Investigate How Objects Sink or Float in Different Types of Water

By Priyanka Lamichhane

Jul 2, 2021

15 min activity

The Kratt Brothers love exploring all corners of our planet, including the oceans! And it’s a good thing they do because Earth’s oceans make up about 70% of the surface of our planet. That’s a lot to explore! Ocean water is very salty. All that salt comes mainly from salt in rocks. The salt makes its way into the ocean through rivers and streams. The oceans take in salt from most of the rivers and streams around the world.

Together with your child, explore the differences between saltwater, freshwater, and water with baking soda added. Then, observe what happens when an object is added to each glass. Ask your child to make observations throughout the experiment, focusing on what each glass of water looks like and the similarities and differences they notice.

Materials

Directions

Line up three glasses. Add two tablespoons of salt to the first glass, add two tablespoons of baking soda to the second glass, and leave the third glass alone. Using your sticky notes or paper, label each glass: saltwater, baking soda water, freshwater.

Add enough warm water to fill each one of the glasses more than halfway and stir the saltwater and baking soda water until the substances are dissolved. Observe each glass together. Ask your child questions such as, “How has the water in the first two glasses changed? What do you notice about them that’s different than the glass with only water?”

Next, tell your child that you’re going to add your plastic blocks to each glass. Help your child predict what will happen to the blocks. Ask your child, “Will they all sink? Will they all float?” Once the salt and baking soda are dissolved, place one block into each of the glasses. Watch what happens to each block as they enter the water. Ask your child if their predictions were correct.

Explore Further

We know that the oceans are salty, and so are seas and some lakes around the world. We also know that streams, rivers, and many other lakes are full of freshwater, as are glaciers and icebergs. But a few bodies of water are in between — a mix of saltwater and freshwater. They are known as brackish. Brackish water happens in places where saltwater and freshwater meet, such as the entrance to a bay or where a river empties into an ocean.

Invite your child to explore brackish bodies of water and the types of animals that live in them. Are there some animals that can survive more than one type of water? Exploring the Chesapeake Bay, located on the east coast of the United States, is a good starting point. This bay gets half of its water from the Atlantic Ocean and half from the many rivers and streams that flow into it. As you explore with your child, ask them to think about the similarities and differences between freshwater, saltwater, and brackish water.

Want more “Wild Kratts” activities? Check out the Creature Power Generator Game and the Test the Strength of Spider Webs activity to continue the fun!