Floating and Sinking

Submitting Organization: Smithsonian Science Education Center 

Grade Level: 4th Grade – 6th Grade

Subject Area:  Engineering 

Standards Alignment: Next Generation Science Standards

3-5-ETS1-1, 3-5-ETS1-2, 3-5-ETS1-3; Science & Engineering Practices

Description of the Activity: In this activity, students will investigate the effect boat size has on the number of marbles it can keep afloat. Students will construct three different sized models of their design. For each design, students should place it in the water and then gently push down on it until it sinks. Students should describe how “pushing down on the boat” feels. Students might say that they could feel the water pushing up. Encourage students to discuss and describe this upward push of the water against the boat.

Ask students to use this experience to predict and then test how many marbles each boat will be able to keep afloat. Encourage students to add marbles one at a time and to observe how the boat moves down in the water as they add each marble. Ask students to record the size of the boat, a sketch of the design, difficulties faced during testing, prediction of the number of marbles each boat will hold, and then the actual number of marbles each boat did hold.

Discussion Questions:

  • What variable did you control for in this investigation?
  • What difficulties or failure points did you identify during testing?
  • How does the size or design of their boat affect the number of marbles it can keep afloat?
  • Why do you think some boats can be so large and heavy and still float?

Resources Needed: 

  • Plastic tub
  • Water
  • Aluminum foil
  • Marbles (or pennies)

Link to further resources: