Potatoes Stick to Knife Blade

[dcarch]

" a way to prevent air from leaking into the space between the two surfaces "

 

yes again.  if the two 'vacuum' spheres never had the air pumped out, and were 'super welded' together

 

and no air could ever enter the sphere, they would never come apart, so the second statement simply serves itself.

 

Imagine a bellow/accordion with infinitely flexible folds that you can stretch without force, now you cap  both ends to make it air tight. You will experience ATM when you are trying to stretch this bellow. 

 

dcarch

[rotuts]

""  stretch without force ""

 

I know of nothing like this.   'stretch' implies a force applied over a distance, ie work.

 

imagine a finer and finer needle probe places into the section cup, the 'sealed container ' where some air had been pumped out

 

you then measure the 'pressure' in those semi-voids  they would be at less than 1 ATM when an external force was

 

applied to them to 'pull them apart'  at rest, w no pulling force ?  hard to say.

 

between the Potato's cut surface and the smooth knife :  that's the measurement that needs to be made.

 

if the measurement was 1 ATM, then its the water's 'properties' that keep that potato stuck up to the knife.

 

it the measurement is < 1 ATM, then its the atmospheric pressure 'glue-ing' the potato to the knife.

Edited November 10, 2014 by rotuts (log)

[dcarch]

""  stretch without force ""

I know of nothing like this.   'stretch' implies a force applied over a distance, ie work."

 

Yes, it is absolutely possible to stretch an imaginary infinitely flexible bellow without using force. 

I don't remember which Newton's Law of motion/force. If you keep the rate of movement constant, there will be no force required, any resistant then can be attributed to ATM.

 

​Force will be require for acceleration and deceleration for a given mass, but not for a constant speed object in motion against a vertical force. 

 

dcarch

Edited November 10, 2014 by dcarch (log)

[rotuts]

""   stretch an imaginary  """

 

well, perhaps your imagination can, mine cant  

 

but I like the idea.   " More Methode Rotut's " he said 

 

then anything is possible ....

 

 Id say that bellow was an imaginary stretch. ...

 

In the Land of Newton, and M.R.   

 

your example just serves itself by setting up rules that have no real place in our day to day Potato Cutting World

 

but I do support the fantastic idea of thought experiments like this.

 

""  Its the Water ""  and the properties of water that seal the potato to the knife preventing as you say, air entering between

 

the potato and the knife.  a small amount of 'work' Force x distance  breaks this 'seal' and the potato falls off

 

as the potato slice is flexible, the seal migrates down the blade until it falls off completely.

[dcarch]

"---your example just serves itself by setting up rules that have no real place in our day to day Potato Cutting World--"

 

Perhaps. But It is perfectly acceptable in postulating. For instance, will you accept the following imaginary world?

 

Imagine you have a bike with bearings that give you friction-less ride. and you are wearing pressurized space suit, will you accept that you can go on forever on the face of airless moon, once you get going? As a matter of fact, you can even go up hill and down hill without using force, if you apply the law of potential energy.

 

dcarch

[rotuts]

well, what would be for Lunch ?  what about Moon Grit, and my tires ?

 

what if I get hit by a meteor or  such ?

 

I think it would take a lot of work using current ( imaginary ? ) moon suit technology to get up a real Head of Steam

 

so the hills have to be mighty short.

 

any In'N'Out burger stands there yet ?

 

Imaginary Potato Chips ?

 

the potato on the knife is in equilibrium on that knife and adhesion mostly water, maybe a bit of starch keeps it there

 

until other forces  get involved.  the vacuum exp simply confirms these curves :

 

https://www.google.com/search?q=triple+point+curve+of+water&client=firefox-a&hs=zzc&rls=org.mozilla:en-US:official&channel=sb&tbm=isch&imgil=1MdpDtQM29-zGM%253A%253BxCIDVyCN-GYenM%253Bhttp%25253A%25252F%25252Fwww.chemguide.co.uk%25252Fphysical%25252Fphaseeqia%25252Fphasediags.html&source=iu&pf=m&fir=1MdpDtQM29-zGM%253A%252CxCIDVyCN-GYenM%252C_&usg=__DAHwJ6sPRRFxN98PdMm81AggPrc%3D&biw=973&bih=862&dpr=1.2&ved=0CCwQyjc&ei=ayNhVLbxKoqNyASerIHwCQ#facrc=_&imgdii=_&imgrc=1MdpDtQM29-zGM%253A%3BxCIDVyCN-GYenM%3Bhttp%253A%252F%252Fwww.chemguide.co.uk%252Fphysical%252Fphaseeqia%252Fpdh2o2.gif%3Bhttp%253A%252F%252Fwww.chemguide.co.uk%252Fphysical%252Fphaseeqia%252Fphasediags.html%3B391%3B294

 

at some point when you lower the atmospheric pressure the entire closed system,  of water at room temp. and the chamber, water  vapor is produced and it is at a slightly higher higher pressure than the 

 

over all chamber. Potato Falleth.

