Average Speed:Following Distance and Models of Motion
Learning Outcomes:
-Define and contrast average speed and instantaneous speed
-Use strobe photos, graphs, and an equation to describe speed
-Use a motion detector to measure speed
-Construct graphs of your motion
-Interpret distance time graphs
-Calculate speed, distance, and time using the equation for average speed.
"What do you see/ What do you think?"
Wednesday, September 21st
I see a car wreck, it looks like one car could not stop in time, so it almost caused a domino effect.
a.) a safe distance would not be what they are showing in the picture. someone obviously stopped short, and the people behind them were tailgaiting them... makeing it so they didnt have a big enough gap to have a fast enough reaction time.
b.) i think that the length between 2 cars should be 1-2 telephone poles.
Investigation:
Wednesday, September 21st
Strobe Photo: combined photo of pictures taken at equal intervals of time.
step 1: hook up motion detractor to USB port.
step 2: upload to USB drive.
step 3: open data studio.
step 4: screenshot graphs into wikis.
step 5: scrap paper, draw axes. (graph)
Walking towards slowly
Walking towards slowly
Walking away from slowly
Walking away from slowly
c.png
d.png
Homework Physics Talk Checking Up Q's
Sunday, September 25th
Physics Words: speed- the distance traveled per unit time; speed is a scalar quantity, it has no direction. constant speed- speed that does not change over a period of time. average speed- the total distance traveled divided by the time it took to travel that distance instantaneous speed- the speed at a given moment. velocity- the speed in a given direction. reaction distance -the distance a vehicle travels in the time it takes a driver to react.
Checking up questions: 1)Explain how the average speed of a vehicle is different from the instantaneous speed.
average speed is the total distance divided by the time , and instantaneous speed is the speed at a single point in time 2)How are the speed and velocity of an object different?
Speed is the distance traveled in a set time, but velocity deals with speed in a specific direction. 3)If the distance-time graph shows a straight, inclined line, what does the line represent?
It would be representing an increase in your distance per unit of time 4)How does reaction time affect reaction distance?
Reaction time affects reaction distance because depending on your reaction time will make a difference in your reaction distance, so if you have a slower reaction time you're going to have a greater reaction distance and the other way around.
Part 2 _- - - - -_ _
<----------------40mi---------------------->
3.)Suppose someone travels 50 mi at 50 mi/hr, travels 50 mi at 25 mi/hr, then travels 50 mi at 10 mi/hr
a.) Esmtimate their average speed.
b.) calculate the average speed. how close was it to your estimate.
Homework Physics to Go pages49-51 #1-11
Sunday, October 2nd
1.Describe the motion of each automobile below. The diagrams of strobe photos were taken every 3 s (seconds). a. The car is going at a constant speed (meaning that the speed is consistent and the same)
Screen_shot_2011-09-28_at_12.18.11_AM.png
b. The car is not going at a constant speed, because in the picture it looks like it is stopping short.
Screen_shot_2011-09-28_at_12.19.21_AM.png
2.Sketch diagrams of strobe photos of the following: a) An automobile starting from rest and reaching a final constant speed.
Photo_on_2011-09-28_at_00.21_#2.jpg
b) An automobile traveling at a constant speed then coming to a stop.
