These are great questions. You may have
noticed that things travelling fast through the
air or water usually have fins. Boats, planes,
torpedoes, and fish all have tails, fins, or
keels. Without these, they will start to tumble,
which wastes energy and makes it difficult to move
in a straight line.
Sharks “wag” their tails back and forth to move
forward. Without a dorsal fin, their whole bodies
would flop from side to side a lot. The dorsal
fin keeps them moving in a much straighter line.
You can experiment with this yourself with the
help of an adult. Get a jar or fish tank full of
water, some clay, and some sort of stiff plastic
that you can cut into fins. The recycle bin is a
good place to look. Try dropping clay of
different shapes into the water. Start at the
surface of the water to avoid extra splashing.
Then see what happens when you add different types
Unfortunately, without a dorsal fin a shark
will not be able to survive. Sometimes if there's
damage in nature, the shark might be ok, but
without a complete dorsal fin, it is hard for them
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