Sink or Float Lesson Plan

Instructor: Sharon Linde

Sharon has a Masters of Science in Mathematics

Use this lesson to teach your students about buoyancy, gravity, and density. Have students make calculations to predict buoyancy, then experiment with water.

Learning Objectives

After this lesson, students will be able to:

  • determine the density of an object
  • define buoyancy, gravity, and density
  • calculate an object's density
  • predict whether an object will float or sink


  • 1 ½ hours

Curriculum Standards

  • CCSS.ELA-Literacy.RST.6-8.3

Follow precisely a multistep procedure when carrying out experiments, taking measurements, or performing technical tasks.

  • CCSS.ELA-Literacy.RST.6-8.7

Integrate quantitative or technical information expressed in words in a text with a version of that information expressed visually (e.g., in a flowchart, diagram, model, graph, or table).

  • CCSS.ELA-Literacy.RST.6-8.8

Distinguish among facts, reasoned judgment based on research findings, and speculation in a text.


  • Several types of objects that can be weighed, measured, and put in water
  • Scales, rulers, calculators, and other tools for measuring
  • Container that holds water and is large enough for objects
  • Lab sheet with columns for 'Object,' 'Volume,' 'Mass,' 'Density,' 'Prediction,' and 'Result'


  • Watch our video lesson Predict Whether an Object Will Sink of Float: Understanding Density.
  • Pause at 3:30 for clarification. Ask:
    • What two forces impact whether or not an object floats?
    • What do we know about gravity?
    • Which is more important when determining buoyancy, gravity or buoyancy force? Why?
    • How does an object's density impact its buoyancy?
  • Play the remainder of the video.


  • Tell students they will be predicting whether or not objects will sink or float by calculating density as seen in the video.
  • Demonstrate with one object, calculating density and comparing it to the density of water. Fill out a sample lab sheet to clarify for understanding.
  • Allow students to calculate density of objects, then make predictions.
  • Circulate the room to check for understanding.
  • After all students have made calculations and predictions, share data and discuss findings.
  • Allow students to test their findings by dropping objects into water and noting the results.
  • Have students write a rule about their findings to turn in as an exit slip.


  • Have students experiment with density by increasing the mass and volume of objects, then calculating density. What happens?
  • Have students bring in items from home and repeat the experiment.

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