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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
 Ladder Against a Wall
 Walking the Giant YoYo
 Weight Dependence of Friction
  video  - Contact Area Independence of Friction
 Coefficient of Friction
 Work and Energy
 Rotational Motion
 Properties of Matter

Walking the Giant YoYo


A non-intuitive demonstration of dynamic torque acting on a rigid body.


By pulling on the string, the yo-yo can be forced to roll either towards or away from you. The direction that the yo-yo rolls depends on the angle the string makes with the vertical as well as the relative size of the axle of the yo-yo (see figure). This can be seen easily by looking at the torques about the point of contact between the yo-yo and the floor. If a force is applied to the string such that the string makes an angle theta with the vertical axis as shown below, there is no net torque about the point of contact so the yo-yo will not roll. If the string is pulled such that the angle it makes with the vertical is less than theta, there will be a net torque out of the picture and the yo-yo will move to the left. Increasing the angle so it is greater than theta will cause the yo-yo to move to the right. The critical angle can be found experimentally by applying a constant tension to the string and allowing the yo-yo to come to rest.


For the yo-yo in the picture:

r = 4.3 cm
R = 12.3 cm