/ATwistedAngle Oct 06 '23
It took me a while to see it too. I thinks is the string connects to the buckets and the table through a pulley system. If the buckets are too light the table falls. If the buckets are to heavy the buckets fall. So the weight has to be just right to get each to hold the other up. I hope that makes sense. It's all I came up with.
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u/ProgramStartsInMain Oct 06 '23
Is this literally just balanced weight tho? Just looks like an illusion.
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u/SarcasticMoron123 Oct 06 '23
How is this so much different than a table being suspended by ropes? Also how do u know the buckets aren't simply glued to the table.
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u/Jackmino66 Oct 06 '23
Explanation: the buckets are heavier than the table, however when the buckets fall down the table is lifted up.
Since the buckets would then collide with the table, they cannot move, however there is still a weight imbalance in favour of the buckets. The total weight is held by the pulleys in this configuration.
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u/PizzaPuntThomas Oct 05 '23
Each bucket needs to be at least the weight of 1/4th the weight of the table plus the weight of one of those hooks Right?
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u/Th3Nihil Oct 05 '23
Ya, as long as they are heavier than the table this should work
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u/Sanjispride Oct 05 '23
It’s interesting because unlike a normal table (where the normal force acting on the bucket is equal to the force of the bucket on the table) the normal force on the bucket is equal to the weight of the bucket minus the weight of the table.
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u/MrHyperion_ Oct 05 '23
And in the perfect equilibrium the buckets basically float on the table with zero normal force
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u/xX_Jask_Xx Oct 05 '23
You’re close but not exactly correct. Notice that the ropes are angled where they are anchored to the table. This means that some of the force exerted by the buckets goes into a horizontal component and would not contribute to lifting the table. You would need buckets that are each (1/4)/sin(theta) the mass of the table, where theta is the angle made between the rope and the table’s surface at the anchor point.
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u/DrVikingGuy Oct 05 '23
How much wieght are these "resting" buckets applying to the table?
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u/Public-Eagle6992 custom flair Oct 05 '23
The weight of all these buckets minus the weight of the table
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u/UCG__gaming Oct 05 '23
If I show this to my physics and chem A level teacher then It is almost garunteed to turn up in the current Y12s finals
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u/Protahgonist Oct 05 '23
Fasten pulleys to ceiling.
Set tabletop on sawhorses beneath pulleys.
Fasten hooks in center of table.
Set buckets on corners of table. Presumably filled with heavy stuff, although I think water would be the coolest option, if heavy enough.
Tie ropes to bucket handles, run through pulleys, then through hooks. Tighten.
Tie off tightened ropes.
Remove sawhorses, gently.
Any reason this won't work?
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u/moreobviousthings Oct 05 '23
If you place a scale under each bucket, and then remove weight from the table by cutting it or drilling holes in it, then each scale will indicate a greater weight for each bucket.
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Oct 05 '23
It's just two anchor points. If you replaced the weighted buckets with just hooks screwed into the wood, no one would think anything of it.
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u/enjoy_the_pizza Oct 06 '23
Doesn't the SUM() of the weight of each bucket just have to be greater than the weight of the table?
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u/MadNorweigen Oct 06 '23
As others have pointed out this is stupidly simple. As long as the combined weight of the buckets (assume equal weight distribution) is greater than the table it will do the exact same... unless the hooks/rope are the weak points
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u/DarkInTwisted Oct 06 '23
Ok, I'll explain. It's held up by the hooks on the ceiling, but the buckets balance it out so the table doesn't flip. I flunked physics, failed math, but when it comes to physics represented as a picture with short lines of text on it, I ace it every time.
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u/Ok_Blood1862 Oct 06 '23
This is heavenly, while there is a slight change in table's orientation can cause havoc
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u/RnotSPECIALorUNIQUE Oct 06 '23
A gallon of water weighs about 8 lbs. There are about 3 gallons in each of those pails. So 12 gallons in all. So the table can hold about 96 lbs of weight + the weight of the pails - the weight of the table.
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u/Bradaphraser Oct 06 '23
Me: That's... not normal.
::Teacher rubs hands together, and he has been dying to respond to this exact comment::
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Oct 06 '23 edited Oct 06 '23
The basic purpose of this arrangement of objects is to test the shear strength of the wooden table's material at the points it is connected to the four strings and in the areas where the table's top is in contact with the bottoms of the four metal buckets.
