A straw through a potatoe, how does it work?

paul.fr · « **on:** 11/09/2007 08:34:10 »

Most of us will have done this at some point. grap a straw and a potatoe, quickly stab the potatoe (apple, tomatoe...) with the straw and it goes through the potatoe. But why and how does this happen? Why does the straw not just bend on impact?

DoctorBeaver · « **Reply #1 on:** 11/09/2007 09:02:36 »

I must have had a deprived childhood. I've never seen that. [

]

syhprum · « **Reply #2 on:** 11/09/2007 09:23:24 »

Straw is composed of pretty tough structural materiel rather like fibre glass also the area in contact with the potato is small hence the pressure is high.
I have not tried this but I do not find it surprising

DoctorBeaver · « **Reply #3 on:** 11/09/2007 11:43:46 »

I bet it wouldn't work with my ex-wife's roast potatoes.

neilep · « **Reply #4 on:** 11/09/2007 13:21:15 »

I've never tried that too.....as a firm believer..etc etc ..la dee dah dee dah !...I will try this......Prsumably it's plastic straws that are the way to go here ?.......well, I suppose I could use a paper straw with a metal BBQ skewer slipped inside !!

lightarrow · « **Reply #5 on:** 11/09/2007 15:43:49 »

Quote from: paul.fr on 11/09/2007 08:34:10

Most of us will have done this at some point. grap a straw and a potatoe, quickly stab the potatoe (apple, tomatoe...) with the straw and it goes through the potatoe. But why and how does this happen? Why does the straw not just bend on impact?

You forgot to say that you have to close the other end of the straw with your thumb. If you don't close it, the straw will deform badly without doing anything to the potato. That is the amazing part of the experiment!

My interpretation (I'm not sure) is this: closing the straw creates a pressure inside of it (as soon as a little piece of potato penetrate through it), so the straw cannot deform towards the inner; on the other hand, the straw's resistance to deforme in the opposite direction, that is enlarging its diametre, is quite high, so the result is that it cannot deform and so it penetrates into the potato as if it was a solid piece of plastic, instead of a thin pipe.

It's really amazing.

paul.fr · « **Reply #6 on:** 11/09/2007 16:06:57 »

Quote from: lightarrow on 11/09/2007 15:43:49

You forgot to say that you have to close the other end of the straw with your thumb. If you don't close it, the straw will deform badly without doing anything to the potato. That is the amazing part of the experiment!

Dearest Lightarrow. I am prepared to be shot down in flames and go to hell for eternity, but i have to disagree. You do not need to put your thumb over the end of the straw for it to work, if you did then the simple answer would be airpressure.

I have done this many times, even this morning with some old apples. And i never put my thumb over the end of the straw, yet it still works. I was always told about it being air pressure, but seeing as it works without the thumb on the end it surely can not be.

But you are right when you say it is amazing, as it is. I may get Anastasia to do this at the weekend and post a video on youtube, to show it without the thumb on the end.

Looks up to the sky for impending thunderbolt.

lightarrow · « **Reply #7 on:** 11/09/2007 16:19:40 »

Quote from: paul.fr on 11/09/2007 16:06:57

Quote from: lightarrow on 11/09/2007 15:43:49

You forgot to say that you have to close the other end of the straw with your thumb. If you don't close it, the straw will deform badly without doing anything to the potato. That is the amazing part of the experiment!

Dearest Lightarrow. I am prepared to be shot down in flames and go to hell for eternity, but i have to disagree. You do not need to put your thumb over the end of the straw for it to work, if you did then the simple answer would be airpressure.

I have done this many times, even this morning with some old apples. And i never put my thumb over the end of the straw, yet it still works. I was always told about it being air pressure, but seeing as it works without the thumb on the end it surely can not be.

But you are right when you say it is amazing, as it is. I may get Anastasia to do this at the weekend and post a video on youtube, to show it without the thumb on the end.

Looks up to the sky for impending thunderbolt.

