Page 167 - Engineering in Nature

Harun Yahya

created in such a way as to eliminate that effect.
At the same time, the water acts on the head with a vertical force
during movement. All this gives rise to the movement of the head
part of the fish being smaller to that of the tail. It is this difference that

allows the fish to move in the water.
How quickly the fish moves depend on how rapidly the axis pass-
ing through its backbone moves to right and left. The speed increases
as the fin nears the axis, and decreases as it moves away.

• An Optimally Efficient System
How efficient is this system? When we compare a waving tail and
a submarine engine, what kind of results emerge?
Professor Richard Bainbridge of Cambridge University and his
team set out to answer these questions with observations from an un-
derwater camera.
Their observations of a fish that was still and calm revealed that
when alarmed, it went into action at an amazing speed.
From a standstill, a small freshwater fish can move forward 10
body lengths in the space of one second. A 20 cm (8 inch) fish can
achieve a speed of 8 kilometers (4 miles) per hour. Speed increases
with the size of the fish. Professor Bainbridge observed that a 32 cm
(one foot) long fish achieved a sustained speed of 13 kilometers (6.5
miles) per hour. That speed is directly related to the frequency at
50
which the fish moves its tail. The more it waves its tail in a short pe-
riod of time, the greater the speed.
In swimming, fish expend large amounts of energy. However, sud-
den acceleration is vitally important to them, since fish need sudden
bursts of speed for hunting and to escape from predators.

Adnan Oktar
165