1MotionChapter 1: Pages 14-31Review Questions 3-8, 10, 22, 24, 26-28Peer Led Team Learning•PLTL• ES105x• CRN 21433 • Monday or Wednesday 5:45-7:45• Library room HL 101• Teresa TrumpCourse Schedule • Note: do review question in prologue for Jan 6—not the ones in Ch 1!!Textbook website access• www.physicsplace.com• Login: GreatWOUstudent• Password: Aplus2009– Notice which letters are capital and small– No spaces in either code• I will write this inside the cover of the library copy• Or you can set up your own login and pass word with your own access codeStudy of MotionAristotle—4thcentury 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 yearsAristotle,marble portrait bust, Roman copy (2nd century BC) of a Greek original (c. 325 BC); in the MuseoNazionale Romano, RomeGalileohttp://airandspace.si.edu/etp/discovery/disc_galileo.html• Studied Copernicus’ work of 1543• Use experiment to test logical ideas• Discovered speed not dependent on weight, only on amount of time for fallingStudy 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 objectsGalileo’s inclined planes• Balls roll down faster and faster• Roll up slower and slower• Weight not a factorGalileo’s investigation of motion• Used inclined planes to slow the descent of objects, because he didn’t have a precise timer2• Rises to same height as it is released• Height not dependent on inclineGalileo’s inclined planes Mass• Measure of inertia• How much matter is there• Corresponds to weight—the influence of the acceleration of gravity on the mass• They are proportionalMass• Measured in kilograms• Influence of gravity gives weight– Pounds lb.– Newtons N• On Earth: 1 kg = 9.8 N• Not a measure of volumeInertia 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 inertiaForce• Weight is a force due to gravity •Force is VECTOR QUANTITY• Vectors have magnitude and direction• Multiple vectors add up Applied forcesObjects 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 equilibriumSupport Force• Weight acts downward• Atoms push back upward• Forces equal—in equilibrium3Dynamic Equilibrium• Can be moving• At a constant speed in a straight line• Net forces are zeroFriction• 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• Speed—how fast • Velocity—how fast and what direction• Acceleration—how fast it is changing how fastStudy of MotionSpeedtimespeeddistance==hkm4320h80kmCommon 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 km/h• Meters per second m/sHow to Convert mi./h to m/smimhhmi.1610minsec60min601.25•••smmimhhmi 2.11.1610sec60min1min601.25=•••Speed of cheetahsm4100sm25=Distance equationdistance timeRate=ו Keep units with numbers, so you know you have set up the problems correctlyExample of rt=d calculationkmhhkm320480=•• Notice that hours cancels because it is above and below the fraction bar4Car traveling• 60 km/h for 4 h• 60 km/h for 10 h=• hhkm460=• hhkm1060km240km600Speed and VelocityAccelerationintervalTimeyin velocit ChangeonAccelerati• =CHANGE of speed over time, not the RATE of speed• RATE OF CHANGEDelta Δ• Δ is the fourth letter in the Greek alphabet• Used in equations to represent change• Δv = change in velocity– Find final velocity, find initial velocity, and subtract• Δt = change in time, or time interval from beginning to end• Units of time appear twice in denominatorExamples of acceleration• Driving on Monmouth Avenue at 20 mi./h• Increase to 45 mi./h in 25 seconds—change in speed is:• Divide change of speed by time=−hmihmi .20.45smhmi 2.11.25=shmishmia ⋅== /.125/.25hmi.25244.0252.11smssm=⎟⎠⎞⎜⎝⎛Acceleration of gravity• 9.81 m/s2 at sea level• Round off to 10 m/s2for ease of calculation• …unless you are trying to launch a rocket to space,
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