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PH 211 Winter 2014 Friday January 31

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Google moderator Which topic would you like to discuss in class on Monday? ac5

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Google moderator Which topic would you like to discuss in class on today? 37f

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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.

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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

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Cotton Ball Experiment

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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

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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

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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

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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

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circular motion:

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Uniform Circular motion KNOW: acceleration is toward center of circle Observation: hitting a bowling ball – d=5&exptid=56 d=5&exptid=56 Observation: rollerblading – d=5&exptid=39 d=5&exptid=39 What can we hypothesize from these observations?

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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 isn’t as ‘tight’ as the original circle

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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 isn’t as ‘tight’ as the original circle

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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

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

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Copernicus

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Brahe

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Kepler

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Galileo

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Andreas Cellarius: Celestial Atlas 1660

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Newton

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Woolsthorpe

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

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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

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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.

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Units Unit of force: Newton A force of 1 N gives a mass of 1 kg an acceleration of 1 m/s 2

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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)

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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

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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

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