NOTHING TO GET TORN
UP ABOUT
BET YOU CAN'T MAKE TWO STRAIGHT TEARS IN
A PAPER TOWEL!
THE SETUP: The tears in this trick must be made at
right angles to each other. Take a single sheet of paper
toweling. Try to rip it in a straight line from one side to
the other. If you succeed, then make the second tear
from top to bottom.
THE FIX: You can't make perpendicular straight-line
tears because paper toweling is formed on a wire
screen, which creates straight lines in one direction.
This is called the grain. The other direction does not
have these unbroken parallel lines.
A force always attacks the weakest point. The parallel
lines of the grain are thinner than the rest of the paper.
So when you tear with the grain, the rip runs down one
of the lines made by the wire and you get a straight
edge. When you try to tear across the grain, the force
attacks whatever point is weakest and a jagged,
irregular line is produced.
Taken from:
Bet You Can’t
Vicki Cobb/
Kathy Darling
Avon Books, 1983