Sink or Float: Explore a Boat

Children will make rafts out of craft sticks and test their ability to float.

Birds Nest

Lesson Objective

Children will understand that boats are a form of transportation and will experiment with the concepts of “sink” and “float.”


What You'll Need

  • A large clear plastic tub
  • A selection of objects that sink and float; include heavy objects, light objects, and objects that are made of different materials (such as plastic, wood, paper, Styrofoam, metal) – 1 per child, plus a few extra
  • Craft sticks – about 15 per child
  • Glue
  • Large piece of chart paper and markers 
  • Water

What To Do

Note: This activity requires time for the project to dry before completing the lesson.

  1. Prepare a chart with two columns: one side with the word “sink” at the top and the other side with the word “float” at the top.
  2. Add water to the tub, a little more than half full.
  3. Tell the children that they are going to do an experiment. Display the things that you found in the classroom.
  4. Give the children time to talk about the items and to name them; maybe talk about what kind of materials they are made from.
  5. Pick one of the objects. Tell the children you will put it in the water. Ask what they think will happen. Invite everyone to guess what might happen.
  6. Put the item in the water. Listen to what the children say. Are they using the words “sink” or “float”? Ask the children, “What is happening? Is the _____ resting on the top of the water, or did the ____ go down into the water? Did it sink or float?” Record the information in the proper column on the chart. Write the name of the object, and draw a picture of it.
  7.  Let each child take a turn selecting an item and testing it to see if it sinks or floats. Record the results on the chart. Ask children if their predictions were correct. If not, ask, “Why not?”
  8. Tell the children that when people use boats, the boats float on the water.
  9. Tell the children they are going to make a kind of boat called a raft. Distribute a set of craft sticks to each child (10–15 sticks). Show the children how to lay 5 or 6 sticks next to each other on the table. Then, put glue all over one side of another stick. Lay it sideways across the sticks that are on the table. Do this two more times. Let the rafts dry.
  10. After the glue has dried, let the children take turns floating their rafts in the tub of water. Give them the opportunity to experiment with the rafts as transportation. Put coins or small objects on the rafts.

Guiding Student Inquiry

  • Tell me about some of the things that floated. Why did they float?
  • Tell me about some of the things that did not float. Why didn’t they float? 
  • Is there something we can do to any of the items to make them float?
  • How many items can the rafts hold before they tip or sink? 
  • Did all of the rafts hold the same amount of items before they tipped or sank?
  • What would happen if we used more water in the bin? What if we used less water? What if we used a larger bin or a smaller bin?
  • How do boats and ships float when they are so big and weigh so much?
  • How do boats float with people in them?

Explore, Extend & Integrate

  • Put some of the finished rafts with the other toys in the water table if you have one.
  • Encourage children to make rafts and boats in the construction center, and talk about places where boats can travel to that cars may not be able to travel to.
  • Let the children use the discovery or science center to experiment with making boats out of a variety of materials. They could use pieces of foam, plastic containers, tin foil, cardboard, and paper. Let the children make predictions about their boats and test them in the sink or at the water table.

Check for Children’s Understanding

  • Was each child able to experiment with the different objects and compare and contrast the ones that floated with the ones that sank?
  • Did children understand why objects floated?
  • Did children understand why objects sank?


Did You Know?

Some things float because they are lighter than water and are buoyant. Buoyancy is the upward force needed from water for an object to stay afloat. Buoyant forces are why we feel so much lighter when we are in a swimming pool or bathtub. Gravity plays a part in buoyancy because gravity pushes everything down. Fluids have a force that pushes up. When something heavy, like a rock, is dropped in water, the water pushes up on it with a force equal to the weight of water it displaced. The rock weighs more than the amount of water it displaced and will sink. Although bigger than a rock, a beach ball weighs less, displaces very little water, and will float on the water.

In order for a boat to float, it must be designed in a way that it will not easily tip over and must be made of materials that will help it float. Boats have been a form of transportation used by many cultures throughout history. Originally, boats were made from trees and wood. Boats can include rafts, canoes, kayaks, gondolas, sailboats, and motorboats. Larger boats are called ships, and they travel on lakes, seas, and oceans. Today, boats and ships are made from a variety of materials, including plastic, steel, aluminum, fiberglass, and wood. Boats and ships are used for transportation, fishing, entertainment, warfare, and providing safety.  

Vocabulary: Child-Friendly Definitions

  • float – to rest on the surface of a liquid without sinking.
  • sink – to fall slowly to a lower level.
  • boat – an open vehicle, smaller than a ship, that moves on water.
  • ship – a large boat that carries people or things through deep water.
  • transportation – the act of moving things or people from one place to another.
  • raft – a flat platform made of materials that can float, used to carry people or goods.

Lesson Tips

  • This experiment requires the children to play in the water. You may want to put some plastic on the floor under the tub holding the water. If the day is warm enough, you can do the experiment outside.
  • You might want to have the children wear smocks.


  • Boats by Byron Barton
  • Busy Boats by Tony Mitton
  • Boats by Anne Rockwell
  • Who Sank the Boat? by Pamela Allen
  • Early Reader: Sink or Float by Lynn Salem and Josie Stewart

Home School Resources

Home educators: use these printable lesson PDFs to teach this lesson to your home schoolers. They're available in English and Spanish.

Home/School Connections

Las Conexiones a la Casa

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Content Provided By

Common Core State Standards Initiative – These lessons are aligned with the Common Core State Standards ("CCSS"). The CCSS provide a consistent, clear understanding of the concepts and skills children are expected to learn and guide teachers to provide their students with opportunities to gain these important skills and foundational knowledge [1]. Visit the CCSS