20lecture2a08

20lecture2a08 - Physics 2A Lecture 20: Feb 25 Vivek Sharma...

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Physics 2A Lecture 20: Feb 25 Vivek Sharma UCSD Physics
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E a c h i n v o l e s b d y th t r t te u t a f x What’s In Common ?
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Rotation of Rigid Bodies • Rigid body is one that is non non - - deformable deformable –relative location of all particles making up the object remain constant • All real objects are deformable so “rigid body” is an idealized model but a useful one • This week: –kinematic language to describe rotation –Kinetic Energy in rotation Dynamics of rotation
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Angular Position In Rotation • Axis of rotation passes thru center of disc & is to plane of picture • Choose a fixed reference line •P o i n t P is at a fixed distance r from the origin o i n t P will rotate about the origin in a circle of radius r
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Angular Position In Rotation Every particle on the disc undergoes circular motion about the origin, O • Polar coordinates are convenient to represent the position of P (or any other point) P is located at ( r , θ ) where r is the distance from the origin to P and θ is the measured counterclockwise from the reference line
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Change In Angular Position • As the particle moves, the only coordinate that changes is θ • As the particle moves through θ, it moves though an arc length s • The arc length and r are related: s = r
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Angular Displacement s Angular displacement = r θ is a pure number, but is given the artificial unit, n radia One radian is the angle subtended by an arc length equal to the radius of the arc o Comparing Degree and Radians: 360 1 rad = 57.3 2 r a d o π ±
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Angular Velocity ω 0 lim fi i av z f t z tt t d td t θ ω Δ Δ == −Δ Δ Δ Unit of : rad/s rpm : revs/second 2 1rpm= / 60 1 rad/s 10 rpm rad s π ±
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Angular Velocity & Right Hand Rule ω G
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20lecture2a08 - Physics 2A Lecture 20: Feb 25 Vivek Sharma...

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