29lecture2a08

# 29lecture2a08 - PL. Turn Off Your Cell Phone Now ! Physics...

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PL. Turn Off Your Cell Phone Now !

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Physics 2A Lecture 29: Mar 13 Vivek Sharma UCSD Physics
Pivoted Rod As A Physical Pendulum L Uniform rod length L, pivoted at one end, T=? 2 Moment of Inertia about an axis 1 thru one end of rod, I= 3 ML CG 2 1 3 22 /2 ML I T Mgd mgL ππ == 2 2 3 phys L T g π = 2 3 rod rod physical simple TT ⇒= for uniform rod is at d=L/2 CG

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Period of Physical Pendulum: About Different Axis of Rotation Distance between rotation axis and center of mass is L /2 Distance between rotation axis & center of mass is x .
Modeling T. Rex’s Walk When you are walking, leg (idealized as rod) not in contact with ground, swings and acts as a physical pendulum How fast did T-Rex walk based on footprint & legsize ? Leg len Assume gth L=3 Uniform densit .1m Stride leng y leg b th S one =4.0m

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Modeling T. Rex’s Walk leg 2L Oscillation Period T=2 3g For L=3.1m T 2.9 s π ⇒= leg Distance moved=S in time T 4.0 1.4 / 2.9 Same velocity as human beings ! Tr e x m vm s s =
Hollywood Did Not Take 2A ! Likely T-rex could not have chased jeeps with v=70km/h as portrayed in Jurassic Park ….. go tell Spielberg that !

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The Chicken Vs T-Rex Sprint ! Each period T corresponds to complete back & forth swing of leg= 2 steps 2 Walking pace = steps/time = 2 T f = 13 1 22 Chicken with smaller L has much larger walking pace!
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## This note was uploaded on 05/08/2008 for the course PHYS 2A taught by Professor Hicks during the Winter '07 term at UCSD.

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29lecture2a08 - PL. Turn Off Your Cell Phone Now ! Physics...

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