Photo_on_2011-09-28_at_00.22.jpg
3. A race car driver travels at 350 ft/s (that’s almost 250 mi/h) for 20 s. How far has the driver traveled during this time? 350 = d/20 d = 7000 feet 4. A salesperson drives the 215 mi from New York City to Washington, DC, in 4.5 h. a) What was her average speed? v = 215/4.5 v = 47.78 mi/h b) Do you know how fast she was going when she passed through Baltimore?Explain your answer. No because there is only enough information to calculate the average speed, not the instantaneous speed at a random point. 5. If you planned to bike to a park that was five miles away, what average speed would you have to maintain to arrive in about 15 min? (Hint: To compute your speed in miles per hour, consider this: What fraction of an hour is 15 min?) v = 5/.25 v = 20 mi/hr 6a. The automobile was traveling at a constant speed but then stopped. b. The automobile was traveling at a constant speed, stopped, then traveled backwards at a constant but slower speed. c. The automobile traveled at a slow but constant speed, the sped up but continued going at a constant speed. d. The automobile speed is increasing as time increases, but it is not constant. 7a. How far does your automobile travel in meters during your reaction time if you are moving at 55 mi/h (25 m/s)? 25 = d/.304 d = 7.6 m b. How far does your automobile travel during your reaction time if you are moving at 35 mi/h (16 m/s)? How does the distance compare with the distance at 55 mi/h? 16 = d/.304 d = 4.864 m The distance is shorter. c.Suppose you are very tired and your reaction time is doubled. How far would you travel at 55 mi/h during your reaction. 25 = d/.608 d = 15.2 m 8a. Experts would have had to find the average reaction time to be sure that 3 seconds is a safe following distance. b. A 3 second following distance will not be equally safe on the highway because you are traveling at a much faster speed, so you would need a farther following distance. 9. A sneeze requires you to close your eyes for one third of a second. a.If you are driving at 70 mi/h (100 ft/s), how far will you travel with your eyes closed during a sneeze? 100 = d/(1/3) d = 33.33 ft b.Is this longer than the length of your classroom? Yes, 33.33 ft is longer than the length of our classroom. 10.Imagine you are driving your automobile at 60 mi/h (88 ft/s) moving in a straight line and your reaction time is .5 s. a. How far does your automobile travel in this time? 88 = d/.5 d = 44 ft b. How many automobile spaces is this for an automobile that is 15 ft long? -About 3 automobile spaces. c. AnswerQuestions a) and b)when you travel 30 mi/h. (44 ft/s) 44 = d/.5 d = 22 ft About 1.5 automobile spaces. d. Answer Questions a) and b) when you travel 90 mi/h. (132 ft/s) What fraction of a football field is this distance? 132 = d/.5 d = 66 ft About 4.5 automobile spaces. e. If talking on the cell phone while driving at this speed doubles your reaction time, how do these distance numbers change at 30 mi/h, 60 mi/h, and 90 mi/h? All of the distances double. 11. Consider an automobile traveling at 60 mi/h. (88 ft/s). Sketch a graph showing distance traveled versus reaction time, with reaction times of .25 s, .5 s, .75 s, and 1 s. 88 = d/.25 d = 22 ft 88 = d/.5 d = 44 ft 88 = d/.75 d = 66 ft 88 = d/1 d = 88 ft
Distance vs Time Graphs Cyclists Monday, October 3rd
Photo_on_2011-10-03_at_08.27.jpg
a. Do the cyclists start at the same point? How do you know? If not, which is ahead? No. A started later than B. I know this because B already has distance.
b. At t=7s, which cyclist is ahead? How do you know? A is ahead, because A has a greater distance traveled.
c. Which cyclist is traveling faster at 3s? How do you know? B, because B has a greater distance.
d. Are their velocities equal at any time? How do you know? Yes their velocities are equal at 5s, because on the graph the lines intersect at that point.
e. What is happening at the intersection of lines A and B? Both A and B have traveled the same distance.
Photo_on_2011-10-03_at_08.28.jpg
4. Consider the position vs. time graph below for cyclists A and B.
a. How does the motion of the cyclist A in this graph compare to that of A in question 3? A Starts at 0 in both graphs.
b. How does the motion of cyclist B in this graph compare to that of B in question 3? B intersects a at 5s.
c. Which cyclist has the greater speed? How do you Know? A has a greater slope & speed. on the graph their speed is constantly increasing.
d. Describe what is happening at the intersection of A and B. The same distance is being traveled.
e. Which cyclist has traveled further during the first 5 seconds? How do you know? B, because B is above A on the graph up until 5s.
"Walking The Graphs": Tuesday, October 4th
#1.png
1.) Though it is not exact, the way we got the graph to look like this is the person starts by standing near the motion detector and instantaneously speeds up.
#2.png
2.)To get the graph to look like this took two people, one person stood far away from there while the other person quickly kicked their leg in front of the motion detector.
#3.png
3.) This graph was supposed to come out as a circle, as you can see this is impossible, you cannot even make the graph look like a circle because no matter what the time keeps moving. you would literally have to go back in time.
#4.png
4.) For this graph my group and I started further away from the motion detector, we had one person stand there and jump forwards then backwards fast.
#5.png
5.) For this one we did the opposite of the one above. we started close and jump backwards and then forwards really quickly.
