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Slide 2 PH 211 Winter 2014 Friday January 31 Slide 3 Google moderator Which topic would you like to discuss in class on Monday? http://www.google.com/moderator/#16/e=217 ac5 Slide 4 Google moderator Which topic would you like to discuss in class on today? http://www.google.com/moderator/#16/e=210 37f Slide 5 Number of homework questions in MP. What do you think? A.I would like to see more questions assigned. B.I am happy with the current number. C.I think there are too many questions. Slide 6 Cotton Ball Experiment Measure fall 2 m takes 1.2 s, a-eff = 2.7 m/s 2 Measure fall 1 m takes 0.7 s, a-eff = 4.0 m/s 2 Slide 7 Cotton Ball Experiment Slide 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 1.Upward 2.Zero 3.Forward 4.Downward Slide 9 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 A.Upward B.Zero C.Forward D.Downward Slide 10 This is the angular velocity graph of a wheel. How many revolutions does the wheel make in the first 4 s? Slide 4-85 f Slide 11 This is the angular velocity graph of a wheel. How many revolutions does the wheel make in the first 4 s? A.2 B.4 C.6 D.8 E.10 Slide 12 circular motion: Slide 13 Uniform Circular motion KNOW: acceleration is toward center of circle Observation: hitting a bowling ball http://paer.rutgers.edu/pt3/experiment.php?topici d=5&exptid=56 http://paer.rutgers.edu/pt3/experiment.php?topici d=5&exptid=56 Observation: rollerblading http://paer.rutgers.edu/pt3/experiment.php?topici d=5&exptid=39 http://paer.rutgers.edu/pt3/experiment.php?topici d=5&exptid=39 What can we hypothesize from these observations? Slide 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!! 1.It will continue to move in a circle 2.It will exit the ring moving straight with no more curve to the motion 3.It will exit the ring and move outwards 4.It will exit the ring in an arc, making a curved path that isnt as tight as the original circle http://paer.rutgers.edu/pt3/experiment.php?topicid=5&exptid=57 Slide 15 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!! A.It will continue to move in a circle B.It will exit the ring moving straight with no more curve to the motion C.It will exit the ring and move outwards D.It will exit the ring in an arc, making a curved path that isnt as tight as the original circle Slide 16 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 Slide 17 Force Acceleration Newtons second law: All mechanics follows from this! Slide 18 Copernicus 1473-1543 Slide 19 Brahe 1546-1601 Slide 20 Kepler 1571-1630 Slide 21 Galileo 1564-1642 Slide 22 Andreas Cellarius: Celestial Atlas 1660 Slide 23 Newton 1642-1727 Slide 24 Woolsthorpe Slide 25 Quotations If I have been able to see further, it was only because I stood on the shoulders of giants. Letter to Robert Hooke Slide 26 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 Slide 27 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. Slide 28 Units Unit of force: Newton A force of 1 N gives a mass of 1 kg an acceleration of 1 m/s 2 Slide 29 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) Slide 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 1.One 2.Two 3.Three F gc F ec 1 F gc F ec 2 F gc F ec 3 Slide 31 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 A.One B.Two C.Three