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Sink or Float?

Sink or Float is one of my favorite science activities.  Water activities are always a hit.  The idea of making a prediction and conducting a scientific experiment.  The children experience weight, density, and buoyancy in the comfort of the classroom or home.  The set up is so simple, and it can be changed with seasons, unit studies, or themes.
sink or float

  • waterproof signs that read “sink”  and “float”
  • even amounts of water-safe items that either sink or float
  • a container full of water
  • a tool for fishing out the objects
  • towel or sponge for drying objects

When given the opportunity to test out many objects, children will start to make connections between weight and the outcome of each object.  They will begin to notice if the material (wood, plastic, rubber, metal) of the object has something to do with sinking or floating.  After time, they may notice the water level rise when testing more dense items.

working sink or float

I like to take this activity outside in the warm weather, to allow for full exploration with toddlers.  Water tables and bathtubs are wonderful for Sink or Float, too.  In the classroom, all items are on a big tray, to avoid floods.  When putting this activity together, be sure to test the items yourself.  I was so surprised, I predicted the wrong outcome a few times.

After working with Sink or Float, I love reading the Rookie Read About Book, Will It Float or Sink?

Roll up your sleeves and make some discoveries!


Written by Jessie Beerman, M. Ed, from The Education of Ours,

a blog about Montessori Education for the home.

Jessie is a proud mom to three daughters, and a Montessori Teacher

who dabbles in writing, art, and yoga.


Activity of the Week – Sink and Float Plus Extensions |

Monday 20th of June 2011

[...] has a post at Mommy Moment with directions for using sink and float indoors or outdoors. There’s also the helpful idea of [...]

Alicia C.

Wednesday 20th of April 2011

I loved doing this when I was a kid and my oldest still enjoys trying different things out to see if they'll sink or float. I can't wait until it gets warm enough for my little guy to do this outside this summer!


Monday 18th of April 2011

I gave you an award here

Lori@montessori MOMents

Monday 18th of April 2011

We LOVE the sink or float experiment in our home! It's always a hit. I love that you added the waterproof "sink" and "float" signs. We did a nature walk and did a float or sink experiment with all of the things we found on our walk. The boys really loved it. Here's the link to our experiment:

I love your posts Jessie! Thanks for inspiring us.

Deb @ Living Montessori Now

Sunday 17th of April 2011

Great post, Jessie! Sink and Float was always one of my favorite science activities, too! I love your idea of having waterproof signs. It was interesting that one year my daughter's Iowa Basics test (required for homeschooling in our state) had a question about objects that sink and float. My daughter didn't have to think at all to know the answer to that question! :)