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PHYS 131 student:

PHYS 131 student:. Announcements. Homework for tomorrow… (Ch. 11, Probs 10, 20, & 23) 10.76: 120 J Office hours… M 3-4 pm TWR 9-10 am F 1-2 pm Tutorial Learning Center – Houston Hall 113 MWR 8 am-6 pm T 8 am-7 pm F 8 am-5 pm.

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PHYS 131 student:

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  1. PHYS 131 student:

  2. Announcements • Homework for tomorrow… (Ch. 11, Probs 10, 20, & 23) 10.76: 120 J • Office hours… M 3-4 pm TWR 9-10 am F 1-2 pm • Tutorial Learning Center – Houston Hall 113 MWR 8 am-6 pm T 8 am-7 pm F 8 am-5 pm

  3. Chapter 11 Rotation (Relating Translational and Rotational Variables)

  4. Last time… • Rotational Position Rotating Body: • Rotational Displacement: • Rotational Velocity: • Rotational Acceleration: Kinematic Equations for Rotational Motion: s r 

  5. Demo Question The wheel rolls thru  = 2 … • How far did the center move?

  6. Quiz Question 1 A wheel initially has an angular velocity of 18 rad/s but is slowing down at a rate of 2.0 rad/s2. By the time it stops it will have turned through: • 13 rev • 26 rev • 39 rev • 52 rev • 81 rev

  7. Example The tub of a washer goes into its spin-dry cycle, starting from rest and reaching an angular speed of 5.0 rev/s in 8.0 s. At this point, the person doing the laundry opens the lid, and a safety switch turns off the washer. The tub slows to rest in 12.0 s. Through how many revolutions does the tub turn during the entire 20 s interval? Assume constant rotational acceleration while it is starting and stopping.

  8. Section 11.4: Relating Translational and Rotational Variables Can we relate angular & translational velocity? Yes! • Arc length is • Taking the time derivative • The translational speed, v, of a point on a rotating object equals the distance of that point from the axis of rotation, r, multiplied by the angular speed,  v v s  r

  9. Relationship between Translational and Rotational Acceleration Likewise… The tangential acceleration, at, of a point on a rotating object equals the distance of that point from the axis of rotation, r, multiplied by the angular acceleration, 

  10. Relations between translational and rotational quantities Summarizing…

  11. Quiz Question 2 A child riding on a playground merry-go-round rotates at a rate of 1.0 rad/s in a circle of radius 3.0 m. The translational speed of the child is: • 3.0 m/s • 0.33 m/s • 19 m/s • 0.48 m/s • 9.4 m/s

  12. Quiz Question 3 A ladybug sits at the outer edge of a record rotating at a constant 45 r.p.m. A gentleman bug sits halfway between her and the axis of rotation. Which of the following is/are true? • The ladybug’s linear speed is the same as the gentleman bug’s • The ladybug and the gentleman bug will have the same angular displacement after 1.0 s. • The ladybug and the gentleman bug have the same tangential acceleration. • I only • I & II • II &III • I, II, & III • None of these

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