You mean that it worked that way with non-cooked potatoes? You must have soft potatoes, or hard straws! [

]Apart from joking, I tried several times, with straws 6-7 mm in diametre for drinking coca-cola and non-cooked potatoes; closing the end with the thumb I could perforate the entire potato; non closing it I could only have a deformed straw.
So the experiment must depend critically on the exact kind of straw and potatos. [?]

paul.fr · « **Reply #8 on:** 11/09/2007 16:25:49 »

Non cooked potatoes and standard drinking straws, and it worked! It could depend on the straw and potatoes, i suppose/guess. Now green apples are really hard to get the srtaw through, hold on i have some juicy red apples......goes off to find a fresh straw....

syhprum · « **Reply #9 on:** 12/09/2007 16:09:04 »

I think you are meant to do it with genuine vegetable straws, I think these if you pick a good specimen are sharper and tougher than plastic

Karen W. · « **Reply #10 on:** 12/09/2007 16:21:54 »

We have always used a plastic drinking straw! What is a natural vegetable straw?

I like Alberto have had the same problem with the straw if the top hole was not covered. My straw gets all mangled LOL.. Am I holding it wrong??? Now I am curious as to why I cannot penetrate the potato without covering the end. We have done this many times as I grew up as well as with the children at school.. I am baffled.. I want to learn the new way too!

paul.fr · « **Reply #11 on:** 12/09/2007 16:34:41 »

Quote from: Karen W. on 12/09/2007 16:21:54

We have always used a plastic drinking straw! What is a natural vegetable straw?

I like Alberto have had the same problem with the straw if the top hole was not covered. My straw gets all mangled LOL.. Am I holding it wrong??? Now I am curious as to why I cannot penetrate the potato without covering the end. We have done this many times as I grew up as well as with the children at school.. I am baffled.. I want to learn the new way too!

It should always be done without the thumb, the thumb is just there because it make the "answer" of air pressure easy to understand. you do not need the thumb.

Karen W. · « **Reply #12 on:** 12/09/2007 16:54:52 »

How do you hold the straw? Around the middle?

paul.fr · « **Reply #13 on:** 12/09/2007 17:12:10 »

Quote from: Karen W. on 12/09/2007 16:54:52

How do you hold the straw? Around the middle?

or near the end. just like you would a knife stabbing at a ....something

lightarrow · « **Reply #14 on:** 12/09/2007 17:47:43 »

Quote from: paul.fr on 12/09/2007 17:12:10

Quote from: Karen W. on 12/09/2007 16:54:52
How do you hold the straw? Around the middle?

or near the end. just like you would a knife stabbing at a ....something

...and you, obviously, don't squeeze the straw at all, in doing it, isnt'it?

Cujef · « **Reply #15 on:** 13/09/2007 19:27:28 »

If you take a straw and hit most any object that is somewhat soft, or not completely solid, you can the straw to go into it. The idea is that you will be hitting the object at the correct angle that the straw itself will be perfectly aligned to be incredibly strong. If you hit it at an angle other than exactly straight the straw will bend and become relatively weak. Sorry fi that sounded unprofessional but it makes sense.

I remember when i was growing up in the midwest of the United States, where tornados are very previlent, that after a storm had blown through the town I lived in, someone came across a straw stuck about an inch into the side of a tree. I found it unbelievable, but you can imagine with such strong force and the correct angle it was easy for the straw to penetrate the tree.

The picture isn't very clear, but it proves my point

lightarrow · « **Reply #16 on:** 13/09/2007 20:07:51 »

Quote from: Cujef on 13/09/2007 19:27:28

If you take a straw and hit most any object that is somewhat soft, or not completely solid, you can the straw to go into it. The idea is that you will be hitting the object at the correct angle that the straw itself will be perfectly aligned to be incredibly strong. If you hit it at an angle other than exactly straight the straw will bend and become relatively weak. Sorry fi that sounded unprofessional but it makes sense.

I remember when i was growing up in the midwest of the United States, where tornados are very previlent, that after a storm had blown through the town I lived in, someone came across a straw stuck about an inch into the side of a tree. I found it unbelievable, but you can imagine with such strong force and the correct angle it was easy for the straw to penetrate the tree.

The picture isn't very clear, but it proves my point

I understand. However, in the experiment I performed, I don't simply push the straw against the potato, but I give it a sudden hit (according to what I saw in a program on TV).

Karen W. · « **Reply #17 on:** 13/09/2007 21:22:27 »

yes and it peirces all the way through not just partialy!

paul.fr · « **Reply #18 on:** 14/09/2007 12:07:25 »

How do you not squeeze the straw? If you make a fist, and slowly open it up, until the is the tiniest of gaps to let light through, then this is enough to have a good grip on the straw.
The "stickyness" of the straw in your hand is enough for a good grip.

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A straw through a potatoe, how does it work?

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