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CU-Boulder PHYS 1010 - Lecture

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8/26/20101Welcome to Physics 1010: The Physics of Everyday Life Instructor: John Bohnwww.colorado.edu/physics/phys1010Get your clickers ready!2Clickers• Everyday: swap clicker code to BA• Wait for 1stclicker question to open• Hold down On/Off Switch 4 seconds• Flashing blue light: hit B A• Type in Answer. you’re set for rest of class period• DO NOT TURN OFF CLICKER FOR CLASS (o.w. repeat above for any new clicker question)QuickTime™ and aTIFF (Uncompressed) decompressorare needed to see this picture.How did you get to class today?a) Walkedb) Rode a bikec) Took the busd) Drovee) Dropped from helicopterClicker Questiona) I have tried logging on to the homework systemb) I will try logging on this afternoonc) I absolutely promise to logon on Friday.d) none of the aboveTo do: Reading 1.1 & 1.2 (due today)Homework #1 is posted; due at 11:59 PM Friday night (TOMORROW).Important Notes on Homework: Checkboxes --- Check all that are correct!Numeric Answer --- Enter number only in box … no words or units …Units are requested in a separate box..Numeric Answer --- Either 4000 or 4.0E3. Will not recognize 4.0x10^3m/s = meters/second (not miles/second) Textbook is available on reserve in library.Phys1010 Homepage Info (www.colorado.edu/physics/phys1010) Clicker registration, Reading assignments, Homework assignmentsOffice Hours & Problem Solving SessionsPhys helproomG2B87 Phys1010 problem solving sessionin G2B87 or near by. Just look around.Enter throughG2B90Regular Weekly Hours(Starts this Thurs.)Wednesdays: 12-1 pmThursdays: 1-2 pm TODAYFridays: 12-2:30pm With John, MeganHomework too hard to do alone, butok & learn lot when work together.We will help interactions, coach,NOT give answers. cw kp8/26/20102Reading quiz. chapters 1.1 and 1.2 (read before class, learn more)1. The term “acceleration” refers toa) Motion at constant velocityb) How the distance of a moving object changes with timec) How the velocity of a moving object changes with timed) The units of velocity2) Which of the following is not accelerating?a. A parked carb. A runner just after a race beganc. An airplane that is descending to landd. A car that is shifting left to pass another car3) If two bowling balls of different weights fell off a table at the same time:a) Both would fall with the same constant velocity all the way to floor.b) The heavy ball would accelerate more rapidly.c) The light ball would accelerate more rapidly.d) Both would fall with the same acceleration.Answer: cAnswer: aAnswer: dRecall: MotionUnderstand motions around us … balls, cars, bikes, people, atoms …. But before how or why … We need to be able to describe motion… words, graphs, equations Recall: Human MotionDemo 1: Sketch distance (position) vs. time graph for 1) Person moving away from origin (motion detector) at steady velocity+0-positiontimeDo the experiment: about how fast did the cardboard move? (pick the closest value)a) 100 m/sb) 10 m/sc) 1 m/sd) 0.1 m/se) 0 m/sspeed = distance it traveledtime it tookWhat about velocity?Human MotionDemo 2: Sketch velocity vs. time graph for 1) Person moving away from origin (motion detector) at steady velocity on left. 2) Person moving toward origin (mot. det.) at steady velocity on right. Velocity+0-Velocitytime+0-timeaway towardHuman MotionDemo 2: Sketch velocity vs. time graph for 1) Person moving away from origin (motion detector) at steady velocity on left. 2) Person moving toward origin (mot. det.) at steady velocity on right. VelocityVelocity+0-time+0-timeVelocityVelocity+0-time+0-timeVelocityVelocity+0-time+0-timeVelocityVelocity+0-time+0-timeABCD8/26/20103Human MotionDemo 2: Sketch velocity vs. time graph for 1) Person moving away from origin (motion detector) at steady velocity on left. 2) Person moving toward origin (mot. det.) at steady velocity on right. Velocity+0-Velocitytime+0-time0feet10-10Velocity is a vector.Magnitude (length) gives speed. Pointing direction gives sign. (positive or negative)away towardHuman MotionDemo 2: Sketch velocity vs. time graph for 1) Person moving away from origin (motion detector) at steady velocity on left. 2) Person moving toward origin (mot. det.) at steady velocity on right. Velocity+0-Velocitytime+0-time0feet10-10Velocity is a vector.Magnitude (length) gives speed. Pointing direction gives sign. (positive or negative)What is the difference between “speed” and “velocity”? 1. You are driving 60 miles per hour north.2. You are driving 60 miles per hour. a. both give your speed, can’t tell your velocity.b. 2. gives speed, 1. gives velocity.c. both are giving your velocity.d. 2 gives velocity, 1. gives your speed.ans. b. 1. gives speed and direction = velocity. 2. gives only your speed, but since direction not specified, do not know velocity.if speed is constant 60 mph, can velocity be changing?yes! driving in circle. direction changing = velocity changing= accelerating!Human MotionDemo 3: Sketch position vs. time and velocity vs. time graphs for person moving away from origin (motion detector) at twice velocity of Demo #1 and 2.+0-PositiontimeVelocity+0-timeDescribe in words how the velocity vs time and position vs time graphs change when the speed is twice as fast.#1#1Human MotionDemo 3: Sketch position vs. time and velocity vs. time graphs for person moving away from origin (motion detector) at twice velocity of Demo #1 and 2.+0-PositiontimeVelocity+0-time#1#1+0-PositiontimeVelocity+0-time#1#1+0-PositiontimeVelocity+0-time#1#1+0-PositiontimeVelocity+0-time#1#1ADCBHuman MotionDemo 3: Sketch position vs. time and velocity vs. time graphs for person moving away from origin (motion detector) at twice velocity of Demo #1 and 2.+0-PositiontimeVelocity+0-timeDescribe in words how the velocity vs time and position vs time graphs change when the speed is twice as fast.#1#1Dvelocityman walking, web demo.8/26/20104How does position (distance) vs time relate to velocity vs time?Velocity graph is slope of position graph.1 meter0-1timevelocity+0-time2 s4 s-0.5 m/s+0.25 m/sWhat does velocity graphlook like?Velocity at 2 s is:a) 1 m/sb) -1 m/sc) 0.5 m/sd) -0.5 m/se) - 1/6 m/sVelocity (v) = change in position = distance traveledtime elapsed time it tookPosition = Starting position + change in positionPosition = Starting position + velocity x timex = xinitial+ vtEquations also help us describe and think about motionV is slope of position vs timegraph1 meter0-12 s4 stime = 1 secondposition = 1 metertime =


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