How to rip a phone book apart

Actually it seems right. Why does this work? I found the following online discussion from , the same year in which the episode aired:. Posts 8, 27, and 36 seem the most relevant. A year has passed since this question was posed, and as luck would have it, this week a paper appeared on the science preprint repository ArXiv discussing exactly this phenomena. The preprint PDF is available here. Key to the phenomenon of spectacular friction forces between two interleaved phone books is a simple geometrical conversion of the traction force to an orthogonal component which enhances the load and thus the friction.

This geometrical conversion i. Due to the stacking of the sheets in the contact region, the normal forces due to the geometric conversion cumulate towards the inner sheets, which results in the friction force between the interleaved books to depend exponentially on the number of sheets involved. The fact that the anomalous geometrical amplification of friction results solely from the slopes that the sheets make as they approach the contact area, can easily be verified.

As the authors state: one can realize an interleaved-book system with non-sloping sheets by removing alternating sheets in two notepads. In such a case, the books can be easily pulled apart. Figure with caption from paper "The enigma of the two interleaved phonebooks". Each page between pages has some static friction force threshold based on the effective coefficient of friction and the normal force compressing them even if it's just gravity.

Like MSalters said, the fact that there are hundred of pages doing this means you have a very large area over which it's applied, but that's not what makes the difference.

Solved: the mystery of why it's impossible to pull apart interleaved phone books

That normal force applied over a massive area would mean nothing, but the fact that the pages are stacked means that the normal force is multiplied by the number of touching surfaces! To think of it another way, each page between pages has a full normal force-worth of friction, while the tangential pulling forces are distributed between all of the pages. Thus, the friction each page has to hold is relatively small. Still, they measured 8, lbs of force to pull those books apart. If you guess that each has about pages total , that's around 10 lbs per page, which would be stretching it even if the pages were taped or glued together!

MythBusters - Phone Book Friction

So there's clearly something else at work here besides normal friction. I think one important effect is that the interleaved pages are thicker together than each of the books' spines, so when pulling the books apart, it compresses the pages together, resulting in a much bigger normal force. If you just hold a ream of paper in your hands, it has no trouble falling apart.

Mission Cliffs

I also want to say that there must be some electrostatic phenomenon going on. Phone books and magazines have thin pages.

Step 2: Cut It

Sliding things across each other is a great way to generate static electricity. Normally it's done with different materials, and I'm not being particularly scientific here—this is a hunch, but I feel like phone books and magazines do tend to have staticky pages it's been a while since I've touched either, but hey. Sliding that many static-inducing surfaces across each other could generate a lot of charge separation, which would take a lot of energy to do.

Again—I don't have much evidence to back that up, it's just my intuition trying to rationalize the fact that it took two tanks to separate a pair of interleaved phone books! Take a deck of cards. Squeeze them down on a flat surface. Break it in half. Leave the bottom half on the table. Now look at the card and set the deck back together. For the trick, push the side of the top half of the deck. I set up a simple experiment to test the question if there are more forces at work than static friction. The experiment was one notebook, the clamping notebook, sat along the edge of a table and another notebook, hanging notebook, hung from it by a sheet sandwiched near the bottom of the clamp.

The clamp was secured by its spiral using some pens and tape. I can go over the physics, if you like, but I had calculated it would take the whole weight of the clamping notebook to hold the hanging notebook in place. There appeared to be a force equal to that of static friction assuming a standard coefficient of static friction for paper that was unaccounted for. I think what best explains this is whatever explains the anecdote of the card trick. There must be some kind of air pressure missing from the air being squeezed out between the pages.


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I noticed it a great deal in the experiment, the first time the hanging notebook slipped out there was 16 pages pressing down on it. It stood stationary a few seconds before falling. Lower amounts of pages also held but only for a few seconds. It had a consistent delay, even when only one sheet and the cover clamped on it, very little weight, after pressing down there was a several second delay while air was drawn in before the notebook slipped outright. EDIT: There seems to be some claim that 1. By looking at several sources online I found the coefficient of friction seemed to be close to 0.

This is important because I calculated a coefficient of friction from my tests of 0. This seemed to agree with a search, for example Fuji printers says it is between 0.


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An average of 0. Again, in my experiment there is no "binding", both literally and figuratively, so there is an additional force, other than static friction, that nearly doubles the holding power. Static friction and the normal force most certainly do play key roles here.

The thickness of the doubled-up phone books where the pages interleave is twice as thick as the individual phone books at the binding. Tension results in a compression at the middle that results in a good-sized normal force, and hence a good-sized static friction force. Another and perhaps more important factor that comes into play is that paper is a somewhat unique substance.

Tips for tearing a telephone book apart?

Apply tension to a rubber band or steel rod and they stretch and get thinner. Most substances work this way; they have a positive Poisson's ratio. Paper doesn't act like this. Apply tension to paper and it gets shorter and fatter. Paper is one of those rare auxetic materials with a negative Poisson's ratio. Place your thumbs on top and your fingers underneath one of the edges of the phone book excluding the edge that is the binding.

You can either tear the phone book by its length or its width — either way it will be impressive. Brace the phone book on your hip or thigh and hold it tightly in both hands.

Keeping your thumbs on top of the V, begin bending the sides of the phone book down. The cover and the top few pages should begin to split apart. Keep bending until you tear all the way through to the other side. Letting out a manly yell at this point can help.

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Can You Compost Phone Books?

The thicker the phone book you use, the harder this part is. I was able to tear through a two-inch phone book easily; a four-inch phone book was a beast, but still doable. Just finish tearing through the book by pulling the two sides apart. You may need to readjust your hands on the book to get a better grip. You just tore a phone book in half with your damn, bare manly hands.


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Time to impress your friends and make the ladies swoon with this virile feat of strength. Illustrations by Ted Slampyak.