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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
 Applications Of Newton's Laws
 Work and Energy
 Rotational Motion
 Rotational Inertia Rods
  video  - Rolling Objects and Moments of Inertia
  video  - Moment of Inertia Wheel
  video  - The Falling Rigid Body
  video  - Vector Nature of Angular Momentum
 Hero's engine
  video  - Precession of Bicycle Wheel Under Gravity Force
 Suitcase Gyro
 Air Gyro
 Euler's Disk
 Tippe Top
 Properties of Matter

 video  - Rolling Objects and Moments of Inertia


To show objects that have different moments of inertia accelerate at different rates when rolling down an inclined plane.


centered image

Roll different objects down the incline in race fashion, starting them with the meter stick. Interpret results in terms of moments of inertia. For example:
  • Solid cylinders of different mass and radius roll down the incline at the same rate & reach the bottom at the same time.
  • Objects of equal mass and radius but different shape or solid/hollow will roll down the incline at different rates. Solid sphere is faster than solid cylinder since sphere has lower moment of inertia, higher translational kinetic energy. Hollow object is slower than equivalent solid object.
  • Objects of same dimension but different mass will reach the bottom at the same time.
Four major "pre-packaged" demos are available:
  1. Two objects with the same mass but different mass distribution roll differently.
  2. Two object of different mass but similar outer shape can roll quite differently. The lighter shell rolls slower than a heavier solid cylinder demonstrating that the R2 "wins" over the mass term.
  3. Two objects of different masses and different shapes can roll quite similarly (not quite).
  4. Two objects with similar geometrical mass distribution (2 different solid cylinders or 2 different hollow cylinder) roll independently of the radius or mass. The time of descend only depends on the "geometrical multiplier coefficient" k, I=kmR2.


  • Meter Stick
  • Inclined Plane
  • Rolling Moment of Inertia objects