You need to describe the motion of a motor vehicle while you are driving What factors affect ◦...
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UNDERSTANDING MOTION
Transcript of You need to describe the motion of a motor vehicle while you are driving What factors affect ◦...
UNDERSTANDING MOTION
You need to describe the motion of a motor vehicle while you are driving
What factors affect ◦ Following distance◦ Braking distance◦ The total stopping distance
CHAPTER CHALLENGE REMINDER
SPEED AFFECTS ALL OF THESE!!!
Speed – the distance traveled per unit time
Constant speed – speed that does not change over a period of time
WHAT IS SPEED?
Model 1: Strobe photos Model 2: Equations
◦ Average speed = (distance traveled)/(time elapsed)
◦ vav = Δd/Δt
DESCRIBING MOTION
Speed – the distance traveled per unit timeConstant speed – speed that does not change over a period of timeAverage speed – the total distance traveled divided by the time it took to travel that distance
WHAT IS SPEED?
vav
Δd
Δt
If you drive a distance of 400 mi (640 km) in 8 h, what is your average speed?
SAMPLE PROBLEMS
Speed – the distance traveled per unit timeConstant speed – speed that does not change over a period of timeAverage speed – the total distance traveled divided by the time it took to travel that distanceInstantaneous speed – the speed at a given moment
WHAT IS SPEED?
You are traveling at 35 mph (~50 ft/s) and your reaction time is 0.2 s. Calculate the distance you travel during your reaction time.
SAMPLE PROBLEMS
vav
ΔdΔt
In an automobile collision, it was determined that a car traveled 150 feet before the brakes were applied.◦ If the car had been traveling at the speed limit of
40 mph (60 ft/s), what was the driver’s reaction-time?
◦ Witnesses say that the driver appeared to be under the influence of alcohol. Does your reaction-time data support the witnesses’ testimony?
SAMPLE PROBLEMS
Speed – the distance traveled per unit timeConstant speed – speed that does not change over a period of timeAverage speed – the total distance traveled divided by the time it took to travel that distanceInstantaneous speed – the speed at a given momentVelocity – the speed in a given direction
WHAT IS SPEED?
Model 1: Strobe photos Model 2: Equations
◦ Average speed = (distance traveled)/(time elapsed)
◦ vav = Δd/Δt Model 3: Graphs
◦ Distance-Time Graph
DESCRIBING MOTION
Model 3: Graphs◦ Distance-Time GraphsGraph 1
Graph 2
Graph 3
Graph 4
DESCRIBING MOTION
Displacement – the difference in position between a final position and an initial position; it depends only on the endpoints, not the path; displacement is a vector quantity, it has magnitude (size) and direction
WHAT IS DISPLACEMENT
Model 3: Graphs◦ Distance-Time GraphsGraph 5
Graph 6
Graph 7
Graph 8
DESCRIBING MOTION
Reaction Distance – the distance that a vehicle travels in the time it takes the driver to react
How is this related to Reaction Time?
Coming Around Full Circle
What is a safe following distance between your automobile and the vehicle in front of you?◦ Speed: 55 mph (81 ft/s)◦ Avg Reaction Time: 0.15 s ◦ Avg Car Length: 13 ft
How do you decide what a safe following distance is?
What Do You Think Now?
Driving at 1 sec distance, 2 sec distance and 3 sec distance◦ http://youtu.be/PsAafpeOOZg
3 Second Rule
Claim: A distance-time graph will have a greater slope if an object is moving fasterEvidence: Does your data support or refute this claim?Instructions: Make 2 graphs (rise: 50m; run: 10s). One will reach 50m in 10s, and the other will reach 25m in 10s
Claim and Evidence
Study Guide: Questions 8-15, 17-19Tutoring Weekdays: 8:00AM Mondays and Wednesdays: 3:45PM
Homework
