3Observing Motion Motion An object’s change in position relative to a reference pointWhen an object changes position with respect to a frame of reference, the object is in motion.north, south, east, west, up, or down
4Group Questions Slide 1A person sits in the passenger seat of a car that is traveling down a street. Describe the person as seen by each of the following observers:A person sitting in the backseat of the carA person standing on the sidewalk as the car passesThe driver of a second car moving in the same direction and passing the first car
5Group Questions Slide 2A person stands near a bus stop. Describe the standing person’s motion as seen by the following observers:A person sitting in an approaching busA person riding in a car moving away from the bus stopAnother person standing at the bus stop
6DiscussionDo any observers say that the person sitting in the passenger seat of the car in the first slide was moving? ExplainDo any observers say that the person sitting in the passenger seat of the car in the first slide was not moving? ExplainDo any observers say that the person standing near the bus stop in the second slide was moving? ExplainDo any observers say that the person standing near the bus stop in the second slide was not moving? ExplainBased on these answers, explain what it means when someone says an object is “moving.”
7Observing MotionMotion requires an object moving over a distance or how far it has moved.When an object moves displacement takes place.
8Distance vs Displacement What is the difference between distance and displacement?Which should you use when calculating how many gallons of gas you will need for a road trip?Which does the saying “as the crow flies” refer to?
9Speed Speed tells you how fast something traveled over specific time. Speed is calculated as distance d divided by time t.s=d/tSpeed can also be measure in small spurts called instantaneous speed.Ex. Speedometer in a car
10Problem SituationI have dinner reservations at 8 pm at the Spaghetti Warehouse in Marietta off of exit I just got on I-75 South from Barrett Parkway at exit Assuming the distance from here to there is 10 miles, and it is now 7:50 pm, how fast must I drive to make my reservation?I know that Speed equals distance divided by timeDistance is 10 milesTime is 10 minutesSpeed = distance = miles = 1 mile / minute!time minutes
11Total Distance Covered Helpful HintAverage Speed = total distance coveredtravel timeTotal Distance CoveredDSTAverage SpeedTotal Time
12VelocityVelocity not only tells you the speed of an object but it also tells the direction.When velocity is calculated you use the same equation as speed, but you must specify direction.
13ProblemIt takes you 60 mins to travel 2km, what is your average speed?
14Graphing Motion A graph can be used to study motion Distance – Time graphx-axis= timey-axis= distanceThe slope of the line is the speed
15PracticeMake a line graph of the data of a runner. Determine the during which time interval the runner is moving faster, moving slower, and standing still. Explain the relationship between the slope of the line and the runner’s speed.Time (s)Position (m)102030
19Question?Which line shows the object covering the most ground in a certain amount of time?Position versus TimePositionEnd of Lecture was hereTime
20Some Names??We call the distance an object travels in a certain amount of time “speed”Speed = Distance coveredTimeTwo Types ofInstantaneousAverage
21Distance over Time is ? Distance versus Time 7 Distance (meters) 5 1 2 Time - (seconds)123Distance versus Time57Distance divided by time on this kind of graph is the:___________ of the object___________ of the line
22Question?Which line shows the object covering the most ground in a certain amount of time?Position versus TimePositionTime
23Question?Which object has the highest rate of speed or rather, which object is moving the fastest?Position versus TimePositionTime
24Question? Rank the five colors in order from slowest to fastest. Position versus TimePositionTime
25Changes Velocity is Speed + Direction How can we change our speed? How can we change our velocity?
26Acceleration Whenever your speed or direction changes you accelerate. Calculate accelerationa= vf-vi/t
27Think about itThink about your daily life. List 5 examples of acceleration. Classify each example of acceleration as an increase in speed, a decrease in speed, a change in direction, or a combination.
28Is your friend right?Your friend Lynn is getting frustrated that y’all are driving in circles [literally] trying to find the store. Lynn looks at the speedometer, sees its not moving from 25 mph and says: “Well, at least we are not accelerating while driving around the around the mall.” What do you say to Lynn?
29Revisit Motion Diagrams Spacing between dots represent what?Arrows represent what two things?If the object started to move faster towards the left, what would the diagram look like now?
30Check your representation skills! Construct a motion diagram for the ball in this video!Video
31Discuss with neighborWhich diagram below resembles your diagram the most?CDAB
32Discuss with neighborIn what direction is your CHANGE in velocity for that video/motion diagram?CABChange in velocity is zero
33Discuss with neighborIn what direction is your CHANGE in velocity for that video/motion diagram?CABChange in velocity is zero
35Create a storyDevise a story for an object whose motion is consistent with the motion diagram.DvDv = 0Dv
36Create a storyDvDevise a story for an object whose motion is consistent with the motion diagram to the right.DvDv = 0
37Throw the ball up now?We just did a motion diagram for a ball on its way down.Imagine, if I throw the ball up in the air? What does a motion diagram look like for the ball while it is moving upwards?While its at the top?
38Example ProblemI am standing on a cliff and I drop a rock from rest. After two seconds, the rock is moving at a speed of 20 m/s. What is the rate of acceleration for this rock?I know that acceleration equals change in velocity per unit timeChange in Velocity is 20 m/sTime is 2 secondsAcceleration = D velocity = m/s = m/s/s ortime s 10 m/s2
39QuestionIf I can accelerate at a rate of 15 mph per second, how long will it take me to accelerate from 30 to 90 miles per hour?
40QuestionIf I can accelerate at a rate of 15 mph per second, how long will it take me to accelerate from 30 to 90 miles per hour?2 seconds4 seconds8 seconds900 seconds
41QuestionYou are in your car going 75 mph. If you can decelerate your car at a rate of 25 mph per second, then how long does it take you to stop your car?
42QuestionYou are in your car going 75 mph. If you can decelerate your car at a rate of 25 mph per second, then how long does it take you to stop your car?100 seconds1/3 second3 seconds50 secondsWhat is the direction of the objects acceleration compared to the velocity of the car?
44ProblemA flowerpot falls off a second-story windowsill. The flowerpot starts from rest and hits the sidewalk 1.5s later with a velocity of 14.7m/s. Find the average acceleration of the flowerpot.
452-step acceleration/time/velocity You ride your bike at 2 m/s and accelerate at 0.2 m/s2 for 2 sec. What is your final velocity?
46Free Fall velocity?You jump from the second story building and hit the ground 2 seconds later. How fast were you falling when you hit the ground?
47Mathematical Representations learned thus far v = Dd / Dt = velocity equals change in displacement over change in timea = Dv / Dt = acceleration equals change in velocity over change in timeFree Fall Only Starting at Rest!!!!!!!a = g = 10 m/s2 [actually 9.8 m/s2]v = g t = velocity is g multiplied by timed = ½ g t2 = distance is one half multiplied by g multiplied by times squared.