Potatoes Stick to Knife Blade

[dcarch]

so a three inch diameter slice of potato stuck to a knife has 14.7 psi pushing on one side, holding it up to the knife.

 

hmmm, 3 inch diameter, = 7+ square inches of area, x 14.7 lbs/sq-in = about 104 pounds of force sticking the potato to the blade.

 

my bet is, put the potato on the floor, cover it with a cutting board, stand a 104 lb cook on the cutting board....

and you'll get mashed potato.

 

something else is responsible.

 

You are absolutely correct about the 104 lbs force requires. I happened to have tried with two flat glass disks with various liquids. Again, there is no mystery about atmospheric pressure, two flat surface with a little liquid inside creates a vacuum when you try to pull them apart.

 

Air pressure demonstrations, without the use of potatoes or even water:

 

https://www.youtube.com/watch?v=8aud79vS_Jw

 

https://www.youtube.com/watch?v=5tG1Zrz1mbI

 

dcarch

Edited November 6, 2014 by dcarch (log)

[AlaMoi]

so why is the potato not squashed to smithereens on the blade?

 

put a slice of potato on a window screen so there is pressure on both sides.

put a 100 lb flat weight on the slice.

what happens?

 

so why does no pressure on the knife side and 14.7 lb/sqin on the other side not squash the potato slice?

[rotuts]

Would you be able to easily pull those two smooth pieces of glass w a little water ( special water, that would not 'boil' in a vaccum   )

 

in outer space ?

 

here are three true Granton Knives, from Granton GB from my collection :

 

 

note the true Granton 'scallop' goes right down to the blade edge.  the top one is a 8.5 "  "Chef Knife"

 

and the edge does not go down as much, as its a Special Order, they have a page or two of knives w/o

 

the G edge, and the 8.5 " was there.  they added the granton cuts "just for me" (   ) at a nominal charge.

 

potatoes stick to this knife, but not as much as they would w/o that edge.  the bottom is a boning knife,

 

as its not as 'wide' ie 'tall' there is much less flat blade left incontact w the potato so they fall right off.

 

its also noted that you 'slice' w these knives rather than 'chop' right down as Ming did in his

 

shilly vid.  he lives not far from me and I see him from time to time walking his dog.

 

Ill have to speak sharply to him about this.  I do like the aero knife for the

 

'reverse tomato cut'  ie drop the tomato on the knife.  Id get one just for that.

 

Its a big shame the Granton knives are not more readily available.  the steel is thin, they are light and take

 

a very sharp EdgePro edge.

 

you can get some boning and slicing knives from third parties on line.

 

but probably not w the Very Classy Red Handles.

 

and they are not that expensive.   I hear that the ones made w a green handle are pretty awful  I dont care for green.

Edited November 6, 2014 by rotuts (log)

[dcarch]

so why is the potato not squashed to smithereens on the blade?

 

put a slice of potato on a window screen so there is pressure on both sides.

put a 100 lb flat weight on the slice.

what happens?

 

so why does no pressure on the knife side and 14.7 lb/sqin on the other side not squash the potato slice?

 

That too is a very interesting question, often asked by many when atmospheric pressure is discussed.

 

The answer is the same as you, a human being, not crushed to nothing, when you are at all times subjected to around 50,000 lbs of air pressure on your skin.

 

dcarch

[rotuts]

" air pressure is All Around You "

[dcarch]

"-----Would you be able to easily pull those two smooth pieces of glass w a little water ( special water, that would not 'boil' in a vaccum    )

 

in outer space ?----"

 

You should be able to. Imagine,  suction cups cannot possibly work in outer space. If you have access to a vacuum machine, get a suction cup to attach to a glass firmly, then draw a vacuum, the suction cup will fall right off.

 

dcarch

[rotuts]

well that a do-able exp in a Chanber Vacuum Sealer !

 

who is the first to report ?

[gfweb]

A chamber vac would evaporate the water which is gluing the sheets together.  I don't think that a suction cup in a vacuum is a good model for what we are discussing because it fails to account for the water between the panes.

Edited November 6, 2014 by gfweb (log)

[daveb]

Damn.  Is ths topic like a New Yorker cartoon where everybody gets it but me?  Or have you y'all just turned it into a soup sandwich?

[rotuts]

Dammnnn !

 

I know nothing about a Soup Sandwich !

 

Pleaseeeeeeeeeeeeeeeeeee

 

start a topic !!!!!

[Norm Matthews]

I bet a potato would still stick to a knife in a vacuum. 

[dcarch]

I bet a potato would still stick to a knife in a vacuum. 

