Physics, or sorcery?


#1

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#2

Without analyzing the statics of it, I suppose the friction of the lines in the hooks at the top plays an important part. But however the statics actually work, it’s a cute concept piece.


#3

The illusion depends upon the assumption that the buckets are actually resting upon the table, rather than merely being balanced in the same place. If, through the pulleys, the weight of all of the buckets is balanced with the weight of the table, they should just stay where they are.


#4

It becomes easier to understand once you realize that the table is being held down by the weight of the buckets. If the buckets were hanging over the edge of the table then it’s easy to see that the table would rise up in the air till it hit the ceiling or the buckets hit the floor.

For this to work the weight of the buckets must exceed the weight of the table, or the table would just fall to the ground and the buckets would be hauled up into the air.

The last thing then is why the buckets don’t go down - that’s because they’re being held by the length of the rope. They want to fall, but that would require the table to rise, and it’s being held down. The clever bit here is that four buckets at the four corners prevents the table from just tilting like it ‘wants’ to do to let the buckets slide off.

If you made the ropes a foot longer then everything would be half a foot lower (half because the ropes are doubled over). And nothing changes if you make the buckets lighter or heavier as long as a) nothing breaks from the stress, b) the buckets are heavier than the table.


#5

Imagine stepping on the table, then getting off. Really, imagine it. Spoiler below.

It goes down, pails go up. You get off. Pails go down, table goes up, until thunk the pails are on the table. Then it stops. You believe that? Does that make this static system more intuitive?

In particular friction at the top is immaterial.


#6

If the ropes are longer then the table will be lower. If they’re shorter then the table will be higher. If the ropes to the buckets are at different lengths then it will not be flat.

The weight of the buckets must be equal to or greater than the weight of the table or the table will fall to the floor, lifting the buckets the equivalent distance.


#7

Suppose, for a moment, that there are two inches between the buckets and the table.

If the buckets are lighter than the table, the table will fall, and eventually hit the ground. If the buckets are heavier than the table the table will rise, and eventually hit the buckets.


#8

Longer ropes, table closer to the ground. Shorter, closer to the ceiling. If the buckets become too light the weight of the table will drag it to the ground and the buckets will be pulled up.

It’s a neat visual piece but if you stop and think about it its just a pulley system but the table is preventing the buckets from dropping to the floor.


#9

Pulleys, how the fuck do they work?


#10

People are correct that the buckets must weigh >= than the table for the system to be stable but if you just had both ends of each rope attached to the table then it would make more sense to see how something can just hang, like a picture or whatever, as long as the forces on each end of the ropes are balanced.


#11

angle = arccos(1/4*(m_table/m_bucket))


#12

It’s also entirely possible for the buckets not to touch the table and have it not fall, but then the table would need to be as heavy as the collective weight of the buckets. At least my intuition tells me so. This would be a fun experiment to do in a physics or science class.


#13

Make the ropes a little longer and everything will hang a little lower.

Making the buckets heavier won’t change anything. They can’t pass through the table. Unless you exceed the ropes’ capacity.

Make the buckets too light and the table will fall to the floor while the buckets dangle loosely.

Move the buckets off the sides of the table and they’ll hang down to the floor while lifting the table up closer to the ceiling.


#14

Many people have eluded to it, but not said it directly:

The buckets are not holding up the table, the ceiling is.

The buckets are pushing down on the table, tightening the ropes. The ceiling is resisting the downward force. If the the buckets were positioned off the table, the weights would have to be equal. Here, the buckets just need to be heavier than the table and the ropes have to be strong enough to hold it all.


#15

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#16

Perfect time for a force balance equation on the table.

Downwards force = table. The buckets are not exterting a downwards force on the table.
Upwards force = force of the buckets.

The weight of the table and the buckets is the same. You could push the table down and the buckets would dangle.


#17

It’s also entirely possible for the buckets not to touch the table and
have it not fall, but then the table would need to be as heavy as the
collective weight of the buckets. At least my intuition tells me so.

That’s correct - if the buckets were equal in weight to the table to within the break friction of the pulleys (very low, so this would be tough) then the table could dangle freely below the also freely dangling buckets.

But it wouldn’t be nearly as stable a configuration, obviously, and the table would hang at an unattractive wobble angle (since middle of the table is the worst possible position for keeping it level) unless you moved the table anchors to the corners and the buckets were all equivalent weight to each other as well. Since it has pulleys, so low friction, I suspect that just a change in humidity from one day to the next might be enough to mess it up.

Also it wouldn’t look as initially mind blowing.


#18

Imagine that each bucket is attached to both ends of the rope (no table.) Each bucket is held up equally by the two rope halves.

Now imagine that the bucket has a piece of table under it, held up on either side of the bucket by a split end of the rope. Same thing: the bucket’s weight is split between the two parts of the rope, and the table segment is held up by one of them. Bucket rests on table segment as long as the table segment is no heavier than the bucket.

Now put the table segments together and attach the ropes to a point in the center. You don’t need to split the table end of the rope any more because the balance is handled by having multiple buckets and ropes.

All simple if you take it in steps.


#19

This is an artwork by Michael Craig-Martin. The buckets are filled with water. So in theory eventually after evaporation the table top will fall and the buckets will fly up in the air.


#20

I always find the reactions to things like these interesting.

At initial first glance it looks wrong, but apply any thinking at all towards the forces being applied and it cannot do anything but make sense…

After that, i realise that a lot of people simply do not really understand mechanical forces/gravity.
I bet there are other subjects where that applies to me though :slight_smile: