If a tree falls in the woods...

When we fold a paper and then tear it, why does the tear-path follow the fold?

Paper is an aggregated web of vegetable cellulose fibres usually prepared from wood pulp. The fibres in this planar web are bound to each other by a kind of bonding known as hydrogen bonding.

The internal structure of paper can be described as follows. There is a distribution of the fibre sizes; the finer ones interpenetrate into the web of larger ones and small clusters of these hold together the larger ones and so on.

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