Brief Description: Students learn about buoyancy by building boats out of various materials.

Grades: K-5

Time: 1 hour

Keywords: surface area, buoyancy, boats, aluminum foil boats, air resistance, density

Lesson Objectives

  • Students will be introduced to the concept of buoyancy
  • Students will use the Engineering Design Process to design, test, and redesign their boats


  • Aluminum foil
  • Clay (NOT play-doh)
  • Saran wrap
  • Duct tape
  • Cardboard
  • Legos
  • Popsicle sticks
  • Coffee filters
  • Pennies (or other objects that can be used as weights)
  • Plastic bin to fill with water


  1. One would expect that an incredibly heavy object (weighing a few tons) would sink in water. A heavy rock will sink to the bottom, so why is a boat any different? How do boats float?
    1. An object will float if the downward gravitational force is less than the upward buoyancy force. An object will float if it weighs less than the amount of water it displaces.
    2. Buoyancy: the ability or tendency to float in water or air or some other fluid.
    3. Displacement: the moving of something from its place or position. If you fill your bathtub with water, what happens when you get in? The water rises! That is because you “displaced” some of the water with your body and it had to go somewhere.
  2. Students are then tasked with building a boat out of the material provided. The boat must be able to float in water. We will also test to see how much weight the boat can carry using pennies.
  3. Allow students to build, test, and redesign for the remainder of the class.
  4. What materials worked the best for boats? What shapes worked the best? Why? What challenges did you face in this activity?

Extensions and Modifications:

  • Challenge the students to build a sail for their boat. Sails use of air resistance to “catch” the air and use it to move. Bring a fan to serve as wind for the sailboats.
  • Classic Intro to STOMP activity: Have students build boats using only aluminum foil.



  • Be aware that the bottleneck in this activity is the testing: students finish their designs around the same time, and therefore all want to test at the same time.  Make sure you have enough testing stations so that their design process is not impeded.

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