Static Friction: Phone Books & Wood Blocks

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Discussion Overview

The discussion revolves around the mechanics of static friction as it pertains to the interleaving of phone book pages and the analogy to sliding blocks of wood. Participants explore the implications of increased surface contact and the resulting frictional forces involved in this scenario.

Discussion Character

  • Exploratory, Technical explanation, Conceptual clarification

Main Points Raised

  • One participant suggests that interleaving the pages of phone books creates many surfaces that slide against each other, similar to sliding a block of wood on a table.
  • Another participant agrees with this analogy, reinforcing the idea that the increased number of surfaces contributes to the difficulty in pulling the books apart.
  • A hypothesis is presented that interleaving the pages increases the distance between the covers and the middle pages, which may lead to a greater normal force on the pages being pulled apart, thus increasing static friction.
  • One participant emphasizes that all surfaces experience the same compressive force per unit area, contributing to a significant total friction force.

Areas of Agreement / Disagreement

Participants generally agree on the mechanics of static friction in this context, particularly regarding the role of increased surface area and compressive forces. However, the discussion includes varying hypotheses about the specific effects of interleaving on normal force and friction.

Contextual Notes

The discussion does not resolve the exact relationship between the interleaving of pages and the resulting static friction, leaving some assumptions and conditions unexamined.

cragar
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when you take 2 phone books , and inter-lay them page by page , so it makes them hard to pull apart . is this because it is like sliding a block of wood on a table just now you have like 1000 surfaces sliding on each other , is that what is going on .
 
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cragar said:
is this because it is like sliding a block of wood on a table just now you have like 1000 surfaces sliding on each other , is that what is going on .
Exactly right.
 
I would also hypothesize that since interleaving the pages spreads the pages out (i.e., the front and back covers are further away from the middle pages than they would be if not interleaved), that attempting to pull the books apart tends to compress the pages in the middle, increasing the normal force (and thus the static friction). Thus, the harder you pull, the stronger the maximum force of static friction on each page->page contact, especially at the middle pages.
 
The OP had it right, all 1000 surfaces experience the same compressive force (per unit area), so the total friction is large.
 
thanks for your responses , just wanted to make sure what was going on .
 

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