# Mythbusters how to tear a phone book

Knowing the coefficient of friction, which can often be found in engineering handbooks, the maximum friction force can be calculated as:. For most paper, the coefficient of friction is in the range of 0. Phone book paper is on the rougher side, probably 0. Table 1 shows the static friction coefficients for some common materials.

When sitting on the table, the average force on a page is about half the combined weight of the phone books, or 10 Newtons 2. The pressure on each page is then:. Of course this value can change, depending on how the books are supported. When hanging vertically, the applied pressure is considerably weaker but friction is still big enough to support a person's weight. If you really want to make an effort to get the phone books apart, you'll have to attach something to the bindings to get a good grip. Friction over a massive surface.

Usually, when you're dealing with friction over a large surface, the normal force is distributed over that surface. Here, the normal forces are only distributed over the surface of a single page, but you have hundreds of pages in parallel each subject to the same normal force. Thank you for your interest in this question.

Because it has attracted low-quality or spam answers that had to be removed, posting an answer now requires 10 reputation on this site the association bonus does not count. Would you like to answer one of these unanswered questions instead? Home Questions Tags Users Unanswered. Pulling apart two interleaved phone books Ask Question.

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Asked 5 years, 1 month ago. Active 2 years, 10 months ago. Viewed 10k times. Can anyone give a good analysis? Ben Crowell Ben Crowell I would guess it's partly because the paper is bound normal to the spine so there is a bending force created when you interleave the pages.

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Also because the pages are at an angle, when you pull on the spines there is a component of the force you apply normal to the page surfaces. Perhaps the large normal force results from a vacuum being created between the pages? This is too large by 2 orders of magnitude, but that's for a perfect vacuum. Even if the actual vacuum between the pages is a small fraction of this, the result wouldn't be surprising?

Where for a block of stacked papers, individually they can be easily torn apart, but here we don't have any special shape that gives us an advantage in distributing the pressure, but maybe instead here a strong cohesion lies between the surfaces of each pair of paper. But I think John's approach is more sound here. Perhaps it's related to the kind of paper phonebooks are made of?

Perhaps it's related to how thin phonebook pages are?

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## CM: Phone Book Friction

Perhaps the bending force John refers to is sufficient to explain the effect, but I am skeptical of that as well. I'm considering doing some makeshift experiments to test some of these ideas if I have some spare time. Johannes Johannes It should slide at the break and reveal your card. This is also how you can find your page if you accident my close a book. It works quite often.

## CM: Phone Book Friction Under the Maroon Hutch

I believe this is part of the force holding the phone books together Philip Moseman Philip Moseman 1 1 1 bronze badge. Aside 1: I doubt this neat trick would work as well with phone books made of rubber or steel. Aside 2: When shopping for fine wood furniture, you should remove a drawer and examine it.

If the front of the drawer uses dovetail joints you are potentially looking at a good piece of furniture. If the rear of the drawer also uses dovetail joints you most likely are looking at a fine piece of furniture. Most people don't bother to look at all, so most manufacturers just use butt joints the cheapest but weakest of joints. Dovetail joints are immensely stronger but require time and craftsmanship. David Hammen David Hammen 35k 7 7 gold badges 60 60 silver badges bronze badges.

## Researchers explain why it's nearly impossible to separate two interleaved phonebooks

It's not really that much of a surprise when you think about it. MSalters MSalters 4, 12 12 silver badges 24 24 bronze badges. Featured on Meta. Feedback post: Moderator review and reinstatement processes. Rotate your hands to tear the book. Twist the right side of the book up with your right hand while twisting the left side down with your left hand this can be reversed depending on what's comfortable for you.

Maintain a firm grip on the book at all times, and use your pectoral muscles to keep firm inward pressure on the book. The book should begin to tear.

How to Rip a Phonebook in Half!

Rearrange your hands if necessary. Tear through the book. If you're strong enough and maintain a good grip on the book, you may be able to rip the book all the way down the center of its length in one shot. Otherwise you may need to reposition your hands and continue ripping less gracefully. Either way, it will be impressive.