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PHYS16 – Lecture 32

PHYS16 – Lecture 32. Ch. 15 Oscillations . Oscillations pre-question. Is a bouncing ball an example of simple harmonic motion? Yes No. Oscillations pre-question.

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PHYS16 – Lecture 32

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  1. PHYS16 – Lecture 32 Ch. 15 Oscillations

  2. Oscillations pre-question • Is a bouncing ball an example of simple harmonic motion? • Yes • No

  3. Oscillations pre-question • Two kids are swinging on two swings of the same height – one kid is a little chubbier than the other. Neglecting frictional forces, which kid completes a back and forth swing in the fastest time? A) The chubby kid B) The skinny kid C) The kid who pushes off the ground the best D) Both complete in the same time

  4. Outline for Oscillations • Simple Harmonic Motion • Position, Velocity, Acceleration • Force • Energy • Resonance and Damping

  5. Oscillations and Periodic Motion Simple Harmonic Motion 1) About Equil. 2) Periodic 3) Sinusoidal http://img.tfd.com/ggse/c9/gsed_0001_0012_0_img2993.png

  6. Discussion: Examples of SHM? • Mass on a Spring • Pendulum • Snowboarder in halfpipe • Bungee jumper • Child on swing • Bobble head doll?

  7. Simple Harmonic Motion:Position, Velocity, Acceleration

  8. Simple Harmonic Motion Equilibrium Point http://www.gailruby.com/Picture4.png

  9. Discussion: Phase • Your book says that displacement is in terms of cosine and I just said that it is in terms of sine? Who is right? There is also a phase term (φ) that let’s you set the initial condition. If the oscillation starts at Ait is a sine with a φ=90 degrees or a cosine with a φ=0 degrees.

  10. SHM Position, Velocity, Acceleration http://www.tutornext.com/system/files/u89/Chapter%2011-3.gif

  11. Discussion • What is the max speed and when does it occur? Equilibrium Point

  12. Example Question • An object undergoes simple harmonic motion. If the amplitude and period are doubled, the object’s max speed is: • Quadrupled • Doubled • Unchanged • Halved • Quartered

  13. Simple Harmonic Motion:Restoring Force

  14. Restoring Force • Force that always points back to the equilibrium position – Example = spring k is just a constant – for a spring it is the spring constant http://www.cs.wright.edu/~jslater/SDTCOutreachWebsite/images/gif/spring_mass_dia.gif

  15. Restoring Force – Spring

  16. Discussion: Period • A block on a spring has a period of T. What is the period if: • the mass is doubled? • k is quadrupled? • A is doubled?

  17. Restoring Force - Pendulum • What is the period of a pendulum? http://upload.wikimedia.org/wikipedia/en/thumb/a/a8/Pendulum.png/300px-Pendulum.png

  18. Simple Harmonic Motion:Energy

  19. Energy in SHM http://www.farraguttn.com/science/milligan/APPhys/SHMOver_files/image022.jpg

  20. Main Points - SHM • Movement • Restoring Force creates oscillation • Energy is dependent on amplitude

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