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Al Tobias (wat4y) - Office: Gibson S123 & Physics 218, (434) 924-0538

Physics Demo Manual

Demonstrations are cataloged according to PIRA Bibliography


Due to Physics Building renovations, the lead time to set up demo requests has increased due to the need to transport equipment across campus. Please be kind and let me know well ahead of time what you need.

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 Motion In One Dimension
 Motion In Two Dimensions
 Newton's First Law
 Newton's Second Law
 Newton's Third Law
 Statics Of Rigid Bodies
  video  - Center of Mass of Virginia
  video  - Center of Mass Toys
 Stacking Blocks
  video  - Stability Track
  photos  - Tension in a String
 Rope and Three Students
  photos  - Knot in Static Equilibrium
 Force and Tension
 The Roman Arch
 Rotational Equilibrium
  video  - Giant Yo-Yo
 Applications Of Newton's Laws
 Work and Energy
 Rotational Motion
 Properties of Matter

 video  - Center of Mass Toys


To illustrate the concept of center of mass.


centered image

Various aspects of center of mass can be demonstrated through creative use of the toys (pictured below).

  1. Balancing Spoon & Fork with Match Stick: can be used with a cup
  2. Tiltable Prism: with plumb bob falling within area of its base, the prism stands; if not, the prism falls
  3. Tightrope Mickey Mouse: with long downward bending pole with masses on either end lowers Mickey's center of mass to below the rope establishing a stable equilibrium in addition to increasing his moment of inertia
  4. Double Cone rolling up the incline: seems to roll uphill, but actually rolls toward diverging rails
  5. Balancing Horse: with the center of mass below its feet
  6. Leaning Tower of Pisa: is unstable with top in place and stable with top removed
  7. Semi Circle with adjustable ball mass: system stable with ball at bottom of support rod
  8. Balancing Bird: with the center of mass at the tip of its beak


Try balancing a soda can at 45-deg angle that is full, partially full and empty. You'll find that a stable equilibrium is achieved with a can about 1/3 full.


  • Center of Mass Toys