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00:56 IWF (Göttingen) German 2003

Präzession eines rotierenden Rades

A spinning top (gyroscope) does not follow a torque in the same way as, for example, a top at rest. Rather, it moves sideways, it "precesses". This startling behavior will be shown here. The top is a bicycle wheel with its rim filled with lead wire. It can be suspended on a rope dangling from the ceiling. The wheel is spun while holding its axle horizontal. Then, one end of the axle is attached to the rope. The weight of the wheel and the tension in the rope together cause a torque which, however, does not turn the axle into the vertical position, as would happen if the wheel were not spinning. Instead, the axle, which indicates the direction of the wheels angular momentum, circles on a horizontal plane around the point on which it is suspended. This sideways motion of a top under the influence of a torque is called "precession".
  • Published: 2003
  • Publisher: IWF (Göttingen)
  • Language: German
01:21 IWF (Göttingen) German 2003

Dynamische Stabilität einer Fahrradkette

Belts made of soft material which are flexible while at rest, in this case a chain made of metal links, can become quite rigid, independent of their shape, when their tangential velocity is sufficiently large. This phenomenon is called "dynamic stability". Through the radial forces the chain stiffens, and after it gets thrown off the toothed wheel, it roles along the floor, jumps over a wooden beam, and collapses into its shapeless form only after coming to rest on the rug after colliding with the wall. It is clearly seen how the stiff chain deforms somewhat as it hits the beam. Note also how long the chain continues to rotate on the rug near the end of the experiment, before it finally comes to rest and collapses.
  • Published: 2003
  • Publisher: IWF (Göttingen)
  • Language: German
01:32 IWF (Göttingen) German 2003


Principle of a gyrocompass using a bicycle wheel on a rotating chair. A bicycle wheel in a fork is mounted on a chair. The fork is free to rotate around its axis which is inclined 45 degrees away from the vertical. As the chair rotates, the center of the wheel moves on a circle. The motion of its axle is observed by an experimenter on the chair, and also by a stationary observer (the movie camera). With the chair at rest, the wheel is started to spin, its angular momentum vector pointing in an arbitrary direction. When the chair is rotated, the axle of the wheel begins to oscillate. The oscillation is damped, and after a few periods, the axle of the wheel (which indicates the direction of its angular momentum) points towards the axis of rotation of the chair. When the chair is made to rotate in the opposite direction, the wheel flips 180 degrees, and after a few periods of oscillation again points towards the axis of the chair.
  • Published: 2003
  • Publisher: IWF (Göttingen)
  • Language: German
02:15 IWF (Göttingen) German 2003

Stabilisierung mit Hilfe eines Kreisels ("Einschienenbahn")

In an impressive demonstration, the precession effect is used to stabilize a very top-heavy device. A man tries to balance while sitting on a steel bar which can rotate freely around its horizontal axis. A top consisting of a lead-filled bicycle rim driven by an electric motor is attached to this bar with a joint allowing the top to be tilted away and towards the man, but not sideways. The center of mass of man and top are far above the bar. As long as the top is at rest, the man has to keep his feet on the floor to avoid tipping over. With the top spinning, pushing or pulling its axis will make the top precess, i.e. to move sideways. This motion can be used to balance the top-heavy system.
  • Published: 2003
  • Publisher: IWF (Göttingen)
  • Language: German
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