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Unformatted text preview: Physics 1D03  Lecture 21 Power; Rotational Energy Power Rotational work, power, and kinetic energy. Serway & Jewett 7.5, 10.4, 10.8 Physics 1D03  Lecture 21 Recall: r s = r v t = r a t = i i f t + = 2 2 2 2 2 1 + = + + = i f i i f t t Physics 1D03  Lecture 21 Power Power is the rate at which work is done: Average power = Work/time Instantaneous power: Average over an infinitesimal time dt, displacement ds ; the work is dW = F ds , and power is units: 1 J/s =1 watt (W) v F ds F = = = dt dt dW P Physics 1D03  Lecture 21 Rotational Work A bit of work, dW , is done in turning a nut through a tiny angle d : d d r F ds F dW ) sin ( ) sin ( = = = = ds F r F ds = rd d d dW = = W So, and so for a constant torque, Physics 1D03  Lecture 21 Power: dt d dt d dt dW P = = = ) ( (again, angular velocity must be expressed in radians/second)....
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 Spring '09
 MCKAY
 Physics, Energy, Kinetic Energy, Power, Work

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