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PHYWE Oscillations Pohl's Pendulum |
Learn about ...
- Angular frequency
- Characteristic frequency
- Resonance frequency
- Torsion pendulum
- Torsional vibration
- Torque
- Testoring torque
- Damped/undamped free oscillation
- Forced oscillation
- Ratio of attenuation/decrement
- Damping constant
- Logarithmic decrement
- Aperiodic case
- Creeping
If an oscillating system is allowed to swing freely, it is observed that the decrease of successive maximum amplitudes is highly dependent on the damping. If the oscillating system is stimulated to swing by an external periodic torque, you can observe that in the steady state the amplitude is a function of the frequency and the amplitude of the external periodic torque and of the damping. The characteristic frequencies of the free oscillation, as well as the resonance curves of the forced oscillation for different damping values, can be determined.
To determine the characteristic frequency of the torsion pendulum without damping, the time for several oscillations is measured repeatedly and the mean value of the period calculated. In the same way the characteristic frequencies for the damped oscillations are found using specific current intensities for the eddy current brake. To determine the damping values the decrease in amplitude is measured by deflecting the pendulum completely to one side while observing the magnitude of successive amplitudes on the other side. Initially it has to be ensured that the pendulum pointer at rest coincides with the zero-position of the scale. This can be achieved by turning the eccentric disc of the motor.
To realize the aperiodic case and the creeping case the eddy current brake is briefly connected directly to the DC output of the power supply unit. To stimulate the torsion pendulum, the connecting rod of the motor is fixed to the upper third of the stimulating source. The DC voltage of the power supply unit must be set to maximum. The stimulating frequency, ?a, of the motor can be found by using a stopwatch and counting the number of turns. The measurement begins with small frequencies. ?a is increased by means of the motor-potentiometer setting “coarse.” In the vincinity of the maximum a is changed in small steps using the potentiometer setting “fine.” In each case, readings should only be taken after stable pendulum amplitude has been established. In the absence of damping or for only very small damping values, ?a must be chosen in such a way that the pendulum does not exceed its scale range.
With this experiment, you can determine the oscillating period and the characteristic frequency of the undamped case. The oscillating periods and the corresponding characteristic frequencies for different damping values can be determined. Successive, unidirectional maximum amplitudes can be plotted as a function of time. The corresponding ratios of attenuation, the damping constants and the logarithmic decrements will also be calculated.
For forced oscillation the resonance curves can be determined and to be represented graphically using the damping values of A. The resonance frequencies can be determined and compared with the resonance frequency values found beforehand. The phase shifting between the torsion pendulum and the stimulating external torque can be observed for a small damping value assuming that in one case the stimulating frequency is far below the resonance frequency and in the other case it is far above it.
For WLS1807-83 the oscillations are recorded with the Cobra3 system in connection with the movement sensor. The curves of the different oscillations are displayed and the necessary quantities for the determination of the characteristic values can easily be calculated.
Included with WLS1807-82:
Torsion pendulum after Pohl; universal power supply; bridge rectifier, 30 V AC/1 A DC; digital stopwatch, 1/100 sec.; digital multimeter; connecting cords; and manual.
Included with WLS1807-83:
Torsion pendulum after Pohl; universal power supply; bridge rectifier, 30 V AC/1 A DC; digital stopwatch, 1/100 sec; digital multimeter; connecting cords; Cobra3 Basic Unit; power supply, 12 V; RS 232 data cable; Cobra3 Translation/Rotation Software; movement sensor with cable; adapter, BNC-socket/4mm plug pair; adapter, BNC-socket-plug, 4 mm; silk thread, l = 200 m; weight holder, 1 g ; tripod base; support rods; right angle clamp; and manual on CD-ROM.
System requirements for WLS1807-83:
PC, WindowsR 95 or higher
For your convenience this experiment is available to you as a complete set.
Everything you require to perform the activities are included in the total price.
For assistance in using your new equipment we also offer professional development (WLS1808-24) on all PHYWE line products.
For customization options and pricing please contact your local Cenco representative.
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