When
tearing an object, there is a certain amount of
energy required to start the
tear and a certain amount of
energy per unit
length required to continue it. In most cases, the
energy required to start the
tear makes up the greatest part of the total
energy required to
tear something in half. Think about tearing a piece of
paper: the hardest part is right at the beginning; once it starts to
tear, it comes apart easily. This leads to the somewhat
counterintuitive fact that
tearing an object along a perforated line requires more effort, not less. The
perforations actually only assist in keeping the
tear straight.