Average Speed:Following Distance and Models of Motion
Learning Outcomes:
-Define and contrast average speed and instantaneous speed
-Use strobe photos, graphs, and an equation to describe speed
-Use a motion detector to measure speed
-Construct graphs of your motion
-Interpret distance time graphs
-Calculate speed, distance, and time using the equation for average speed.
"What do you see/ What do you think?"
Wednesday, September 21st
I see a car wreck, it looks like one car could not stop in time, so it almost caused a domino effect.
a.) a safe distance would not be what they are showing in the picture. someone obviously stopped short, and the people behind them were tailgaiting them... makeing it so they didnt have a big enough gap to have a fast enough reaction time.
b.) i think that the length between 2 cars should be 1-2 telephone poles.
Investigation:
Wednesday, September 21st
Strobe Photo: combined photo of pictures taken at equal intervals of time.
step 1: hook up motion detractor to USB port.
step 2: upload to USB drive.
step 3: open data studio.
step 4: screenshot graphs into wikis.
step 5: scrap paper, draw axes. (graph)
Homework Physics Talk Checking Up Q's
Sunday, September 25th
Physics Words:
speed- the distance traveled per unit time; speed is a scalar quantity, it has no direction.
constant speed- speed that does not change over a period of time.
average speed- the total distance traveled divided by the time it took to travel that distance
instantaneous speed- the speed at a given moment.
velocity- the speed in a given direction.
reaction distance -the distance a vehicle travels in the time it takes a driver to react.
Checking up questions:
1)Explain how the average speed of a vehicle is different from the instantaneous speed.
average speed is the total distance divided by the time , and instantaneous speed is the speed at a single point in time
2)How are the speed and velocity of an object different?
Speed is the distance traveled in a set time, but velocity deals with speed in a specific direction.
3)If the distance-time graph shows a straight, inclined line, what does the line represent?
It would be representing an increase in your distance per unit of time
4)How does reaction time affect reaction distance?
Reaction time affects reaction distance because depending on your reaction time will make a difference in your reaction distance, so if you have a slower reaction time you're going to have a greater reaction distance and the other way around.
DoNow:
Tuesday, September 27th
1). v=d/t, 90ft/s=d/ .6s, 54ft
2). 90= d/1.5s, 135ft
Video
d= 200m
t= 1:27-1:11= 16 sec
Vav= 200m/16s= 12.5m/s= 25 mph
Active Physics Plus p. 47
Wednesday, September 28th
Vav=?
Vav=80mi/∆t
Part 1: Vav= ∆d/∆t
20mi/hr=40mi/∆t1
∆t2=1 hour
Paragraph:
-Make a table of the trip
-FInd Vav
-Explain why Vav is closer to 1mph than 50mi/hr.
1.)
2.)Part 1: _- - _ _ _ _ _ _
<-----------------40mi------------------->
20 mi/hr
Part 2 _- - - - -_ _
<----------------40mi---------------------->
3.)Suppose someone travels 50 mi at 50 mi/hr, travels 50 mi at 25 mi/hr, then travels 50 mi at 10 mi/hr
a.) Esmtimate their average speed.
b.) calculate the average speed. how close was it to your estimate.
Homework Physics to Go pages 49-51 #1-11
Sunday, October 2nd
1.Describe the motion of each automobile below. The diagrams of strobe photos were taken every 3 s (seconds).
a. The car is going at a constant speed (meaning that the speed is consistent and the same)
b. The car is not going at a constant speed, because in the picture it looks like it is stopping short.
2.Sketch diagrams of strobe photos of the following:
a) An automobile starting from rest and reaching a final constant speed.
b) An automobile traveling at a constant speed then coming to a stop.
3. A race car driver travels at 350 ft/s (that’s almost 250 mi/h) for 20 s. How far has the driver traveled during this time?
350 = d/20
d = 7000 feet
4. A salesperson drives the 215 mi from New York City to Washington, DC, in 4.5 h.
a) What was her average speed?
v = 215/4.5
v = 47.78 mi/h
b) Do you know how fast she was going when she passed through Baltimore? Explain your answer.
No because there is only enough information to calculate the average speed, not the instantaneous speed at a random point.
