MotionChapter 1: Pages 14-31Review Questions 3-8, 10, 22, 24, 26-28Peer 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 interestedStudy 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 fallingGalileo'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 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 timer• Rises to same height as it is released• Height not dependent on inclineGalileo’s inclined planesMass• 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 upApplied 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 equilibriumObjects not moving• In equilibriumSupport Force• Weight acts downward• Atoms push back upward• Forces equal—in equilibriumDynamic 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 forceA pair of parallel forces of 8 N and 12 N can have a resultant of• Explanation:When parallel, 12 N + 8 N = 20 N, or 12 N – 8 N = 4 N.1. 4 N.2. 20 N.3. Both of the above.4. Neither of the above.• 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/sSpeed of cheetahsm4100sm25=Distance equationdistance timeRate=ו Keep units with numbers, so you know you have set up the problems
View Full Document
Unlocking...