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# Interlacing pages of books - Need help with understanding watch

1. Hello all,

I am working on a science project based upon paper, and I have chosen the affect of friction between two interlaced books. The attachment below is something I have found on the internet, as part of my research..

I don't understand why the Rav = 0.5 * (mass1 + mass2) *9.81. Why is the total mass of the books halved? Could you please explain this?

A.T.
Attached Images
2. Inseparable phone books, science fact or science friction.pdf (66.7 KB, 128 views)
3. (Original post by Atham)
Hello all,

I am working on a science project based upon paper, and I have chosen the affect of friction between two interlaced books. The attachment below is something I have found on the internet, as part of my research..

I don't understand why the Rav = 0.5 * (mass1 + mass2) *9.81. Why is the total mass of the books halved? Could you please explain this?

A.T.
It is considering the average page in the book. So on average there will be a force on the page of half the total weight of the book. This is because only the last page will have the whole weight and the first page will have zero the weight on it. Average is

make sense?

Edit: consider the first page: weight on the first page is so the weight on the second page is and so on untill you reach the last page
The average page is the sum of these weights, devided by the number of pages
4. Right, I see. Thanks for the explanation

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