Study of Motion Motion Chapter 1 Pages 14 31 Review Questions 3 8 10 22 24 26 28 Galileo Studied Copernicus work of 1543 Speed not dependent on weight only on amount of time for falling Aristotle 4th century BC Student of Plato Tutor of Alexander Motion ceased when objects in their proper Aristotle marble place portrait bust Roman copy 2nd century BC Thought speed depended on weight of a Greek original c 325 BC in the Ignored friction air resistance Museo Nazionale Romano Rome Influential for 2000 years Galileo s investigation of motion Examined motion by experiment rather than logic Used inclined planes to slow the descent of objects because he didn t have a precise timer http airandspace si edu etp discovery disc galileo html Study 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 Defined inertia keep moving in same direction and speed without outside influences resistance to change of motion Galileo s inclined planes Balls roll down faster and faster Roll up slower and slower Weight not a factor 1 Galileo s inclined planes Rises to same height as it is released Height not dependent on incline Mass Measured in kilograms Influence of gravity gives weight Pounds Newtons lb N 1 kg 9 8 N Not a measure of volume Force 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 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 Applied forces Weight is a force due to gravity Force is VECTOR QUANTITY Vectors have magnitude and direction Multiple vectors add up 2 Objects not moving 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 Support Force Dynamic Equilibrium Can be moving At a constant speed in a straight line Net forces are zero Weight acts downward Atoms push back upward 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 Study of Motion Speed how fast Velocity how fast and what direction Acceleration how fast it is changing how fast 3 Speed Common units of speed Miles per hour mph mi h Kilometers per hour km h Meters per second m s distance speed time 320km 4h 80km h Speed of cheetah 100m 4s 25m s 25m s Example of speed calculation Distance equation Rate time distance Keep units with numbers so you know you have set up the problems correctly Car traveling 60 km h for 4 h 80km 4h 320km h Notice that hours cancels because it is above and below the fraction bar 60km 4h 240km h 60 km h for 10 h 60km 10h h 600km 4 Speed and Velocity Acceleration Acceleration Change in velocity Time interval CHANGE of speed over time not the RATE of speed RATE OF CHANGE Delta Examples of acceleration is the fourth letter in the Greek alphabet Used in equations to represent change v change in velocity 45mi 20mi Driving on Monmouth Avenue at 20 mi h h h Increase to 45 mi h in 25mi 25 seconds change h in speed is 25mi h Divide change of a 1mi h s speed by time 25s 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 How to Convert to s2 25mi 1h 60 sec 1610m 11 2m s h 60 min min mi Change v to m s from mi h by using unit fractions 11 2m s m a 0 44 2 Then divide by 25s s amount of time over which the change occurs 25mi 11 2m and h s Acceleration Notice that time units appear in 25mi h 1mi h s denominator twice a 25s Because it is an amount of time over 11 2m s m which the change a 0 44 2 of speed occurs 25s s 5 Acceleration Car can go from stopped to 90 km h in 10 seconds Be sure to REDUCE to lowest terms 90km 25m hr s Acceleration 90km h 10 s 9km h s 25m s m 2 5 2 10s s Acceleration Bicycle goes from rest to 5 km h in 2 5 seconds 5km 1 39m hr s 5km h 2km h s 2 5s 1 39m s m 0 55 2 2 5s s Acceleration of Gravity Acceleration same for each second of travel Free falling objects Car goes from 60 80km 60km 20km km h to 80 km h in 10 v h h h seconds First find amount of 20km h change of speed 2km h s 10s Then divide by time 20km 5 5m hr s 5 5m s m 0 55 2 10s s Acceleration of gravity 9 81 m s2 at sea level Round off to 10 m s2 for ease of calculation unless you are trying to launch a rocket to space etc Acceleration of Gravity Free fall of object Time elapsed Speed increases seconds 10 m s for every second of fall 0 10 m s 10m 1 s s2 2 Speed meters second 0 10 20 3 30 4 40 6 Acceleration of Gravity Upward throw 30 m s Gravity acts against it Slows to stop at 10 m s2 Falls and gains speed at 10 m s2 Neglecting air resistance 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 Galileo s investigation of motion Surface area changes air resistance Objects reach terminal velocity due to air resistance In vacuum this is not a factor Hang time for basketball player Spud Webb slam dunk contest http www youtube com watch v BUu7drj9hPw He can jump 1 25 m How long is he in the air d t 1 2 gt 2 t 2d 2 1 25m 0 5s g 10m s 2 2d g to go up so double for time in the air 7
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