Buoyancy and density science for kids: King Arthur’s sword

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If you’ve wondered how to explain buoyancy and density science for kids, you’ll want to read on; this week we had great fun trying our own Camelot-inspired variation of this simple experiment that I found at Wonderville.

In D,8’s continuing King Arthur obsession, our version was a look at how the sword Excalibur might have floated up out of the lake to King Arthur. D had expressed some skepticism about the Lady of the Lake’s existence (but of course dragons,  magicians and evil sorcerers make perfect sense – I love how kids think!) so we used the buoyancy and density science experiment to look at how the sword might actually have floated up to the king.

density and buoyancy science for kids-king arthur's sword

You’ll need:

-two balls of clay or play dough,  the same size and weight.

-a large bowl of water.

-(optional) your King Arthur costume. This last one turns up a lot around here.

density and buoyancy science for kids-clay and bowl of water

Take one of your balls of clay and lower it into your bowl.

density and buoyancy for kids-lowering the ball of clay into the water

Watch it sink to the bottom.

density and buoyancy for kids - ball sunk at bottom of bowl

Now take your second ball of clay and shape it into a flat sword as best you can. Hollow out the middle slightly like a canoe. Lower it into the water and watch it float!
density and buoyancy science for kids-lowering the sword into the water

Once the clay sword became too soggy to use, we made a tiny toothpick sword and a smaller bowl of water and continued enjoying the ‘magic’ of the sword floating out of the water – when it breaks the surface it really is pretty thrilling!

A few other buoyancy experiments that you might want to try out:

Salt Water Density Science Experiment For Kids from Little Bins For Little Hands

Preschool Science: How Long Will A Lego Boat Float? From JDaniel4’s Mom


And, of course, you’ll want to read this week’s explorations for kids from my cohosts here at STEM Saturday!

Building Igloos with Marshmallows from Lemon Lime Adventures

Coding with LEGO from Little Bins for Little Hands

Polar Bear Science STEM Experiment from Preschool Powol Packets

Hands-on Sorting Vertebrates & Invertebrates from Stir the Wonder

10 Winter STEAM Challenges for Kids from Handmade Kids Art

10 Ice Science and Engineering Activities from The Science Kiddo


What explorations have you been up to this week?






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  1. Looks like fun!

  2. Great way to make learning fun.

  3. nice post thank you for sharing

  4. This would be perfect to play with my grand-nephew…but can we substitute an old Knights Templar outfit I still have kinking around

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