Take the Sink & Float Activity Further

img_0887-1If you scroll through social media accounts, you will find a plethora of examples of folks doing sinking and floating activities with children. The popularity is expected because after all, most children love to play with water. We want to however, show you how you can deepen that activity into a core scientific idea that is important to understand: density.

Engage your child(ren) in the typical sink and float activity. First, find a variety of items in your house. Here is an example of the items we used.


  • metal spoon
  • wooden spoon
  • comb
  • rock
  • marbles
  • pin pong ball
  • wood
  • cork
  • assorted coins


You will also need a bowl and water. No expensive materials needed, rely in things already available at home!

In order to scaffold noticing a possible pattern, we used these dry erase pocket sleeves and wrote sink and float.

As the activity was happening we noticed that some objects didn’t fit right into the category and I prompted my daughter to come up with a new category. She said, “It’s in the middle”. So, we added a third dry erase pocket, it said “half-way”.


Usually an activity like this would then just turn into a conversation about why do some objects float and others sink. And if you have done this with your child already you know children’s common response is to ask, why. You may have even read a book with your child. We did too. BUT, a more in-depth study is where the gains in this fun activity lies. We proceeded to investigate the question, How can we predict whether an object will sink or float? The answer is, by comparing the objects’ density to the density of water.

Sink & Float Rules

Estimating Density

Since density is a key factor for predicting sinking or floating it is important to teach children how to figure out density. Estimating density at home can be challenging due to the lack of precise equipment but we can always try. Density can be calculated by dividing the mass of the object by the volume it displaces. We can achieve that by using an inexpensive scale and a graduated cylinder. Here is the perfect glassware set for at home experiments.

Calculating Mass & Estimating Displaced Water

Using the scale, determine the grams each object weighs. That information gives the first value for calculating density. Then, fill the graduated cylinder with water. Place the object and measure how much water is displaced. We take that difference, as the volume. Do this process for all the objects tested. Here is an example!

See the difference in the volume? Use a simple chart to record the information. This is great for children and can serve as a jump start to notice density patterns.

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Once your child has completed the chart, prompt them to check if the sinking or floating rules are observable. Compare the object’s density to the density of water (1 g/cm³). Any claims? Let us know how the lesson works out for you!






Reizelie is a parent and a Ph.D. mom trained in science education with a passion for all things STEM. She loves learning and teaching and on her spare time she helps families create home environments that foster learning. Reizelie is committed to a healthy lifestyle and shares ideas on education, cooking, urban homesteading, and fitness.

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