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Jet Propulsion in the Ocean: Make a Speedy Octopus

This article appeared in the August 8, 2014 edition of the Davis Enterprise.

By Lisa Justice

Special to the Enterprise

 

With eight legs to choose from, it’s no surprise that an octopus has lots of different ways to get around.  They can crawl across the ocean floor or underwater rocks with their legs.  Some have fins to help direct swimming.

 

But by far the fastest method is jet propulsion.  The octopus can shoot itself through the water like a rocket! 

 

Later this month, some of Explorit’s summer science campers will experiment with demonstrating this phenomenon.  You can join them at home with a few simple supplies.

 

You will need: a balloon, some food coloring, a binder clip or snack clip and a tub of water.  If you have a small pool, that works well also.  The more room you can give the balloon to move around, the better.

 

Fill the balloon most but not all of the way with water.  Add a drop or two of food coloring to help you see tell the difference between the water in the “octopus” and the water in the pool.

 

Instead of tying off the end, clip it closed with the binder clip.  That way you can easily release the balloon when you want to.

 

Gently place the balloon into one end of the tub of water.  Make sure the body of the balloon is pointing toward the middle of the tub and the end of the balloon is pointed toward the side.  Be careful; you don’t want it to pop! 

 

When you’re ready for a show, unclip the end of the balloon and watch what happens.  You should see the water inside the balloon rushing out and the balloon zipping around the tub as it deflates.

 

What’s going on here?  It has to do with potential energy.  When the balloon fills with water, it gets stretched out.  Just like a rubber band, it will want to snap back as soon as it can.

 

When the balloon is unclipped and the water can start moving out, the sides of the balloon will start to snap back, squeezing the water out even faster.  An octopus uses the same technique if it needs to make a speedy get-away.

 

An octopus can use its mantle (the round part of its body that houses its internal organs) like a balloon.  It fills the mantle with water, and when it’s ready to take off the octopus squeezes the water out of a small hole called the siphon. 

 

The effect is just like unclipping the balloon except the octopus uses its muscles to squeeze out the water.  As the water is ejected in one direction, it pushes the octopus in the opposite direction and changing the position and angle of the “jet” siphon, it can steer where it wants! The octopus gets propelled quickly through the water allowing it to pounce on prey or evade a predator.

 

Fill your balloon up again and repeat the experiment as frequently as you like.  Try adding different amounts of water to see if you can change the speed or distance your balloon octopus travels.

 

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Explorit’s coming events:

 

  • Explorit’s Beautiful World: Science and Art exhibition is open to the public every Wednesday, Saturday and Sunday, 1:00-5:00 p.m. and every Friday, 3:00-6:00 p.m.  Admission is $5.00 per person; Explorit members, teachers and children 2 and under are free.
  • Interested in membership?  Think your Explorit membership may have lapsed?  Call Explorit at 530-756-0191 to check or sign up!
  • Birthdays are back at Explorit!  Call Explorit at 530-756-0191 for more information or to book your party.
  • Save the date:  Sunday September 7th!!  Our exciting “Final Blast Festival and Chemistry Show” will once again wow you and your kids!  This event celebrates the end of our Summer Science Camp season and fun way to start the new school year!

 

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Explorit Science Center is located at 3141 5th St. For more information call (530) 756-0191 or visit http://www.explorit.org, or “like” us on Facebook at www.facebook.com/explorit.fb.

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