Phys Lab 8

Phys Lab 8 - Properties of a Torsion Pendulum John Domanick...

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Properties of a Torsion Pendulum John Domanick 11/16/10 Partner: Matt Wiener Teaching Fellow: Tim Harden
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Abstract:
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In this experiment we observed the simple harmonic motion of a torsion pendulum, and intrinsic properties of the pendulum such as the torsion constant and moment of inertia. This torsion pendulum resembles closely the motion of a bouncing mass on a spring or bungie cord, and the ballistic pendulum used in previous labs. After investigating the angular displacements of the pendulum caused by various masses, we found the torsion constant of the pendulum to be 0.00156+/-3.03x10 -5 N*m/rad. We also investigated the moments of inertia for various masses on the pendulum. For each mass we found that both our experimental values and theoretical values agreed within uncertainties. Theory: When a torsion pendulum is rotated from its original equilibrium position, a restoring force generates a torque on the pendulum, to return to equilibrium. This motion is a simple harmonic motion for small angular displacements. Torque is equal to the change in angular momentum over time: For our pendulum we can measure the torque for varying angular displacements by using known masses strung over a pulley. By calculating the force of gravity, which is equal to the tension of the string, and equal to the force of the pendulum restoring force, we can calculate the torque as: where, r is the moment arm of the force, which is equal to the radius of the pendulum. Much like the restoring force of a spring, the restoring torque of our pendulum is related to the displacement from equilibrium by a constant, κ , the torsion constant. We can find this torsion constant by plotting torque vs. angular displacement and finding
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This note was uploaded on 10/06/2011 for the course PHYS 19 taught by Professor Blocker during the Fall '10 term at Brandeis.

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Phys Lab 8 - Properties of a Torsion Pendulum John Domanick...

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