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Punching
Through
 Did
you expect the strip as a whole to remain in place while the BB
punched through the central portion? If you were surprised, consider
this:
The area of the strip that first made contact
with the BB was accelerated immediately. This area pulled on
surrounding areas, exerting elastic forces to accelerate them. These
areas, in turn, pulled on portions of the strip even further from
the impact site. This chain of events did not travel instantaneously
up and down the strip. The BB was moving quickly enough that it had
time to penetrate the strip before the disturbance could reach the
pushpin and pull the strip free.
Find out
how a speeding BB can be stopped by a flimsy piece of
elastic.
Find out how the
photos were taken.
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Try
this problem:
The BB shows up as a bright,
blurry spot below the 11 cm mark. Assuming that the BB is
traveling at 150 m/s at the instant shown, estimate the
amount of time it took the BB to pass through the strip.
What other assumptions do you have to make?
Measure
the speed of the BB for yourself. |
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