Why Do Wet Plates Stick Together?

[zapatos]

Due to my dishwasher being broken, I found myself doing dishes by hand for a few days. We have some Correlle dishes that stack very tightly together, and I noticed that when they were stacked while submerged in water, it was quite difficult to pry them apart. A couple of times I even stuck a knife between them to pry them apart. Similarly I was making split pea soup tonight and after rinsing off the dried peas which all have one very smooth flat surface, I found that they dropped out of the colander in one stuck-together clump.

 

I assume the combination of water with smooth flat surfaces is the reason they are sticking together, but I don't understand what is occurring. Can someone please explain to me the physics of this phenomenon?

[iNow]

Have always thought it's related to hydrogen bonding, but suspect someone better educated / more experienced than me in this space can better clarify.

[studiot]

Try this experiment, next time you are washing up.

 

Submerge a stack of plates in the washing up bowl.

Swirl the washing up mop above the stack creating a whirlpool.

Watch the top plate rise in the whirl up off the stack.

 

I suggest that the plates stick together due to residual material and air trapped between the plates.

The air will be at atmospheric pressure when dunked.

The water will be at slightly higher pressure.

 

This will tend to hold them together like the magdeburg hemispheres.

 

www.google.co.uk/search?q=magdeburg+hemispheres&rlz=1C1AVNG_enGB673GB673&oq=magdeburg+hemispheres&aqs=chrome..69i57.9387j0j8&sourceid=chrome&ie=UTF-8

[swansont]

Stuck while submerged, or stuck after taking them out of the water? If the latter, it's the lack of air between the plates. The water seals the tiny gap, and air can't get in. If air can't get in, any separation of the plates forms a vacuum. External air pressure then keeps them together, which is the Magdeburg hemispheres example studiot linked to above.

[zapatos]

Thanks for the link! I'll submerge clean plates tonight and try to separate them both in and out of water to be sure of my method.

[studiot]

Thanks for the link! I'll submerge clean plates tonight and try to separate them both in and out of water to be sure of my method.

 

I've been hold back the washing up until your update and I've run out of plates that have only been used thrice.

 

 

So please update soon.

 

[zapatos]

 

I've been hold back the washing up until your update and I've run out of plates that have only been used thrice.

 

 

So please update soon.

 

 

 

So sorry! Hope my delay did not cause you any gastrointestinal distress!

 

I swirled the water above a stack of plates and observed the top one quickly rising to the surface once I got the water moving fast enough. Prior to liftoff the entire stack of about five plates started rotating with the water. That was interesting. Did the water movement decrease the pressure on the top plate?

 

I tried clean plates and dirty plates, with and without soap, and put them into the sink singly and as a stack. Generally speaking what I observed was that when the plates nested well (no food particles or irregularities in the plates), they stuck together whether submerged or if I first removed the stack from the sink.

 

When I tried to separate them when submerged I found it was fairly easy to separate with little force if I did so very slowly.

 

Once a stack of plates was removed from the water, the adhesion was noticeably stronger. At one point I lifted two plates by gripping the edge of the top plate only with my fingernails. The bottom plate stuck until I pried it apart.

 

On a separate note, my wife now believes I'm OCD (or a bit of a nerd) for washing clean plates.

[studiot]

 

On a separate note, my wife now believes I'm OCD (or a bit of a nerd) for washing clean plates.

 

Let this be a warning to others

 

[StringJunky]

 

 

So sorry! Hope my delay did not cause you any gastrointestinal distress!

 

I swirled the water above a stack of plates and observed the top one quickly rising to the surface once I got the water moving fast enough. Prior to liftoff the entire stack of about five plates started rotating with the water. That was interesting. Did the water movement decrease the pressure on the top plate?

 

I tried clean plates and dirty plates, with and without soap, and put them into the sink singly and as a stack. Generally speaking what I observed was that when the plates nested well (no food particles or irregularities in the plates), they stuck together whether submerged or if I first removed the stack from the sink.

 

When I tried to separate them when submerged I found it was fairly easy to separate with little force if I did so very slowly.

 

Once a stack of plates was removed from the water, the adhesion was noticeably stronger. At one point I lifted two plates by gripping the edge of the top plate only with my fingernails. The bottom plate stuck until I pried it apart.

 

On a separate note, my wife now believes I'm OCD (or a bit of a nerd) for washing clean plates.

My guess is that it is the same forces that stick the plates in air as the they do underwater;you have to overcome a vacuum, water pressure and atmospheric pressure bearing down on the water surface, which bears on the plates..

Edited September 20, 2016 by StringJunky

[J.C.MacSwell]

My guess is that it is the same forces that stick the plates in air as the they do underwater;you have to overcome a vacuum, water pressure and atmospheric pressure bearing down on the water surface, which bears on the plates..

The slight difference is that when they are out of the water there is a surface tension at the perimeter that is not there when submerged (which prevents the air getting in...not the main force) I have never had any trouble separating when submerged if I pried and just waited, but when out they can really stay stuck using the same technique...better to slide them apart if they are flat enough.

Edited September 21, 2016 by J.C.MacSwell

[studiot]

OK so now you are properly trained in submerged plate whirling we can make the experiment properly scientific.

 

Whirling the water to create a whirlpool obviously somehow exerts an upward force on the plate.

 

Does it make any difference whether you whirl clockwise or anticlockwise?

 

[imatfaal]

OK so now you are properly trained in submerged plate whirling we can make the experiment properly scientific.

 

Whirling the water to create a whirlpool obviously somehow exerts an upward force on the plate.

 

Does it make any difference whether you whirl clockwise or anticlockwise?

 

 

You swirl anticlockwise in the Northern Hemisphere and clockwise in the Southern. Only Joking - I'll get my coat.

[J.C.MacSwell]

 

You swirl anticlockwise in the Northern Hemisphere and clockwise in the Southern. Only Joking - I'll get my coat.

Good point. Just a minor effect but In experiments like these the way the World turns affects all the whirled turns...

 

...I'll get my coat as well...