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01:21 IWF (Göttingen) German 2003

Bestimmung des elektrischen Erdfeldes

The electric field of the earth will be determined. A parallel plate capacitor of area 1 m2 is attached to the end of a long bamboo pole. The capacitor is connected to a ballistic galvanometer calibrated to measure current pulses (charges). On a balcony outside the lecture hall, the capacitor is held with its plates horizontal.
  • Published: 2003
  • Publisher: IWF (Göttingen)
  • Language: German
01:59 IWF (Göttingen) German 2004

Maxwellsche Scheibe

A body that is being accelerated downward weighs less than when at rest. This is demonstrated with a flywheel on a shaft suspended on one arm of a household scale (Maxwell's disk). It is suspended on one arm of the scale with two strings which wrap around the thin shaft. When the flywheel is released, it accelerates downward, and the scale reads a reduced weight. During the subsequent rise (the flywheel still accelerating downward!) the scale again indicates a reduced weight.
  • Published: 2004
  • Publisher: IWF (Göttingen)
  • Language: German
00:54 IWF (Göttingen) German 2004

Schwanke Achse

An object rotates stably around its axis of maximum moment of inertia, even if it is attached to a bent supple shaft. The experiment also shows that particles leave a rotating object by flying off in a tangential direction.
  • Published: 2004
  • Publisher: IWF (Göttingen)
  • Language: German
01:33 IWF (Göttingen) German 2004

Induktionsläufer

Eddy currents induced in an aluminum disk in a moving inhomogeneous field tend to move the disk along with the field. This is the principle of the induction motor.
  • Published: 2004
  • Publisher: IWF (Göttingen)
  • Language: German
02:46 IWF (Göttingen) German 2004

Polarisiertes Licht

The plane of polarization of a light beam which has been polarized by passing it through a Nicol prism is made visible through scattering in a slightly milky liquid.
  • Published: 2004
  • Publisher: IWF (Göttingen)
  • Language: German
01:58 IWF (Göttingen) German 2004

Astigmatismus

The imaging error called astigmatism occurs when light travels not parallel to the axis of the lens, but under an angle. Instead of image points, extended lines or streaks are formed.
  • Published: 2004
  • Publisher: IWF (Göttingen)
  • Language: German
02:03 IWF (Göttingen) German 2003

Zur Vektornatur des Drehimpulses

A ventilator which can rotate freely around a vertical axis can be used to demonstrate that the angular momentum is a vector. A ventilator is mounted so that it can rotate freely around a vertical axis. It can also be tilted so that the air is blown either horizontally or upward. Upon turning on the ventilator, both the propeller and the driven air jet receive an angular momentum. Its vector points in the direction of the jet, parallel to the axis of the propeller. The ventilator receives an equal angular momentum in the opposite direction (opposite sense of rotation). The experiment is carried out for two different orientations of the ventilator.
  • Published: 2003
  • Publisher: IWF (Göttingen)
  • Language: German
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
02:42 IWF (Göttingen) German 2003

Drehstuhlexperimente zur Erhaltung des Drehimpulses

Conservation of angular momentum around the vertical axis of a rotating chair. A man sitting on a rotating chair with very little friction uses weights, a spinning wheel, and a wooden hammer with a long handle to demonstrate the vector nature of the angular momentum as well as its conservation in the absence of external torques. This setup allows to limit the observation to a single (the vertical) component of the angular momentum.
  • Published: 2003
  • Publisher: IWF (Göttingen)
  • Language: German
02:25 IWF (Göttingen) German 2004

Rotation um freie Achsen

It will be shown that the axis of maximum moment of inertia is also the most stable axis of free rotation. For this, objects of different shapes are suspended on thin wires from the vertical axis of an electric motor, and are rotated at increasing frequencies. They are a cylindrical metal rod, a piece of wood in the form of an egg, and a loose loop of a metal chain.
  • Published: 2004
  • Publisher: IWF (Göttingen)
  • Language: German
01:10 IWF (Göttingen) German 2004

Freie Rotation eines quaderförmigen Körpers

Only the axes of maximum and minimum moment of inertia are free axes of rotation around which a body can rotate stably without mechanical support. Attempts at rotation around other axes lead to wobbling, i.e. unstable rotation. A piece of styrofoam in the form of a parallelepiped (like a cigar box) is thrown into the air while giving it a spin. In order to watch the motion, opposing surfaces have been marked with different colors.
  • Published: 2004
  • Publisher: IWF (Göttingen)
  • Language: German
01:19 IWF (Göttingen) German 2004

Zur Physik des Turnens mit Schwüngen

Using a torsional oscillator, it will be shown how its amplitude can be increased without external torques, merely by correctly timed variations of the moment of inertia, which requires work. This is the principle of setting a swing in motion, or of swinging on the high bar. The oscillator used is a rotating stool with a helical spring. The experimenter on the stool changes the moment of inertia by alternating his position from sitting to prone.
  • Published: 2004
  • Publisher: IWF (Göttingen)
  • Language: German
01:29 IWF (Göttingen) German 2003

Freier Fall

Free fall as an example for a movement with a constant tangential acceleration.
  • Published: 2003
  • Publisher: IWF (Göttingen)
  • Language: German
01:32 IWF (Göttingen) German 2003

Kreiselkompass

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
02:38 IWF (Göttingen) German 2003

Foucaultscher Pendelversuch

A relatively simple demonstration and quantitative determination of the rotation of the earth using a simple pendulum several meters long, the so-called Foucault pendulum. The frequency of rotation can be measured in less than one minute. After carefully damping any spurious vibrations of the pendulum held at its maximum excursion, it is released using a mechanism that avoids shaking it. On the projection screen one can see how the maximum excursion of the pendulum wire shifts from one period to the next. A quantitative evaluation leads to the well known rotational frequency of the earth (1/day). Note that for this evaluation the geographic latitude has to be considered at which the experiment is being performed (f = 51.5 degrees). The actual rotational frequency of the observed rosette trace is here smaller than on the pole. On the equator, it would vanish.
  • Published: 2003
  • Publisher: IWF (Göttingen)
  • Language: German
01:44 IWF (Göttingen) German 2004

Drehpendel auf einem Karussell

A torsional pendulum on a rotating table is an instructive example of inertial forces in accelerated reference frames.
  • Published: 2004
  • Publisher: IWF (Göttingen)
  • Language: German
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