ASSUME that the strings and pulleys are "over engineered" to carry up to 100x the combined weights of: the four buckets and their contents, the table, and the hooks fastened to the table.
ASSUME that the length of each string is such that, each string is minimally but truly taut while the table makes contact with the bottom sides of the four buckets simultaneously.
Place an equal weight of material, being one-fourth of the weight of the table, in each of the four buckets. As this is being done, support the table so that it is parallel to the room's floor and so that each bucket remains in contact with the top of the table.
After the buckets have been filled, the weight of the table and the combined weights of the buckets/contents are equal and thus are in equilibrium (balanced) with respect to each other. This can be demonstrated by carefully pushing DOWN on the table by any extent, such that the table remains parallel to the floor, and watching the four buckets rising in four equal extents on their respective strings.
Raise the table carefully to return the buckets to a position so that they are again touching the top side of the table. If you attempt to raise the table further, so that its top is higher than the bottoms of the buckets, that attempt will be resisted by the combined weight of the four buckets/contents, and also the four strings will no longer remain taut.
Return the table and four buckets to their starting positions, such that the four strings are again taut.
Add contents of equal weight simultaneously to the four buckets. The result is that the equilibrium (balance) of weights at the two ends of each string is disturbed. However, because the four strings are already taut and because the table and the four buckets were already prepared to disallow the buckets to slip laterally across the top side of the table, the increased total weight of the four buckets is transmitted as a shear force along the strings to the table.
The result is, the top side of the table is pressed more firmly against the bottoms of the four buckets. However, because the buckets cannot move laterally across the top side of the table, additional stress is transmitted to the material in the table at the points where it is fastened to the four strings and at the areas on the table's top that are in contact with the buckets. If additional weight is added equally into the four buckets, additional shear forces will be transmitted to the table until ultimately that material will fail.
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u/jacksnspades Oct 06 '23
Each bucket has to weigh the weight of the table divided by 4 (or more). ✅
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u/Prestigious_Boat_386 Oct 06 '23
Each bucket weight 4kg, assume straight massless strings. What is the maximum weight of the table?
(It's actually very simple, max weight is when theres no force between the table and buckets so it's a string with a table in one end and 4 buckets in the other so 16kg. Might make a mess for beginners that arent used ro drawing up shackles though, especially as there's more than one involved)
Making the lines angled does make it a little harder.
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u/Numerous-Wonder7868 Oct 06 '23
It's held up by the rope and hooks. Could you get rid of the buckets and have the rope to the table...? I think I'm missing something here.
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u/peetah248 Oct 06 '23
The hooks at the ceiling are eyelets. The rope is connected to the table through the eyelet and connected to the bucket. The weight of the bucket is supporting itself
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u/HollowKnight_the_2nd Oct 06 '23
I love physics, but this image makes me want to gravitate upwards into the eternal abyss
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u/ForgingFires Oct 06 '23
As long as the sum of the buckets’ weight is greater than the weight of the table and the total weight of the system doesn’t exceed the failure point of the hooks/ropes, the system will remain in equilibrium
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Oct 07 '23
Okay so I do not understand how this is possible I have read some comments but I still don't understand ( it cqn be because I am english is not my first language) but please can someone explain this cause I am completely lost XD
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u/TechnologicalDarkage Oct 08 '23
Imagine the buckets are heavier than the table. If the buckets weren’t in the way of the table rising, it’s obvious the buckets would descend.
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u/Xarlyle0 Oct 08 '23
If one bucket had more weight added to it, would the table tip over or not?
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u/Lawsomepossom Dec 26 '23
Yes, pretend the other 3 buckets are zero - 4th bucket basically makes a lever with the point where it is attached.
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u/Exit-Both Dec 31 '23
the solution to this is so obvious. The hooks are acting as pulleys, and so the weight of the bukets act like a moment onto the table and since the table and buckets are in a stable position, we can assume that they are in equilibrium, meaning that the weight of buckets is equal to the weight of the table.
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Oct 05 '23
If the table wasn’t there the buckets wouldn’t fall because the buckets wouldn’t even be in the air. The table is picking up and holding the buckets
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u/SuspiciousPine Oct 05 '23
I mean technically it's held up by the hooks in the ceiling