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Torsional Oscillator

Apparatus

There are a few apparatus pieces you’ll need in order to make these damping measurements.

Linear Damping (v^0)

You will use some strings tied across the rotor to add a constant friction force.  See Figure 3.0 in the TeachSpin Manual and Figure 2 below.

damping with string
Figure 3: A string tied to the apparatus that rubs on the rotor, causing friction.

Typical Damping (v^1)

To achieve the easily-modelled v^1 damping, you will engage two magnet stacks on either side of the apparatus.  As the copper disk moves through the magnetic field, eddy currents develop in the copper which acts as a drag force proportional to the velocity of the copper disk.  The knobs on either side of the apparatus move the magnet stacks by 1/20 of an inch (about 1.27 mm) with every turn. Figure 4 shows the magnetic dampers barely overlapping the copper disk.

magnetic damping
Figure 4: Magnetic dampers, used to cause v^1 damping, barely overlapping the copper disk

Fluid Damping (v^2)

Fluid damping is achieved using very light and VERY fragile paddles that are mounted into the rotor.  Please ask the TA or technician to discuss how to use the paddles in a way that won’t damage them.  The paddles drag the air around them as the rotor turns, which is an important factor at relatively high velocity, but negligible when the rotor is turning slowly.  The paddles are shown in Figure 5.

paddle damping
Figure 5: Paddles used to introduce fluid-based friction to the torsional oscillator.

Chapter 6.1 in the TeachSpin manual contains dimensions and masses of the various components.

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Physics 3P03 Lab Manual Copyright © by Daniel FitzGreen. All Rights Reserved.

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