Week Twenty-Five: Buoyancy

Leave a comment

October 13, 2015 by libraryheather


Program Title:

Target Age Range: Grades 1-3

Program Length: 60 minutes

Brief Description:
Explore the science of floating and sinking with demos and activities.

2 1-cup measuring cups

1 cup dried beans

1 cup mini marshmallows

“What Floats in a Moat?” – Lynne Berry (we found this book thanks to Stir the Wonder!)

1 marble

1 small rubber ball (up to you whether it is full of air or solid like a super ball)

1 crayon

1 piece of chalk

1 clay square

1 wood square of roughly the same size as clay square

1 ping pong ball

1 golf ball

Pencils (1 per participant)

Sink or Float Prediction Sheets (1 per participant)

Clear shoebox-sized plastic storage containers for sink/float experimenting (1 per table of participants)–we got ours at the Dollar Tree, and have used them multiple times in programs

2 clear plastic containers or pitchers for sink/float demos


1 container table salt

1 orange

1 lemon

1 lime

6 rolls tin foil (or 1 box per table)–these can also be purchased at a dollar store

Pennies (we recommend ~50 per table)

Modeling clay (enough so that your participants can each make a small, cup-like boat)

A variety of sink/float items that can be used for boat building at each table (we used: LEGO bricks, cork circles, squares of styrofoam, circular scrub sponges, chalk, crayons, marbles, toothpicks, tape, and any remaining tin foil)

Multiple bath towels

Cost: $-$$ 0-100 (depending on what you have laying around that you can use!)

Advanced Preparation:

  • Test out a few tin foil boat designs at home and see how many pennies they can hold. It’s very illuminating to see which kinds work best! It will help you troubleshoot this project with the kids.
  • Put 1 cup of mini marshmallows in a 1-cup measuring cup.
  • Put 1 cup of dried beans in a 1-cup measuring cup.
  • Fill containers of water for demonstration purposes.
  • Fill a shoebox-sized clear plastic container at least halfway with water (make 1 per table).
  • Make a brick out of clay that is roughly the same size as the wood block you have.
  • Print out the Sink or Float Prediction Sheets.

Program Outline:
1. Settling in, welcome, introductions: 5 minutes

2. Explain density (be sure to include how everything is made up of molecules!) and how things float: 5 minutes

3. Read “What Floats in a Moat?” – Lynne Berry: ~5 minutes

4. Pass out Sink or Float Prediction Sheets for them to fill out, then demonstrate those objects sinking or floating: ~5 minutes

5. If something as light as a golf ball sank in water, how can something as heavy as a huge ship float? Explain how boats float: <5 minutes

6. Demonstrate how oranges, lemons and limes sink/float (and explain why!): 5 minutes

7. Floating Egg Demonstration: 5 minutes

8. Make and test out small clay boats: 10 minutes

9. Make and test out foil boats and other float/sink items: 15 minutes

Sink or Float Prediction Sheet

Special Instructions and Procedures:

  • Explain Why Things Float:
    We discussed the concept of buoyancy and water displacement here. There is a good explanation on SeaPearch.org, but you will want to break it down into simpler terms. This PDF from 21st CASP also has good explanations. The best way to figure out a simple explanation is to check out some easy reader sink/float books from the library and see what they say!
  • Sink or Float Demonstration:
    First, the children should use the Sink or Float Prediction Sheets to write in their predictions for each object–“S” for “Sink,” and “F” for “Float.” Once they’re done, hold up the first object and ask for a show of hands for who thinks it will sink, then who thinks it will float. Then, try out the object in a clear tub (or pitcher) of water. Repeat! The objects we used for this station were: a marble, a small rubber ball, a crayon, a piece of chalk, a clay block, a wood block (of same size as clay block), a ping pong ball, and a golf ball.
  • Explain Why Boats Float:
    The idea that boats can float, but something smaller and lighter (like a penny) will sink can be confusing. Use this excellent explanation from Science With Me to better understand the concept and lead a discussion about it.
  • Sink/Float Fruit Demonstration:
    It’s fun to ask kids for predictions on what will sink or float before you try out each item. The orange is so heavy, odds are they will think it’ll sink–so, be sure to explain why it can float! We did not peel the orange, but said that if we did, it would sink. Then, ask them to take a close look at the rinds of the lemon and lime and make a guess at if they will sink or float. Try it out, and then ask if anything would change if you removed the rinds. A great explanation of this phenomenon is here at Weird Science Kids.
  • Clay Boats:
    This idea came from this PDF from 21st CASP. First, we showed them how to quickly and easily shape a small boat out of clay, and asked whether it would sink or float and why (then we tested it). We reminded them of what we explained in the “why boats float” discussion. Then, they had a few minutes to try making their own small clay boats and test them out at their tables. Try to get them to make a floating shape without any weights first, but then offer up pennies to try to sink the boat (that’s the best part, after all!).

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s

%d bloggers like this: