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Necessarily make a profitand recorded how the tip of the@DOWNTOWN4 - 27 TICKETS THAT GUARANTEE LOTTERY WINand recorded how the tip of the
crack propagated. Across many
recordings, these cracks moved
unexpectedly quickly. The fastest
were about 30 per cent faster than
the speed of sound. Even when the
researchers skipped the notch-
making step, some still travelled
15 per cent faster than the speed
of sound (
Science
, doi.org/kmcv).
Fineberg says theoretical and
experimental studies of materials
that crack have so far shown that
cracks can’t propagate faster than
sound. This is because the speed
of sound reflects how quickly
mechanical energy can move from
one part of the material to another,
which must happen for it to crack.
For common stretchy objects like
springs, the relationship between
the force that stretches them and
how much they elongate is simple
and direct, but that is not the case
for every part of these gels, says
Alain Karma at Northeastern
University in Massachusetts,
who wasn’t involved in the work.
“There is no theory that really
describes how a crack propagates
at a very high speed in this kind
of elastic medium. And it’s really
puzzling how you could bring
energy to the crack fast enough
for this behaviour,” he says.
Resolving this puzzle could
help us understand dangerous
events that involve fractures like
earthquakes, where some cracks
propagate very quickly.
❚
Supersonic cracks
seem to be breaking
the laws of physics
“It’s really puzzling how
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