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1/16/20078.01L IAP 2007 Last Lecture Everything you need to know about dynamics of rotation Today Pendulums and Kinetic Energy of rotation Important Concepts Equations for angular motion are mostly identical to those for linear motion with the names of the variables changed. Kinetic energy of rotation adds a new term to the same energy equation, it does not add a new equation. Kinetic energy can be simply written as a linear term and a rotational term
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1/16/20078.01L IAP 2007 Important Reminders Note that tutors have both assigned and open sessions this week. See web for schedule Mastering Physics due tomorrow at 10pm. Experiment in class on Thursday. Note that if you do NOT do the necessary calculations in advance, there is a good chance that you will NOT be able to finish the experiment in time. Problems-solving in recitation this Friday. Pset due this Friday at 4:30pm.
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1/16/20078.01L IAP 2007 Right-Hand-Rule Review (by request) Except for the gyroscope, all 8.01L problems can be solved without using R-H-R, use CW/CCW instead. However, many problems in 8.02 require R-H-R The vector for any angular quantity ( , , , , J) points along the axis with the direction given by: Fingers curl in direction of , , , , J, thumb points in the direction of the vector Cross-product Right-Hand-Rule: Fingers point along vector A, curl fingers to point along vector B, thumb points in direction C.
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1/16/20078.01L IAP 2007 Pendulums Simple pendulum: Small mass at the end of a string Period is where l is the length from the pivot to the center of the object. Physical pendulum: More complex object rotating about any pivot Period is where l is the distance from the pivot to the center of mass of the object, M is the total mass, and I is the moment of inertia around the pivot.
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1/16/20078.01L IAP 2007 Parallel Axis Theorum Very simple way to find moment of inertia for a large number of strange axis locations. I 1 = I c.m. + Md 2 where M is the total mass. d c.m. Axis 1
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1/16/20078.01L IAP 2007 Kinetic Energy with Rotation Adds a new term not a new equation! Rotation around any fixed pivot: Moving and rotating:
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1/16/20078.01L IAP 2007 Everything you need to know for Linear & Rotational Dynamics This is true for any fixed axis and for an axis through the center of mass, even if the object moves or accelerates. Rolling without slipping: Friction does NOT do work! Rolling with slipping: Friction does work, usually negative. Rarely solvable without using force and torque equations!
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