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Lecture14

# Lecture14 - PHYSICS 220 Lecture 14 Rotational Kinetic...

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Lecture 14 Purdue University, Physics 220 1 Lecture 14 Rotational Kinetic Energy and Inertia Textbook Sections 8.1 - 8.3 PHYSICS 220

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Lecture 14 Purdue University, Physics 220 2 Overview Last Lecture Center of Mass (Balance Point) Collisions and Explosions Draw “before”, “after” Define system so that F ext = 0 Set up axes Compute p total “before” Compute p total “after” Set them equal to each other Today Rotational Kinetic Energy Rotational Inertia – Torque – Equilibrium
Lecture 14 Purdue University, Physics 220 3 Rotational Kinematics Angular Linear And for a point at a distance R from the rotation axis: x = R θ v = ω R a = α R

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Lecture 14 Purdue University, Physics 220 4 Rotations: Axes and Sign When we talk about rotation, it is implied that there is a rotation “axis”. This is usually called the “z” axis (we usually omit the z subscript for simplicity). Use the right-hand rule to determine the direction of rotation. Counter-clockwise (increasing θ ) is usually called positive. Clockwise (decreasing θ ) is usually called negative. z + ω
Lecture 14 Purdue University, Physics 220 5 Rotational Kinetic Energy Consider a mass M on the end of a string being spun around in a circle with radius r and angular velocity ω Mass has speed v = ω r Mass has kinetic energy K = ½ M v 2 = ½ (M r 2 ) ω 2 Rotational Kinetic Energy is energy due to circular motion of object. M

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Lecture 14 Purdue University, Physics 220 6 You and a friend are playing on the merry-go-round at Happy Hollow Park. You stand at the outer edge of the merry-go-round and your friend stands halfway between the outer edge and the center. Assume the rotation rate of the merry-go-round is constant.
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Lecture14 - PHYSICS 220 Lecture 14 Rotational Kinetic...

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