 

Absolutely. If you take a piece of wet tissue, it will stick on a flat surface without falling. That is the weak force of surface tension of water acting to keep the wet tissue sticking. It takes not much force to peel the tissue off, however. Now try the same size suction cup, you will be peeling against atmospheric pressure.

 

dcarch

[GlorifiedRice]

Its a Seinfeld episode

[TicTac]

Lube your knife with some Olive Oil

Edited November 6, 2014 by TicTac (log)

[AlaMoi]

so air presure is all around us and all around everything and there's equal pressure on both sides and in the middle I assume.

 

so what's with air pressure making it stick to the knife?

 

one can't have it both ways - either there is air pressure on both sides and in betweeen or there isn't.

 

one may not insist air pressure is making the potato slice stick to the knife and also insist there is atmospheric air pressure on both sides.

 

so which is it?

[GlorifiedRice]

Poh tay toh

Pah tah toh

Lets call the whole thing off!

[btbyrd]

[dcarch]

so air presure is all around us and all around everything and there's equal pressure on both sides and in the middle I assume.

 

so what's with air pressure making it stick to the knife?

 

one can't have it both ways - either there is air pressure on both sides and in betweeen or there isn't.

 

one may not insist air pressure is making the potato slice stick to the knife and also insist there is atmospheric air pressure on both sides.

 

so which is it?

 

Believe it or not, those are very important and legitimate questions.

 

14 lbs/in sq (rounded off) is universal, everywhere, it will not do anything until you try to work against it. As I said, there is 50,000 lbs of pressure on you body all the time, however, in the science of fluid dynamics, the pressure is also in you body to equalize the outside pressure. (you will literally explode if you are in outer space)

 

When the food is sticking on your knife, the pressure on the food is the same as the pressure inside the food pushing out, until you try to pull the food away then you will be creating a vacuum between the blade and food and you will have to overcome the 14 lbs/sq in pressure.

 

dcarch

[dcarch]

Its a Seinfeld episode

 

Yes, it is funny how knife makers can profit millions $$$ from selling useless anti-stick knives to the public.

 

dcarch

[scubadoo97]

Don't know if it's been mentioned but a convex edge will reduce adhesions

[AlaMoi]

"until you try to pull the food away then you will be creating a vacuum between the blade and food"

 

so what make the formation of a vacuum so difficult on a flexible slice of potato?

 

a big slice than hangs half-way over the width of a knife sticks - one can pull on the swinging-in-space part of the slice and it still does not want to peel away.

[rotuts]

for a wet potato Im going w adhesion.

 

'dry' veg dont stick, same diameter.  all that atm's would be all over the dry and the wet.

[GlorifiedRice]

Yes, it is funny how knife makers can profit millions $$$ from selling useless anti-stick knives to the public.

 

dcarch

Dcarch the Aero Knife actually has been around for years, My dad bought my mom one in the 80s. They are called cheese knives

 

http://www.amazon.com/Messermeister-Pro-Touch-6-Inch-Cheese-Tomato/dp/B000FJOVTW/ref=sr_1_37?ie=UTF8&qid=1415375414&sr=8-37&keywords=cheese+knives

[Edward J]

Rotus, that doesn't explain why spuds stick to a granton or kullenschliff blade, which is a blade with a series of dimples or grooves on the surface of the blade.

 

Ahhh! But why does a spud stick so tenaciously and other fruit or veg not so?  The fruit or veg can be the same size, same water conten as a spud, but it won't stick as badly as spuds.

 

It must have something to do with van der waals forces and climbing up buildings with suction cups and two sheets of glass with water trapped in between.  Mind you, although a knife (albeit with a convex edge) can be considered hard, rigid and flat like glass, all fruits, veg, and meat are soft, floppy, and--more importantly, porous.

 

I dunno, why does brie cheese stick to a knife? Just because it's a gooey, sticky hunk of cheese is no proper explanation.  As dcarch pointed out, potato starch that hasn't been cooked is not an adhesitive, so in that case, cheese is not an adhesitive either.

 

So, when you encounter the problem of spuds sticking to knives, do what cooks have been doing for centuries now:  You rinse the knife off with water after every 4 or 5 slices.  Voodoo magic, I know, not very scientific, and besides, rinsing washes off that white, starchy sticky substance on the knife blade that only spuds leave behind.  But I can't find an explanation for this procedure other than it works. 

[btbyrd]

As dcarch pointed out, potato starch that hasn't been cooked is not an adhesitive, so in that case, cheese is not an adhesitive either.

 

.... rinsing washes off that white, starchy sticky substance on the knife blade that only spuds leave behind. But I can't find an explanation for this procedure other than it works.

 

 

Check your premises.

Edited November 7, 2014 by btbyrd (log)