July 11

Welcome to the Dive Deeper Weeklong Challenge


Dive Deeper Weeklong Challenge #6

In contrast to other fish, who have bladders filled with gas, sharks have a liver filled with low-density oil that is similar to vegetable oil.  In this experiment vegetable oil is used to explore the subject of buoyancy and make your "sharks" float.

Supplies Needed:

Here's what to do:

Step 1:  Attach the pennies to the toilet paper roll (as shown)

Step 2:  Use the tape to attach your shark to the other side of the toilet paper roll. (as shown)

Step 3:  Now it's time to place the shark in the water. What do you think is going to happen?  Is the shark going to sink or float?

Step 4:  BALLOON TIME!  Slowly fill the balloon with 1/3 cup of vegetable oil and tie it up.  (warning: if you spill the oil, the balloon will get very slippery, which makes it hard to tie it)

Step 5:  Insert the balloon inside the toilet paper roll.  It might take some good squeezing action to sneak it in.  Try to center it inside the roll.

Step 6:  Place your noticeably heavier shark in the water a second time. 

Is it going to sink or float?

The Science Behind the Experiment

If you hold a toy shark in the air and let it go, would it float in the air or drop to the ground? Of course, it drops because of the pull of gravity.  Do you know that the same pull of gravity affects fish in the water?

But do fish drop to the bottom of the ocean because of the pull of gravity? No!  They float!

Fish developed a great adaptation to balance the pull of gravity with the upward push of buoyancy.  Buoyancy is the upward force from the water to stay afloat.

Most fish have a bladder filled with gas (http://www.sharksinfo.com/buoyancy.html).  This is what keeps them balanced in the water.  Sharks do not have such a bladder but they have developed different adaptations that help them achieve the same result. These adaptations are no bones, larger liver, and steering fins.  

Sharks' Adaptations

Sharks do not have bones, but cartilage, which is about half the density of bones. However, the shark’s body is still heavier and denser than water, so they use their fins to keep moving and propelling them forward at all times. Lastly, sharks liver is 25-30% of their body mass (only 5% for mammals). This liver is filled with low-density oil (similar to vegetable oil we used in the experiment) and it acts like a swim bladder of other fish by giving them neutral buoyancy.  

Neutral buoyancy meals that an object within a liquid is neither rising nor sinking, but maintaining the same depth. Unfortunately for sharks, their wonderful liver is used in a number of cosmetic products from lip balms to suntan lotions. Never buy these! Sharks are nice!