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GVSU EGR 345 - Magnetic Damping

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Magnetic DampingTim JousmaEGR 345Lab 7aMagnetic DampingButton Magnet DropObjective: Our goal in this lab was to observe how magnetism damps motion, and tofind a damping coefficient for the magnetic interaction.Theory: Suppose a magnet crosses the path of a wire in a circuit. The field of themoving magnet will induce a voltage in the circuit. The current it sets up in the circuitwill induce a magnetic field back on the magnet. As the resistance of the circuitdecreases, the current induced will increase, because I = V/R, and the force opposing themagnet will increase. In the case of this lab, a copper tube with a certain unknownresistance replaces the circuit. A freebody diagram and the calculations for the velocity of the magnet areincluded in the accompanying mathcad document.Equipment: Computer running LabviewCopper tubeOne wire wrapped at both ends of the copper tube, and running to and between both endsOne Neodymium magnetTwo steel masses, one small, one largeCircuit Design TrainerWiresDAQ cardProcedure: Before we began the lab, the copper tube had been wrapped a both ends withone long wire. We measured the distance between the points where the wire waswrapped around the tube. We chose one magnet for our use, and found and weighed two steel masses thatwould fit down the tube with the magnet. All of the data we recorded in mathcad.In order to find the damping coefficient of the magnetic interaction between themagnet and the tube, time measurements need to be taken for two positions. Since thesemeasurements could not be taken visually, Labview was used to take measurements. Thewire wrapped around the tube was hooked up to the DAQ card so that Labview couldread the pulses from the passing magnet.In Labview, we created a virtual instrument to read waveforms from the pulses themagnet induced in the wire as it passed the wrapped wire areas. After setting up thevirtual instrument, we verified that the DAQ was working, and recorded trials withcombinations of the available weights attached to the magnet. The data from these runswas placed in Excel as voltage vs. time graphs.Data in the form of graphs is included in figures 1,2,3 & 4.Figure 1. magnet onlyFigure 2. magnet plus large masspulse v. time (magnet only)-0.06-0.04-0.0200.020.040.061163146617691106121136151166181196211226241256time (.01 sec step)voltage (V)pulse v. time (magnet plus large mass)-0.04-0.03-0.02-0.0100.010.020.031163146617691106121136151166181196211226241256time (.01 sec step)voltage (V)Figure 3. magnet plus small massFigure 4. magnet plus both massesResults: Data from four trials was taken, and four velocities and four dampingcoefficients were found. An average damping coefficient was found to be 0.415 kg/s. pulse v. time (magnet plus small mass)-0.06-0.04-0.0200.020.040.061163146617691106121136151166181196211226241time (.01 sec step)voltage (V)pulse v. time (magnet plus both masses)-0.1-0.08-0.06-0.04-0.0200.020.040.060.081163146617691106121136151166181196211226241256time (.01 sec step)voltage (V)Conclusions: We thought it odd that the relationship between mass and velocity was notperfectly linear. The data for the large mass and for the small mass each exclusivelyattached seems reversed. If these data were switched, the data would be what we wouldexpect. Still the damping coefficient would not be changed in any way.In general, it can be drawn from the graph of velocity vs. mass that the velocitydoes increase with mass. However, some undetermined error may result from that factthat the area emitting a magnetic field increases as mass of the magnet increases(assuming ferrous metals are used as additional masses). See the accompanying mathcad document for a graph of magnet velocity versus


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