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Summer Brain Games

Experiment: Wobbler

Can you tip the teetering toad over? Why or why not? Watch as gravity and balance demonstrate equilibrium.  


Cup with rounded lid (like from a frozen coffee or slushie)
Packing tape
3 to 8 heavy washers or nuts
Craft supplies, glue, scissors (optional)  


  1. Make sure your cup is empty and clean. Remove the rounded lid, and use tape to cover the hole in the lid (where the straw goes in).
  2. Mold the clay into a ball about one inch across, or a little smaller than a ping pong ball. Place the ball of clay inside of the lid, covering the hole that is taped shut. Place the weights directly into the center of the clay. Squish them down so they’re secured tightly into the clay. If you’re using multiple washers, tape them together so they stick together.
  3. Keeping the lid upside down on a table, flip your cup over and carefully secure it into the lid. Don’t compress the plastic lid -- it needs to stay rounded and without any dents. Test it out! Gently push the wobbly cup and see if it stands back upright.
  4. If you’d like, decorate your wobbler to make it into a silly creature. You can use stickers or colored paper, or lightweight items like ribbon.

What’s Happening?  

Adding weight to the upside-down lid concentrates the mass in one spot, creating a low center of gravity. Gravity will pull the center of mass downward to the lowest possible point until the object is in equilibrium. Most of the wobbler’s mass is in the washers or quarters, and the only way for it to be in equilibrium is when the wobbler is vertical. The rounded bottom allows for the unique wobble motion as the toy reaches equilibrium.


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