Edited November 10, 2014 by rotuts (log)

[NEPolarbear]

"Sticky potatoes stick to knives."

 

Will post the link to this MIT study at a later time.

[rotuts]

NEBP

 

now your are talking

 

MIT is not that far from me

 

look forward to what the " TECH" says about this ..........

 

no In'N'Out burgers near there   so sad.

 

but killer fellafels !

[pbear]

Out of curiosity, I decided to replicate Jo's experiment in a way which eliminated the evaporation issue.  To which purpose, I chilled for several hours a potato, a couple of nonstick loaf pans (this one) and the lid for my pullman pan.  I chose loaf pans over knives because I wanted vertical surfaces in addition to a horizontal one.  As for the potato, I wanted uniform slices, so I peeled and sliced 5 mm thick with an electric slicer.  Further, reflecting that vibration might be a cause of the potatoes releasing, I put a hot pad under the loaf pan when doing each run inside the chamber.  And, I ran each test in duplicate outside the chamber, putting the loaf pan on the lid but without the hot pad (figuring the lid already is somewhat dampened and preferring to skew the conditions against dcarch's hypothesis to the extent I could).  Ran each test three times.  Each lasted 28 seconds. 

 

What I found was that the slices on the horizontal surface always fell under vacuum.  Far from the water evaporating, there was always a film of it on the pan sufficient to make the potatoes stick again.  I ran the same potatoes on top of the lid and they didn't fall, except once in three trials one piece (of six) fell, which I suspect means it wasn't stuck on well in the first place.  Moving on to vertical, I used the outside surface of the loaf pan, so slanted slightly in favor of a fall due to gravity.  Interestingly, although the slices under vacuum always slid down the pan, only about a third of them in each run actually fell off.  On the other hand, the slices not under vacuum never moved at all (even with vibration).  From which I infer water tension is indeed a factor, but only a small one.  Mostly, this is about air pressure.

[dcarch]

Good experiment pbear. 

 

Frankly I am very puzzled why it is so difficult to explain atmospheric pressure and two closely attached surface. May be i am not a good ex plainer, but I thought the examples in the videos definitely explained it well. I guess not.

 

I am also puzzled why Rotuts only picked the "swing" example in the link he gave to dispute, but totally ignored the example (copied below) in that link right above the "swing" example, which completely explained why it has nothing to do with water elasticity or potato starch when two surfaces are closely attached.

 

dcarch

 

"What to look for:

The demonstrator will bring out a small stool and a soft-rubber baseball base from a play ground with a handle in it. He will place the base on the top of the stool, and lift up on the handle and the stool will be lifted off the floor easily. He will then show that the base is not glued to the stool by lifting the corner of the base and the stool will fall to the floor.

 

How it happens:

The stool and the base are smooth and will seal out any atmosphere from getting between them. When the demonstrator lifts on the handle, there is a small cavity formed because of the flexibility of the rubber base. There is very low pressure in this cavity, thus allowing the greater pressure of the atmosphere to push the rubber base and the top of the stool together hard enough to lift the stool from the floor.

When the demonstrator lifts the corner of the rubber base, he allows air between the stool and base, equalizing the pressure with the atmosphere, and the cavity is no longer a low pressure area."

[Edward J]

Not a great example, since the news paper doesn't keep air out well.

There are videos in this thread that show how strong the vacuum can be with no water on a simple plastic bag.

If the potato starch and water was so sticky, you wouldn't be able to slide it sideways

 

Great example, since most fruits and vegetables also are porous and don't keep out air well.

 

Regardless of potato starch and water being sticky, you can still slice a spud, horizontally or vertically, I must have sliced close to 25,000 lbs in my career.  It's just that the slices will cling tenaciously to the knife blade as you slice..... 

[NEPolarbear]

Found this in the MIT archives concerning the various potato / knife theories.

 

https://www.dropbox.com/s/vduipe8pxp9ve9w/MIT%20Spud.Knife%20Theory.MOV?dl=0

 

Apparently the potato will not stick when proper vacum is applied.

[rotuts]

the question then is :  how much of a vacuum is being applied ?

 

if it were just slightly less than 1 atm than that would support the 'dueling ATM' theory

 

ie one side would be 0.9999 ATM  ( by the vacuum ) which is less than 1 ATM

 

if it were 'a bit more' than that, it would suggest water is doing something and that something would have to be

 

over come.

 

Adhesion Marches In.

[dcarch]

the question then is :  how much of a vacuum is being applied ?

