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PH 211 Winter 2014

PH 211 Winter 2014. Friday January 31. Google moderator. Which topic would you like to discuss in class on Monday? http://www.google.com/moderator/#16/e=217ac5. Google moderator. Which topic would you like to discuss in class on today? http://www.google.com/moderator/#16/e=21037f.

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PH 211 Winter 2014

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  1. PH 211 Winter 2014 Friday January 31

  2. Google moderator Which topic would you like to discuss in class on Monday? http://www.google.com/moderator/#16/e=217ac5

  3. Google moderator Which topic would you like to discuss in class on today? http://www.google.com/moderator/#16/e=21037f

  4. Number of homework questions in MP. What do you think? • I would like to see more questions assigned. • I am happy with the current number. • I think there are too many questions. 0 of 208 1

  5. Cotton Ball Experiment Measure fall 2 m takes 1.2 s, a-eff = 2.7 m/s2 Measure fall 1 m takes 0.7 s, a-eff = 4.0 m/s2

  6. Cotton Ball Experiment

  7. A car goes around an upward curve (like a large hill) while maintaining a constant speed. Which of the following is the correct direction of the acceleration of the car • Upward • Zero • Forward • Downward

  8. A car goes around an upward curve (like a large hill) while maintaining a constant speed. Which of the following is the correct direction of the acceleration of the car • Upward • Zero • Forward • Downward 0 of 208 1

  9. This is the angular velocity graph of a wheel. How many revolutions does the wheel make in the first 4 s? f Slide 4-85

  10. This is the angular velocity graph of a wheel. How many revolutions does the wheel make in the first 4 s? • 2 • 4 • 6 • 8 • 10 0 of 208 1

  11. circular motion:

  12. Uniform Circular motion • KNOW: acceleration is toward center of circle • Observation: hitting a bowling ball • http://paer.rutgers.edu/pt3/experiment.php?topicid=5&exptid=56 • Observation: rollerblading • http://paer.rutgers.edu/pt3/experiment.php?topicid=5&exptid=39 • What can we hypothesize from these observations?

  13. A ball is allowed to rotate in the circular ring. What will be the motion of the ball once the board is removed? USE your hypothesis to make your prediction!! • It will continue to move in a circle • It will exit the ring moving straight with no more curve to the motion • It will exit the ring and move outwards • It will exit the ring in an arc, making a curved path that isn’t as ‘tight’ as the original circle http://paer.rutgers.edu/pt3/experiment.php?topicid=5&exptid=57

  14. A ball is allowed to rotate in the circular ring. What will be the motion of the ball once the board is removed? USE your hypothesis to make your prediction!! • It will continue to move in a circle • It will exit the ring moving straight with no more curve to the motion • It will exit the ring and move outwards • It will exit the ring in an arc, making a curved path that isn’t as ‘tight’ as the original circle 0 of 208 1

  15. Conclusions and representations • In order to accelerate, we need a force IN THE DIRECTION of the acceleration: • Force is proportional to acceleration • Force and acceleration are both represented by vectors • We know how to find acceleration from motion diagrams – there must be a (total) force in that direction • Draw a diagram WITH COORDINATE AXIS (necessary to represent a vector!) • Show the direction of the (total) force • Check if it is in the direction of acceleration

  16. ForceAcceleration Newton’s second law: All mechanics follows from this!

  17. Copernicus 1473-1543

  18. Brahe 1546-1601

  19. Kepler 1571-1630

  20. Galileo 1564-1642

  21. Andreas Cellarius: Celestial Atlas 1660

  22. Newton 1642-1727

  23. Woolsthorpe

  24. Quotations • If I have been able to see further, it was only because I stood on the shoulders of giants.Letter to Robert Hooke

  25. Quotations • I know not what I appear to the world, but to myself I seem to have been only like a boy playing on the sea-shore, and diverting myself in now and then finding a smoother pebble or a prettier shell, whilest the great ocean of truth lay all undiscovered before me.Quoted in D Brewster, Memoirs of Newton

  26. Quotations • I will not define time, space, place and motion, as being well known to all.Principia Mathematica • Truth is ever to be found in the simplicity, and not in the multiplicity and confusion of things.

  27. Units Unit of force: Newton A force of 1 N gives a mass of 1 kg an acceleration of 1 m/s2

  28. Drawing Motion Diagrams AND Free Body Diagrams for simple situations: • a hockey puck being pushed NW along a frictionless surface • a baseball mid flight (with and without drag)

  29. A car goes around an upward curve (like a large speed bump) while maintaining a constant speed. Which of the following is an accurate representation of the VERTICAL forces acting on the car? g = ground, e = earth, c = car • One • Two • Three Fgc Fgc Fgc 3 1 2 Fec Fec Fec

  30. A car goes around an upward curve (like a large speed bump) while maintaining a constant speed. Which of the following is an accurate representation of the VERTICAL forces acting on the car? g = ground, e = earth, c = car • One • Two • Three 0 of 208 1

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