Christian Homeschool Resources & Homeschooling Advice

Salt, Boats, and Submarines

  • Melissa Pinkley Home School Enrichment
  • Updated Aug 06, 2009
Salt, Boats, and Submarines

My family lives near a lake, so whenever the temperatures begin to rise, my children can’t wait to play in the water. They like getting wet! How about you? Do you enjoy boating and playing in the water? Have you ever been on a submarine? I have always thought it would be fun to see below the water while riding in a submarine! The experiments below will help us learn about water, boats, and submarines, and they might even get us a little wet.

Experiment #1: What’s the Difference Between Salt Water and Fresh Water?

Okay, you may be chuckling at me and thinking, “One has salt and one doesn’t.” You are very funny! This is true; however, this causes some differences that you may not be aware of. Have you ever heard of the Dead Sea? It’s a salt lake located near Israel. It is actually one of the world’s saltiest bodies of water. What do you think happens when people try to swim in the Dead Sea? See if you can figure the answer out by doing this experiment.

Items Needed:

  • 1 jar
  • Modeling clay
  • Table salt
  • Measuring tablespoon
  • 1 marker lid
  • Tape, small stickers (optional)

First, fill the jar ¾ full of water. Next, place enough clay inside the marker lid so that it will sink when placed in the jar of water. You might want to mark the level of the lid somehow on the outside of your jar with the tape or small stickers. After that, add 1 tablespoon of the salt into the jar. Observe if there is any change. Then continue to add 1 tablespoon of salt at a time until 5 tablespoons have been added. Make sure you observe the level of the marker lid after each tablespoon is added. What happened? Based on this experiment, what do you think would happen to people who went swimming in the Dead Sea?

Why do you think this happens? Well, fresh water is less dense than salty water. As the amount of salt increases, the water gets even denser. Because the water is basically thicker when it has lots of salt in it, it is easier for an item to float rather than sink. 

Experiment #2:  Build a Boat that Floats!

Have you seen the many different varieties of boats? Some different types are pontoon boats, motor boats, barges, cruise ships, and rowboats. What shape of boat floats best? In this experiment, you will try your hand at making a few boats and testing which one stays afloat the best.

Items Needed:

  • 3x5 cards (enough for each person to make at least 2-3 boats)
  • Aluminum foil
  • Duct tape
  • Straws (optional for support)
  • Pennies (at least 50)
  • Bathtub, sink, or large container

Take the items gathered, except the pennies and bathtub, and make two or three boats. Remember, you are trying to make a boat that will float the best. Once you have created your boats, take them to the bathtub with at least 4 inches of water in it. Set the boats on the water. Do all of them float?

Add pennies one at a time to each floating creation. Continue adding pennies until your boat sinks or you run out of pennies. Which boat stayed afloat the longest? Why do you think this boat won the floating contest?

Experiment #3: Make Your Own Submarine!

My son did this experiment several years ago, and it was so much fun. I loved watching his homemade submarine rise and sink in our bathtub. I hope you have as much fun as we did learning how a submarine works.

Items Needed:

  • A plastic drinking bottle (1-2 liter)
  • Plastic or rubber tubing
  • Modeling clay or sealant
  • A container to house your submarine
  • Bathtub, sink, or large container

First, puncture or drill a hole through the bottle’s cap with adult supervision. Then run the plastic tubing through the hole into the bottle. Make sure you leave enough tubing on the outside of the bottle so that when the bottle is submerged, there is enough tubing to reach out of the water. Use your modeling clay or sealant to seal off the gap around the tubing at the cap.

Next, make a small hole in the bottom of the plastic bottle. Make the hole small enough that you can cover it with an object such as your finger. Cover the hole and then fill the plastic bottle all the way up with water. Put one side of the tubing into the bottle, and screw on the cap, making sure you keep the hole in the bottom of the bottle covered.

Place the bottle in a sink, bathtub, or large container that has enough water in it to cover the bottle by at least 2 inches. Now uncover the hole in the bottom of the bottle. The bottle should sit on the bottom of the tub. Next, take the part of the tubing that is out of the water and blow into it as hard as you can. Your submarine should rise to the surface.

If your bottle does rise, then you have successfully created your own submarine. The most advanced submarines in the world operate the same way—by alternately filling chambers with air or water in order to rise or sink. Of course, they have sealed areas that allow passengers and items to be safely transported below the depths of the water.

You can learn more about submarines by visiting these sites:

  • This is a site about one of the Civil War submarines. It includes a simulator that allows you to try and get the sub to complete its mission:
  • To learn even more how a submarine is able to work, visit 

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Melissa Pinkley enjoys life with her husband, Wes. They learn a lot from their four children: Ben, Micah, Levi and Abigail. Homeschooling goes on 24/7 for the whole Pinkley family. They have been homeschooling for 6 years.  The Lord is gracious and continues to help them follow Him.

Originally published in the May/Jun ’09 issue of Home School Enrichment Magazine.