Bulletin 4H1750
Teaching science when you don’t know diddly-squat: Why do some things float and others sink?


October 23, 2017 -


The purpose is not to teach specific content, but to teach the process of science – asking questions and discovering answers. This activity encourages young people to try to figure things out for themselves rather than just read an answer on the internet or in a book. As a leader, try not to express your opinion, but let the youth engage in arguments based on evidence.

Time required

20 minutes or multiple days depending on the interest and questions the youth have


  • Golf ball and pingpong ball (or any two objects that are roughly the same size, where one sinks and one floats)
  • Bucket, basin or bowl (something that will hold water)
  • Water
  • Other items that might float or sink

Science Practice:

Asking questions and defining problems

1. Why do some things float and others sink? Have them share their answers. Don’t share your ideas. After they have given answers, follow up with more questions. 

Science Practice:

Planning and carrying out investigations

2. Do things that are the same size weigh the same? Why or why not?

3. Give a youth a golf ball and pingpong ball. Ask the group:

a. Which weighs more or feels heavier?

b. Which is bigger or has a greater volume?

4. Ask the group: Do you think the balls will sink or float in water? Why?

5. Drop each ball into a bucket of water. What happened?

a. Density (Density=mass/volume) describes the relationship between mass (weight) and volume (space something takes up). What statement can you make about density and the two balls you just dropped in the water?

Science Practice:

Constructing explanations and designing solutions

6. Why did the golf ball sink and the pingpong ball float? Are there other things that are the same size and one might sink and one might float?

Science Practice:

Engaging in argument from evidence

7. Gather other items that you think might or might not float. Predict whether each item will sink or float, then test them. Can you accurately predict what will sink and what will float? Why or why not?

Other thoughts:

  • Do you think there are solid items that might float?
  • Does the weight of an object affect whether it floats?
  • What would it take to sink a pool noodle? A balloon? Beach balls?
  • Is there anything that is too heavy to float? Is there anything too light to sink?
  • Why does a boat float until you poke holes in it?
  • Why do huge metal boats still float?

Science & Engineering Practices:

These eight Science and Engineering Practices come from A Framework for K–12 Science Education (National Research Council, 2012, p. 42). These research-based best practices for engaging youth in science are connected to in-school science standards that all children must meet.

  • Asking questions and defining problems
  • Developing and using models
  • Planning and carrying out investigation
  • Analyzing and interpreting data
  • Using mathematics and computational thinking
  • Constructing explanations and designing solutions
  • Engaging in argument from evidence
  • Obtaining, evaluating, and communicating information


National Research Council. (2012). A framework for K-12 science education: Practices, crosscutting concepts, and core ideas. Washington, DC: National Academies Press


Accessibility Questions:

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