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 of fins.

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 to survive.