Mobile Activity: Finding the Center of GRavity in Real Life


Create a balanced mobile (in equilibrium) using the principles of center of gravity.


  • String to hang
  • Beams (to hang objects on)
    • Popsicle sticks
    • Hot glue
  • Hanging objects
    • Wire for attaching
    • Pom-poms
    • Stones
    • Beads
    • Any object you bring in or make to hang on the mobile!
  • Ruler and scale for measurements
  • Your name(s) must be on the bottom beam.


You may work by yourself or with one other person in this class.

Mobile Requirements:

2beams picture

  • Due to limited ceiling space, it must be less than 0.75 long as measured from the top beam down to the bottom of the lowest hanging object.
  • Must have at least 3 beams
  • Each beam must have objects hanging from at least 3 different positions
  • Hanging objects should be an arrangement of multiple items (ex. 1 bead is not acceptable)
  • Hanging arrangements on each beam should be different masses and positions
  • Mobile must be balanced according to center of gravity calculations
  • Neatly written and organized calculations for COG of each beam must be turned in with mobile
  • Mobile is nicely built and has a design theme. 


It will be built in class. You are to bring everything to class on the designated date. You may pre-decorate if you choose.


  • Build the bottom beam first.
  • Build beams first and measure their mass.  Find center of gravity of beam alone by balancing on finger.
  • Make hanging object arrangements and measure mass including hanging wire, then hang from beam.
  • You will need to estimate the center of gravity for each hanging object, using symmetry helps!
  • Attach hanging objects where you want, then calculate COG – that is where you would attach the string for hanging the beam.

Grading Rubric



Below Expectations
(< 50%)

Meets Expectations
(50% - 90%)

Exceeds Expectations (> 90%)



Lacks balance, or does not follow calculations

Each beam is balanced according to COG calculations

Perfectly balanced and stable using exact calculations

Beam Requirements


< 2 beams

2 beams

> 2 beams

Hanging Object Requirements


< 2 hanging objects, or didn’t use different mass and placement

2 hanging objects from each beam, different mass and placement

> 2 hanging objects and greatly varied mass and placement



Mobile is messy and lacking design

Mobile is neat, creative, and pleasing to the eye

Mobile is very neat with a creative design theme



Unorganized, missing work, or incorrect

Neat, organized, shows all data and work, and correct

Very organized, showing all work, includes diagrams, data table, and is correct

       TOTAL             /20

I wish I could keep all of the mobiles up in my room all year long, but space is limited. The top three, as voted on by the class, will be requested to be kept up for the rest of the year. If you want to take them home you may. It's your hard work.


by Tony Wayne ...(If you are a teacher, please feel free to use these resources in your teaching.)

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