Re: when we crush a paper why it opens itself slowly?

This happens for the same reason that you should see similar behavior in
most materials when you try to crush, bend, or stretch them.  What you are
seeing is a combination of “plastic” and “elastic” deformation.  Plastic
deformation is permanent, while elastic is not.  Elastic deformation
usually occurs before plastic deformation, and is responsible for making
materials “springy”.  The good example would be to bend a paper clip.  If
you bend it a little bit, it springs right back to where it was.  This is
elastic deformation.  If you bend it farther, it won’t spring back to its
original position.  This is plastic deformation.  However, when you bend it
really far, you will notice that when you let go, it does spring back a
little bit.  It won’t completely spring back to where it started (since you
caused some plastic deformation), but it does spring back a bit.  The same
thing happens when you crush paper.  You have caused some plastic and some
elastic deformation.  For the most part, it stays crumpled because of the
plastic deformation.  But when you let go, it slowly springs because there
was also some elastic deformation.  Hope that answers your question.

Your Mad Scientist,
Mike Scannell