Lecture13 - PHYSICS 149: Lecture 13 Chapter 5: Circular...

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PHYSICS 149: Lecture 13 • Chapter 5: Circular Motion – 5.1 Description of Uniform Circular Motion – 5.2 Radial Acceleration – 5.3 Banked and Unbanked Curve – 5.4 Circular Orbits of Satellites and Planets Lecture 13 Purdue University, Physics 149 1
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ILQ 1 hen an elevator accelerates upwards, your When an elevator accelerates upwards, your apparent weight A) increases. B) stays the same. C) decreases. Lecture 13 Purdue University, Physics 149 2
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ILQ 2 Amy and Bob release their snowballs from the same height and at the same time. Amy's is dropped while Bob‘s is thrown horizontally. Which one hits the ground first? A) the "dropped" snowball B) the "thrown" snowball C) they hit at the same time D) it depends on the initial height Lecture 13 Purdue University, Physics 149 3
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ILQ 3 A ball is thrown into the air and follows a parabolic ajectory nore air resistance t the highest trajectory. Ignore air resistance. At the highest point in the trajectory, A) the acceleration is zero, but the velocity is not zero. B) the velocity is zero, but the acceleration is not zero. C) both the velocity and the acceleration are zero. D) neither the acceleration nor the velocity are zero. x-component: constant velocity motion Lecture 13 Purdue University, Physics 149 4 y-component: constant acceleration motion
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Examples of Circular Motion Lecture 13 Purdue University, Physics 149 5
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Angular Variables • The motion of objects moving in circular (or nearly ircular) paths is often described by angles measured in circular) paths, is often described by angles measured in radians rather than degrees. he angle radians, is defined as: The angle θ in radians, is defined as: s θ= r • If s = r the angle is 1 rad • If s = 2 π r (the circumference of the circle) the angle is d n other words 60 ° d Lecture 13 Purdue University, Physics 149 6 2 π rad. (In other words, 360 = 2 π rad .)
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Example • If a radius is 2 m and an arc length is 100 cm, what is the angle subtended by the arc? θ = s / r = 100 cm / 2 m = 1 m / 2 m = 0.5 rad ince 2 d = 360 ° Since 2 π rad = 360 , 1 rad = (360/2 π ) ° Thus, θ = 0.5 rad = 0.5 × (360/2 π ) ° = 28.65 ° Lecture 13 7 Purdue University, Physics 149
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Circular Motion • Angular displacement ∆θ = θ 2 - θ 1 – How far it has rotated nits: d or ° Units: rad or • Angular velocity ω = ∆θ / t – How fast it is rotating – Units: radians/second (2 π = 1 revolution) eriod = 1/frequency • Period = 1/frequency – T = 1/f = 2 π / ω Lecture 13 Purdue University, Physics 149 8 – Time to complete 1 revolution
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ILQ A CD makes one complete revolution every tenth of a second. The angular velocity of point 4 is: A) the same as for pt 1. B) twice that of pt 2. C) half that of pt 2. D) 1/4 that of pt 1. E) four times that of pt 1. Lecture 13 9 Purdue University, Physics 149
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Circular to Linear •D i s placement s = r ∆θ ( θ in radians) • Speed |v| = s/ t = r ∆θ / t = r ω | = 2 |v| = 2 π rf |v| = 2 π r/T • Direction of v is tangent to circle Another way to express v is by using the relation between period and speed |v| = 2 π r/T Lecture 13 Purdue University, Physics 149 10
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ILQ
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This note was uploaded on 04/23/2011 for the course PHYS 149 taught by Professor Staff during the Spring '08 term at Purdue University-West Lafayette.

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Lecture13 - PHYSICS 149: Lecture 13 Chapter 5: Circular...

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