Motion Chapter 1 Pages 14 31 R i Review Questions Q ti 3 8 10 22 24 26 28 click to get 9 page to print Peer Led Team Learning PLTL ES105x CRN 21220 NS 016 4 00 5 30 PM Wed Take blue sheet to registrar or show up to class this evening to decide Study of Motion Aristotle 4th century BC St Student d t off Pl Plato t 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 i ht 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 Use experiment to test logical ideas Defined inertia keep moving in same direction and speed without outside influences resistance to change g of motion http airandspace si edu etp discovery disc galileo html Galileo s Galileo s Study of Motion Discovered 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 investigation of Galileo s motion Used inclined planes to slow the descent of objects j because he didn t have a precise timer Galileo s Galileo s inclined planes Balls roll down faster and faster Roll up slower and slower Weight not a factor Galileo s Galileo s inclined planes Rises to same height as it is released Height not dependent on incline Mass How much matter is there Corresponds to weight the influence of the acceleration of gravity on the mass Mass is universal for object Object Object ss weight depends upon effect of gravity They are proportional Mass Measured in kilograms Influence of gravity gives weight Pounds lb Newtons N On Earth 1 kg g 9 8 N Measure of inertia resistance to movement Not a measure of volume Inertia vs weight g Weight is the force due to gravity pulling iron ball down Inertia is resistance to change of movement ball is not moving Pull u slowly o y you increase a force o and a d break string that is holding the ball up Rapid jerk will break string below ball because it has large mass that ball 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 F off weight i ht iis 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 F equal in l i equilibrium ilib i 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 p the frictional force is the same as the pushing force Study of Motion Speed how S d h fast f t Velocity how y fast and what direction Acceleration Acceleration how how fast it is changing velocity Speed distance speed time 320km 4h 80km h Common units of speed Miles per hour mph Means miles p per hour Don t use this abbreviation of the words Use mi h Kilometers per hour Meters M t per second d m s km h Speed of cheetah 100 00m 4s 25 5m s Distance equation Rate time distance Keep units with numbers numbers so you know o you have a e set up tthe e problems correctly Example of rt d calculation 80km 4h 320km h Notice that hours cancels because it is above and below the fraction bar Car traveling g 60 km h for 4 h 60km 4h 240km h 60 km h for 10 h 60km 10h h 600km Speed and Velocity Acceleration Change in velocity Acceleration Time interval CHANGE of speed over time time not the RATE of speed RATE OF CHANGE Delta is the fourth letter in the Greek alphabet Used in equations to represent change v change in velocity Find final velocity find initial velocity and subtract t change in time or time interval from beginning to end Units of time appear twice in denominator Acceleration of gravity 9 81 m s2 at sea level Round off to 10 m s2 for ease of calculation in lecture Use more precise value for lab calculations or if you are trying to launch a rocket to space etc Acceleration of Gravity Acceleration same for each second of travel Free falling objects Acceleration of Gravity Free fall of object Time Speed p increases 10 m s for every second of fall It goes faster over more time 10 m s 10m s s2 elapsed seconds Speed meters second 0 0 1 10 2 20 3 30 4 40 Acceleration of Gravity is downward Upward throw 30 m s Gravity acts against it Slows to stop at 10 m s2 Falls and gains speed at 10 m s 2 Neglecting g g air resistance Acceleration 25mi h a 1mi h s 25s Notice that time units appear in denominator twice Because it is an amount of time over which the change of speed occurs Does not need to be the same time units b it s but neater iff it is can change h miles l per hour into miles per second How to Convert mi mi h h to m s x mi mi 1h 1 min 1610 m 0 447 m x h 60 min 60 sec mi s Galileo s investigation of Galileo s motion Surface area changes air resistance Objects reach terminal velocity due to air resistance In vacuum this is not a factor Acceleration Neglect air resistance for these equations a v t v at acceleration is velocity divided by time velocity acquired is acceleration multiplied by time Examples of acceleration Driving on Monmouth Avenue at 10 m s Increase to 20 m s g in speed p is change Over 25 seconds divide change in speed by time 20m 10m s s 10m s 10m s 2 0 4m s a 25s Acceleration Car can go from stopped to 25 m s in 10 seconds Be sure to REDUCE to lowest terms 25m s 0m s 10 s 25m s m 2 5 2 10 s s Acceleration Car goes from 15 m s to 20 m s in 10 seconds First find amount of change of speed Then divide by time 20m 15m 5m v s s s 5m s m 0 5 10 s s Acceleration Bicycle goes from rest to 1 25 m s in 2 5 seconds 1 25m s 2 0 5m s 2 5s
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