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  • Gloria Hoffner

Shark Week - How do sharks float?

There are more than 350 types of sharks in the world. They range from a whale shark, up to 46 feet long, to a spinn

ed pygmy shark between seven to eight inches long.

Based on the fossil record, scientists believe sharks have lived on the Earth for more than 420 million years.

Megalodon was the largest shark that ever lived and the largest predatory creature on the planet. Based on fossilized teeth, which were 7 inches long and serrated, researchers believe this shark grew to be at least 60 feet and weighed 100 tons or more. Its jaw closed on a victim with a force of between 10.8 and 18.2 tons. In comparison, today’s great white shark has a jaw crushing strength of 1.8 tons and a lion produces about 600 pounds of jaw closing pressure. Some scientists estimate that Megalodon consumed about 2,500 pounds of food a day.

Megalodon became extinct over 2 million years ago. There are several theories on extinction including, change in ocean temperatures, land mass and among the creatures in megalodon’s food supply.

What megalodon and today’s sharks have in common: all sharks are fish, all sharks’ teeth are replaced throughout its lifetime and shark skeletons are made of cartilage, not bone like most fish. Sharks breathe under water through gills, like fish and unlike whales which as mammals must surface to breath air.

A shark can grow more than 30,000 teeth in a lifetime with the most powerful bite of any creature in the world. This does not mean they kill the most people in the world. Unlike in the movies, sharks are not a huge threat to human life. There are less than 10 reported human deaths by sharks annually worldwide.

Sharks can live in both fresh and salt water and reproduce in three different ways depending on the species. Some sharks are born alive from the mother, some develop from an egg inside the mother and then are born and some hatch from an egg laid outside by the mother. A liter of shark ‘pups’ as they are called can range from one to 100 depending on the species.

A baby shark is on its own from the moment of birth. Most sharks live about 20 years, but a Spiny Dogfish Shark can live to be 100 years old. A shark can smell one drop of blood in three miles of water. Shark skin has the texture of sandpaper.

Experiment: How Do Sharks Stay Afloat?

Materials: Empty toilet paper tube, three pennies, packing tape, 12 inch balloon, ¾ cup of cooking oil and punch bowl filled with water.

Process: Tape three pennies to one side of the toilet paper roll, spaced evenly apart, and wrap the roll in the tape leaving the sides open. Fill the balloon with ¾ cup of cooking oil and tie off the end of the balloon. Place the toilet paper roll in the water and observe. Removed the toilet paper roll, insert the balloon and observe.

Result: The toilet roll with the pennies represents the density of the shark. The cooking oil in the balloon represents the oil in a shark’s liver. The shark floats because the liver oil is less dense than the water.

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