Page 168 - Engineering in Nature

Engineering in Nature

From a stationary position, some
small fish can reach their maxi-
mum speeds in as little as
1/20th of a second. In that

time, they can produce a
propulsive force up to four
times their own weight.
To fully understand the
significance of these figures,
consider that sports cars can
accelerate from 0 to 100 kilome-
ters per hour in between four and
six seconds, and need a great deal longer
to reach their maximum speeds.
Another point is that. Fish exhibit these superior performances un-
derwater and in some species, even against the current. Since the re-
sistance of water is greater than that of air, clearly that the fishes'
performance is a most superior one.
The salmon is no doubt the best example in this regard.
As we've seen, salmon can lay their eggs only if they can return
from the sea and reach the rivers where they were born. In order for
salmon reach their birthplaces, they must constantly swim against the

current of the river. They may have to overcome water-
falls in front of them, leaping four meters forward
and two meters above the level of the water. To
do so, salmon need to leave the water at a
speed of 24 kilometers per hour (15
miles/hour). Falling after such a leap
Air sac
could be lethal for many creatures. Yet the

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