 

if it were just slightly less than 1 atm than that would support the 'dueling ATM' theory

 

ie one side would be 0.9999 ATM  ( by the vacuum ) which is less than 1 ATM

 

if it were 'a bit more' than that, it would suggest water is doing something and that something would have to be

 

over come.

 

Adhesion Marches In.

 

I don't see the reasoning.

 

There are so many other experiments to show 14.7 lbs/sq. in. of force without vacuum, any water or potato starch involved.

 

As I said, if you have to climb up outside of a skyscraper, you better use suction cups, not cut potatoes.

 

dcarch

[Edward J]

 

As I said, if you have to climb up outside of a skyscraper, you better use suction cups, not cut potatoes.

 

dcarch

 

 

Now we're getting to the meat in the sandwich.....

 

Who really cares about suction cups and climbing up buildings with potatoes tied to your feet?

 

The spuds are sticking to the knife, it's irritating, time consuming, and can be dangerous. 

 

Do you, Dcarch, have advice on how to mitigate this?

[rotuts]

note the three Granton knives in the pic I posted above

 

the blade that's the narrowest works best   no sticking

 

maybe they might make a Potato knife that had the scalloping going up the entire width of the blade

[JoNorvelleWalker]

Now we're getting to the meat in the sandwich.....

 

Who really cares about suction cups and climbing up buildings with potatoes tied to your feet?

 

The spuds are sticking to the knife, it's irritating, time consuming, and can be dangerous. 

 

Do you, Dcarch, have advice on how to mitigate this?

 

I'm not dcarch, however as I indicated in post #84 (though unhelpfully botching the name of the knife brand) in making my gratin dauphinois the other night not one potato slice stuck to the newwest chef's knife:

 

http://www.newwestknifeworks.com/product/kitchen-knives--fusionwood-20-line/9-chef-knife-fusionwood-20/3556

[gfweb]

Oil the knife blade and the potatoes don't stick.

 

Same air pressure, just no water effect.

 

Q.E.D.

[rotuts]

"" Its 

[rotuts]

"" Its the Water ""

[dcarch]

"" Its the Water ""

 

Confirmation bias?

 

dcarch

[Edward J]

I'm not dcarch, however as I indicated in post #84 (though unhelpfully botching the name of the knife brand) in making my gratin dauphinois the other night not one potato slice stuck to the newwest chef's knife:

 

http://www.newwestknifeworks.com/product/kitchen-knives--fusionwood-20-line/9-chef-knife-fusionwood-20/3556

 

 

Thank you.  This is your personal experience/observation, and I respect it for what it is-- a personal experience/observation.  It is also a viable option to mitigate potato slices sticking to a knife blade, and one used by countless people.

 

I also respect gfweb's observation/experience, even though I wouldn't use it.  But again, it is a viable option, and one that is used by countless people .

 

Going over the 5 (five) pages of this thread, I fail to find any personal observations or experiences from dcarch.  I don't know why this is, but we have a lot of science, climbing up walls with suction cups, sheets of glass, and yet, no personal observations or experience concerning slicing a lowly spud.

 

The "test" is very easy, it is not time consuming, does not require expensive equipment or elaborate set ups, nor does it require extensive training.  It (cutting a simple spud) is also very cheap--I bought potatoes the other day for 69 cents /lb, and after "testing", you can cook and eat the spuds.

[dcarch]

------ The spuds are sticking to the knife, it's irritating, time consuming, and can be dangerous. 

 

Do you, Dcarch, have advice on how to mitigate this?

 

I am not sure there is a way, not a single way.

 

Atmospheric pressure is known for centuries. It's effects are well documented. It is everywhere, and it effects everything.  

 

Potatoes, other vegetables, and foods are all different in stiffness, surface texture, and surface area.  Temperature, your cutting habits and different knives, etc. The combinations and permutations are endless. 

 

That said, regarding the OP's question, I do have a couple of ideas.

 

1.  Granton knives can work sometimes for some potatoes, not all the situations. Dimples can help and can also e a problem. They can release pressure as well as act exactly like a suction cup.

 

2. Single bevel less acute edge angle knife is very good to allow the slices to peel away.

 

3. Try cutting under dripping water.

 

4. Try a knife that has thick blade and narrow width.

 

When I get a chance, I will post a picture of a knife I use which basically eliminate sticking.

 

dcarch

[JoNorvelleWalker]

Has anyone tried using a usuba for slicing potatoes?

[daveb]

Yes and no it's not well suited for the task.  Usaba is used for in-hand work, (peeling, can be used for supremes)  and some precise but light duty board work.  The blade needs to kiss the board, not whack it.   Typical slicing and chopping is not what the blade is made for.  Peel, needle (or ken) cut,  (I use mine for micro dice) are where it excells.

 

I can think of no reason to use a single bevel knife (dscrach aside) for slicing tasks on vegs.  Double bevels are stronger at the edge and are better suited.