Motion Chapter 1 Pages 14 31 Review Questions 3 8 10 22 24 26 28 Peer Led Team Learning PLTL ES105x CRN 21823 Looking like evening class some have requested it to start at 6 30 or 7 so they can have dinner and then go to it Day of the week still to be determined Please put your name on the sign up list if you are interested Study of Motion Aristotle 4th century BC Student of Plato Tutor of Alexander Used logic to describe natural world collected classified Motion ceased when objects in their proper place Thought speed of falling objects depended on their weight Ignored friction air resistance Influential for 2000 years Aristotle marble portrait bust Roman copy 2nd century BC of a Greek original c 325 BC in the Museo Nazionale Romano Rome Galileo Studied Copernicus work of 1543 Use experiment to test logical ideas Discovered speed not dependent on weight only on amount of time for falling http airandspace si edu etp discovery disc galileo html Galileo s Study of Motion Defined inertia keep moving in same direction and speed without outside influences resistance to change of motion Speed not dependent on weight only on amount of time for falling Noted that gravity increased speed of falling objects decrease speed of rising objects Galileo s inclined planes Balls roll down faster and faster Roll up slower and slower Weight not a factor Galileo s investigation of motion Used inclined planes to slow the descent of objects because he didn t have a precise timer Galileo s inclined planes Rises to same height as it is released Height not dependent on incline Mass Measure of inertia How much matter is there Corresponds to weight the influence of the acceleration of gravity on the mass They are proportional Mass Measured in kilograms Influence of gravity gives weight Pounds Newtons lb N On Earth 1 kg 9 8 N Not a measure of volume Inertia vs weight Weight is the force due to gravity pulling iron ball down Inertia is resistance to change of movement ball is not moving Pull slowly you increase force and break string that is holding the ball up Rapid jerk will break string below ball because it has large mass that is not moving has inertia Force Weight is a force due to gravity Force is VECTOR QUANTITY Vectors have magnitude and direction Multiple vectors add up Applied forces Objects not moving Force of weight is equal to force of string holding it up The sum of the forces is zero There is mechanical equilibrium Objects not moving In equilibrium Support Force Weight acts downward Atoms push back upward Forces equal in equilibrium Dynamic Equilibrium Can be moving At a constant speed in a straight line Net forces are zero Friction Force that acts to resist motion Always in opposite direction to applied force When you are pushing something and it moves at a constant speed the frictional force is the same as the pushing force A pair of parallel forces of 8 N and 12 N can have a resultant of 1 2 3 4 4 N 20 N Both of the above Neither of the above Explanation When parallel 12 N 8 N 20 N or 12 N 8 N 4 N Study of Motion Speed how fast Velocity how fast and what direction Acceleration how fast it is changing how fast Speed distance speed time 320km 4h 80km h Common units of speed Miles per hour mph Means miles per hour Don t use this abbreviation of the words Use mi h Kilometers per hour Meters per second km h m s Speed of cheetah 100m 4s 25m s Distance equation Rate time distance Keep units with numbers so you know you have set up the problems correctly
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