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Sink and Float: Science That Leaves Them Begging for More!

Printable Worksheet: sink_float_printable_Nov17 (1)

As an early childhood educator, it is always a good idea to have some engaging lessons for when the weather is too chilly or inclement to head outdoors. Exploring the idea of sinking and floating is super fun and sets a firm foundation for many science concepts that will be important as children grow older.

Background: Sinking and Floating Science

Learning what sinks and floats in water builds a strong foundation in science concepts such as: density, buoyancy and properties of matter. Although you may not use these terms with young students, their experiences exploring sinking and floating will help scaffold future learning.

Feeling shaky on your science? Although it would not be age-appropriate to present this information to Preschool or Kindergarten aged students, here is some science background to help you understand the science concepts.

An object will sink or float in water based on its density. Things that are denser than water will sink, and those less dense will float. In other words, how tightly packed are the molecules in an object? For example, imagine three containers of the same size. You’ll leave one empty, fill one half-way with golf balls, and fill the last one completely with golf balls. In this scenario the last container will be the densest because it is the most tightly packed with golf balls. It will also have the greatest mass.

Buoyancy is the upward force on an object that allows it to float. Archimedes discovered that if the weight of an object being placed in water is less than the weight of the water displaced by the object, the object will float. In other words, if you filled the bathtub with water right up to the brim, anything you put in will displace, or spill out some water. If you weigh the water that spills out and it weighs more than the object you put in, the object will float. If the spilled water weighs less than the object you put in, the object will sink. Buoyancy is why a boat floats!

Properties of matter are the characteristics of matter. This comes into play in the sinking and floating activity when students experiment with different items. For example, things that absorb water may float for a moment until they are soaked, then sink. A wooden block may float, while a sponge of the same size will eventually sink. Being porous is a property of the sponge.

Materials for Sink and Float Science Activity

This is a great activity because you can set it up fairly quickly, with materials you probably already have on hand in the classroom or at home.

You will need:
• Water source
• Large sinks, plastic bins or basins, or a water table
• Newspaper and/or towels to keep messes to a minimum
• Objects to test sinking and floating (paper clips, dice, cotton balls, sponges, toothpicks, marbles, craft sticks, paper, ping pong balls, golf balls, metal spoons, plastic spoons, etc.)
• Smocks (optional)

For Kindergarten Boat Building Extension:
• Aluminum foil
• Drinking straws
• Paper
• Tape
• Many similar sized items for weight (marbles, coins, metal washers, dice, golf balls, etc.)

Experiment with Sinking and Floating

Set up water basins on newspaper around the classroom, or give students turns around the sink. Before you begin, lay out clear directions and expectations of how students will test items before beginning. For example, you may request they only try one item at a time, or take turns in a small group.

Create a T-chart on the whiteboard or on a large sheet of paper to gather student’s predictions or hypotheses of which items will float and which will sink. Remind them that this is just their best guess, and it is okay if their prediction/hypothesis is incorrect. For young children, you may want to tape the item to the chart as well as write the word for a good visual.

Give students time to test the items. Once they have made their discoveries, bring them back into a large group.

For example: before writing “golf ball” on the chart, ask the students what they discovered. Then drop the golf ball into the basin of water so that everyone can see the result. Now you can fill in your chart. Again, you may want to tape the item to the chart as well as write the word for a good visual of the results.

Boat Building Challenge: An Extension for Kindergarten

Once they understand the concepts of sinking and floating, challenge the kids to build aluminum foil boats that hold a fixed amount of weight. In my experience, kindergartners would continue doing this activity every day for a month without tiring of it if you let them!

Set up a “boat testing” area of water basins on newspaper, or around the sink. Students should only be in this area once they have your approval to test a boat, this will reduce chaos and mess.

Give students materials like aluminum foil, paper and straws for sails (they always want to add sails!!) and some tape. Set out some items that will serve as the weight for the boat. These should be of equal weight and size.

Students will create their boats and then test to see if they float. They can draw the boat design on the “My Boat Experiment” printable before building. Once they test their boat, they can draw a picture of their experiment. If the student’s boat didn’t work the way they expected, give additional worksheets so they can re-design their boat.

If they float they can try to add some weight. How much weight can they add before it sinks? If the boat does not float, how can it be improved? Back to the drawing board! Kids love that they can engineer their own design and want to work hard to make their boat work.

Solidify Sinking and Floating Concepts

I always like to be sure that I follow up a hands-on exploration with a review of the science content. There are many children’s books that explore the concept of floating and sinking. One I’ve used in my teaching practice is Will if Float or Sink? (Rookie Read-About Science) by Melissa Stewart.


Sarah Benton Feitlinger is a science educator with over a decade of experience teaching in museums, nature centers and the science classroom. She now shares her passion for teaching science on her blog, (Share it! Science). www.shareitscience.com She loves exploring the outdoors with her family in rural New England.

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