Whatever Floats Your Boat

4.1 based on 78 ratings

Updated on May 09, 2013

Grade Level: 3rd - 6th; Type: Physical Science


To explore how the shape of a boat affects its density and how much weight it can float.

Research Questions

  • Why do some things float and others sink?
  • How does the shape of something affect its ability to float?

Why does a paperclip sink in a glass or water, yet a huge aircraft carrier float? In this investigation, the concepts of density and water displacement are explored. The denser an object is, the more easily it sinks. In order to make something float, the density must be adjusted to be less than the water. Adjusting the shape of an object is one way to change its density. This is the basic theory behind the Archimedes’ principle.


  • modeling clay, ball about 1” in diameter
  • clear, large bowl, bucket, or tub
  • water
  • marker
  • ruler
  • camera or paper and pencil for sketching
  • 20 pennies
  • small scale

Experimental Procedure

  1. Gather the necessary materials.
  2. Pour water the bowl, bucket, or tub until the water level is about 3” from the bottom.
  3. Mark the water-line on the bowl, bucket, or tub.
  4. Place the ball of clay into the water. Record the results including the amount in inches that the water raised above the water-line.
  5. Mold the clay into a boat. Take a picture of the boat or sketch a picture of it. Place the boat into the water. Record the results again noting the water-line. Continue to model the clay until you get a boat that will float. With each adjustment to the boat, take a picture or sketch.
  6. Weigh a penny and record the weight.
  7. Add one penny at a time to the boat and record the results including the change in the water-line until the boat sinks.
  8. Make adjustments to your boat in order to allow all 10 pennies to float. Take pictures of or sketch any adjustments in the boat.
  9. Analyze the data to conclude how the shape of a boat affects its density and its ability to carry weight.

Terms/Concepts: density: the heaviness of an object for its size displacement: the exchange of space between one substance by another; For an object to float, the upward push of the water must be the same as the weight of the water being displaced by the object. To cause an object to float, the density of the object must be adjusted to equal the density of the water being displaced.


“Why can boats made of steel float on water when a bar of steel sinks?” at http://science.howstuffworks.com/science-vs-myth/everyday-myths/question254.htm “Eureka! The story of the Archimedes Principle” at http://quest.nasa.gov/aero/planetary/archimedes.html “Archimedes’ Principal” at http://physics.weber.edu/carroll/archimedes/principle.htm “Archimedes’ Principal of Buoyancy” at http://www.grandpapencil.net/science/archimed.htm

Nancy Rogers Bosse has been involved in education for over forty years - first as a student, then as a teacher, and currently as a curriculum developer. For the last fifteen years she has combined a career in freelance curriculum development with parenthood - another important facet of education and probably the most challenging. Nancy lives in Henderson, Nevada with husband and their three teenagers.

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