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This report explores the oscillations of a moving magnet arranged vertically with a fixed magnet, analyzing forces, force fields, experimental setups, and results. The study includes analysis, experimental procedures, and finite damping effects.
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Problem 14Magnetic Spring Reporter: Hsieh, Tsung-Lin
Question • Two magnets are arranged on top of each other such that one of them is fixed and the other one can move vertically. • Investigate oscillations of the magnet.
Outline • Horizontal Dimension (Force field) • Experimental Setup • Experimental Result • Vertical Dimension • Analysis • Summary
Horizontal Dimension (Force field) • Experimental Setup • Experimental Result • Vertical Dimension • Analysis • Summary
Forces • Magnetic force • Gravitational force • Dissipative force
Force Field • Cylindrical magnet can be interpreted by a magnetic dipole. • When the upper magnet is at the unstable equilibrium position, the separation is said to be r0. Fig. Potential diagram for the upper magnet
Horizontal Dimension Experimental Setup • Experimental Result • Vertical Dimension • Analysis • Summary
Tube Tube Confinement • Large friction • Start with large amplitude Top view Side view
String Confinement String • Large friction • Start with large amplitude Top view Side view
Beam Confinement • Almost frictionless • Start with small amplitude
Experimental Procedures • Perturb the upper magnet • Record by camera • Change initial amplitude • Change length (l) • Change mass (m)
Horizontal Dimension • Experimental Setup Experimental Result • Vertical Dimension • Analysis • Summary
Tube Confinement • C=6.4*10-4 J-m • m=5.8 g • l=1.00 cm • y0=12.2 cm • v0=0 cm/s
String Confinement • C=5.4*10-5J-m • m=5.7 g • l=1.00 cm • y0=23 cm • v0=0 cm/s
Experimental Results • with Period • The curve at the bottom turning point is sharper • Amplitude decays • Period reduces
Beam Confinement • C=6.4*10-4J-m • l=1.00 cm • mmagnet=5.8 g • mbeam=10.0 g • Beam length=31.9 cm • y0=0.88 cm • v0=0 cm/s
Experimental Results • T=0.17 ±0.00 s • Almost frictionless • Periodic motion
Horizontal Dimension • Experimental Setup • Experimental Result Vertical Dimension • Analysis • Summary
Verifying the Equation l r l
Horizontal Dimension • Experimental Setup • Experimental Result • Vertical Dimension Analysis • Analytical • Numerical • Summary
: Moment of Inertia Equation of Motion
Small Amplitude Approximation The force can be linearized. Small oscillation period Ts =
Finite Amplitude , Thus, there are only three parameters , , .
Numerical Solution Finite oscillation period T=f (Ts, ,)
Comprehensive Solution of • y0↑,T↑ • y0→0, T→Ts • l →large,TXl 1.0 1.0 1.4 2.2
Period (T) Usage of the Solution Diagram • C=6.39*10-4 J-m • l=1.00 cm • mmagnet=5.8 g • mbeam=10.0 g • Beam length=31.9 cm • y0=0.88 cm • v0=0 cm/s
Horizontal Dimension • Experimental Setup • Experimental Result • Vertical Dimension • Analytical Modelling • Numerical Modelling Summary
Summary • Confinements • Tube • String • Beam • Analytical Modelling • Numerical Modelling 1.0 1.4
, where Thus, Small Amplitude Approximation • S.H.O., • Damping force proportional to velocity: Fig. Analytical result Fig. Tube confinement result
Finite Amplitude Damping force proportional to velocity Constant friction Both term