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PHYS16 – Lecture 11

PHYS16 – Lecture 11. Ch. 6 Circular Motion. http://xkcd.com. Ch. 6 Circular Motion. Circular Motion – Definitions Tangential vs. Radial Angular position, velocity, acceleration Uniform circular motion – α =0 Uniform vs. Nonuniform Centripetal Force Solving problems with Circular Motion.

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PHYS16 – Lecture 11

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  1. PHYS16 – Lecture 11 Ch. 6 Circular Motion http://xkcd.com

  2. Ch. 6 Circular Motion • Circular Motion – Definitions • Tangential vs. Radial • Angular position, velocity, acceleration • Uniform circular motion –α=0 • Uniform vs. Nonuniform • Centripetal Force • Solving problems with Circular Motion

  3. Circular Motion pre-question • Tarzan is swinging across a lake on a vine that may not support his weight. What is the most likely point for the vine to break at? D A B C

  4. Circular Motion pre-question • An object is swung in uniform circular motion vertically. Where is the tangential acceleration the greatest? • At the top of the circle • At the bottom of the circle • At the point midway between top and bottom • At both the top and bottom of the circle • None of the above

  5. Circular Motion pre-question • A pickup has a crate of apples in its bed. The pickup makes a right turn and the once stationary crate accelerates to the left with respect to the truck bed and hits the side of the pickup. In which direction is a force acting on the crate? • To the right • To the left • Not enough information

  6. Uniform Circular Motion

  7. Uniform Circular Motion Non-uniform circular motion – both aT and aC Uniform circular motion – α =0 only centripetal accel. (aC) http://sciencefair.math.iit.edu/projects/forces/roller_coaster.jpg http://www.faqs.org/photo-dict/photofiles/list/409/2271alarm_clock.jpg

  8. Centripetal Force • Force pointing radially inward that keeps an object going in a circular path

  9. Demo – Ball on String with meter/mass

  10. Discussion Questions • If I spin a mass in a vertical circle: • Do I apply a constant force to maintain a constant linear speed? • Where is the string most likely to break? • If I spin a bucket of water in a vertical circle: • Where is the most likely spot the water will fall out? • Does the water fall out? No, gravity too. At the bottom. At the top. No, inertia.

  11. Inertial Forces • Centrifugal reaction – inertia of object causes it to stay along the same path until acted on by a force Centrifugal Reaction http://www.physicstutorials.org/images/stories/fcntrifugalimage.png

  12. Demo: Jar and Ball http://vimeo.com/11817500 http://www.youtube.com/watch?v=iRasoZMirRc&feature=player_embedded#at=73 http://www.physics.umd.edu/lecdem/services/demos/demosd1/d1-43.htm

  13. Solving Problems with Circular Motion

  14. Process of solving problems • Read the problem carefully! • Draw a picture (Trick – Free Body Diagram) • Write down the given quantities (Trick – remember Third Law) • Write down what you should solve for • Identify the eqns./concepts you should use (Trick – Second Law & separate into x/y) 6) Do the math and solve

  15. Pendulum • A bob of mass, m, swings in an arc. At angle, θ, what is the centripetalacceleration? What is the tangential acceleration?

  16. Conclusions • Angular position, velocity, and acceleration • Angular displacement vs. arc length • Angular vs. linear velocity • Angular vs. linear acceleration • Uniform circular motion –α=0 • Centripetal Force

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