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Elf on the Science Shelf – Lego Diver and Balancing Nail Challenge

This is the third in a series of posts featuring science activities for your Elf on the Shelf. You can see the whole series here.

 Part of the fun in creating Elf on the Shelf shenanigans is bringing in your kid’s other toys to torture the elf. I’ve seen Anna and Elsa hold the elf hostage and Spiderman plaster the elf to the wall with a web. I propose flipping things around with a Lego minifig Cartesian diver.

Lego Diver
Any minifig will work here as well as most small toys that fit into a water bottle. You can see a diver made of a ketchup packet on the Go Ask Mom Easy Experiment Video. Scroll down to Cartesian Diver.


  • Water bottle full to the top of water (anything from a 16 oz to 2L soda bottle will work but it needs to be clear)
  • Lego minigure (or other small plastic toy)

Drop the minifig into the water bottle. Make sure the bottle if full to the top. The minifig will float. Squeeze the bottle hard and the minifig should sink to the bottom. If not, pull out the minifig and put a little clay or play dough on his feet to add weight.

Set out the bottle with the elf and the following note. Of course you should fill in your minifig’s name for Batman.

I’ve captured Batman! Squeeze the bottle to watch him sink. Squeezing the bottle squeezes the air bubbles in his body to make him denser than water so he sinks.

You can add some more drama by using clay to stick a small magnet on the minifig’s feet. Leave some paperclips with the elf and instructions to throw them into the bottle so that he will be stuck at the bottom forever! Of course, the elf isn’t cruel (at least at our house) so maybe using a villain minifig instead of Batman would be better.

Balancing Nail Challenge

Have your elf challenge the kids to balance all 14 nails on the head of 1 nail. This is a tricky example of center of gravity and balance.


  • 15 nails with large heads, bigger is better
  • Block of wood
  • Optional – a treat or prize for the next day if they meet the challenge

Hammer one nail into the block of wood so that it is stable but still sticks out most of the way. Set out the rest of the nails in a pile with the elf and the following note.

How good are you at balancing? See if you can get all 14 nails to balance on this 1 and I’ll have a surprise for you tomorrow!

If the kids don’t figure it out you can leave the balanced nails set up the next day (and keep the treat for yourself!). A video of the how it works is here.