# lecture30 - Angular Momentum II Angular General motion of a...

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Angular Momentum II Angular Momentum II General motion of a rigid body Collisions involving rotation Text Section 11.1-11.6

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Recall: Angular momentum” is the rotational analogue of linear momentum. m I v ϖ F τ p L (“angular momentum”) L = I α I dt dL external = = | L | = mrv t = mvr sin φ
Question Two astronauts are held together by a long rope and rotate about their common center of mass. One has twice the mass of other. One astronaut gathers in 1/3 of the rope separating them. Which of the following remain constant? A) Kinetic energy B) Angular velocity C) Angular momentum D) Tension in the rope

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) ( v r p r L m × = × = L = I ϖ. Angular momentum of a particle: of a rotating rigid body: In general, for a moving , rotating rigid body, ω v r L CM CM m I ) ( + × = The first term is called the “orbital” angular momentum and the second term is the “spin” angular momentum. Example: angular momentum of a planet about the sun.
Example: The earth (m = 6.0 x 10 24 kg, R = 6400 km) moves at speed v = 30 km/s in an orbit of radius r = 150 x 10 6 km around the sun. It also spins on its axis once per day (ω = 7.3 x 10 -5 rad/s). The angular momentum of the earth relative to the centre of the sun is

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## lecture30 - Angular Momentum II Angular General motion of a...

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