5. If you planned to bike to a park that was five miles away, what average speed would you have to maintain to arrive in about 15 min? (Hint: To compute your speed in miles per hour, consider this: What fraction of an hour is 15 min?)
v = 5/.25
v = 20 mi/hr
6a. The automobile was traveling at a constant speed but then stopped.
b. The automobile was traveling at a constant speed, stopped, then traveled backwards at a constant but slower speed.
c. The automobile traveled at a slow but constant speed, the sped up but continued going at a constant speed.
d. The automobile speed is increasing as time increases, but it is not constant.
7a. How far does your automobile travel in meters during your reaction time if you are moving at 55 mi/h (25 m/s)?
25 = d/.304
d = 7.6 m
b. How far does your automobile travel during your reaction time if you are moving at 35 mi/h (16 m/s)? How does the distance compare with the distance at 55 mi/h?
16 = d/.304
d = 4.864 m The distance is shorter.
c. Suppose you are very tired and your reaction time is doubled. How far would you travel at 55 mi/h during your reaction.
25 = d/.608
d = 15.2 m
8a. Experts would have had to find the average reaction time to be sure that 3 seconds is a safe following distance.
b. A 3 second following distance will not be equally safe on the highway because you are traveling at a much faster speed, so you would need a farther following distance.
9. A sneeze requires you to close your eyes for one third of a second.
a. If you are driving at 70 mi/h (100 ft/s), how far will you travel with your eyes closed during a sneeze?
100 = d/(1/3)
d = 33.33 ft
b. Is this longer than the length of your classroom?
Yes, 33.33 ft is longer than the length of our classroom.
10. Imagine you are driving your automobile at 60 mi/h (88 ft/s) moving in a straight line and your reaction time is .5 s.
a. How far does your automobile travel in this time?
88 = d/.5
d = 44 ft
b. How many automobile spaces is this for an automobile that is 15 ft long?
-About 3 automobile spaces.
c. Answer Questions a) and b) when you travel 30 mi/h. (44 ft/s)
44 = d/.5
d = 22 ft About 1.5 automobile spaces.
d. Answer Questions a) and b) when you travel 90 mi/h. (132 ft/s) What fraction of a football field is this distance?
132 = d/.5
d = 66 ft About 4.5 automobile spaces.
e. If talking on the cell phone while driving at this speed doubles your reaction time, how do these distance numbers change at 30 mi/h, 60 mi/h, and 90 mi/h?
All of the distances double.
11. Consider an automobile traveling at 60 mi/h. (88 ft/s). Sketch a graph showing distance traveled versus reaction time, with reaction times of .25 s, .5 s, .75 s, and 1 s.
88 = d/.25
d = 22 ft
88 = d/.5
d = 44 ft
88 = d/.75
d = 66 ft
88 = d/1
d = 88 ft
Distance vs Time Graphs Cyclists
Monday, October 3rd
a. Do the cyclists start at the same point? How do you know? If not, which is ahead?
No. A started later than B. I know this because B already has distance.
b. At t=7s, which cyclist is ahead? How do you know?
A is ahead, because A has a greater distance traveled.
c. Which cyclist is traveling faster at 3s? How do you know?
B, because B has a greater distance.
d. Are their velocities equal at any time? How do you know?
Yes their velocities are equal at 5s, because on the graph the lines intersect at that point.
e. What is happening at the intersection of lines A and B?
Both A and B have traveled the same distance.
4. Consider the position vs. time graph below for cyclists A and B.
a. How does the motion of the cyclist A in this graph compare to that of A in question 3?
A Starts at 0 in both graphs.
b. How does the motion of cyclist B in this graph compare to that of B in question 3?
B intersects a at 5s.
c. Which cyclist has the greater speed? How do you Know?
A has a greater slope & speed. on the graph their speed is constantly increasing.
d. Describe what is happening at the intersection of A and B.
The same distance is being traveled.
e. Which cyclist has traveled further during the first 5 seconds? How do you know?
B, because B is above A on the graph up until 5s.
"Walking The Graphs":
Tuesday, October 4th
1.) Though it is not exact, the way we got the graph to look like this is the person starts by standing near the motion detector and instantaneously speeds up.
2.)To get the graph to look like this took two people, one person stood far away from there while the other person quickly kicked their leg in front of the motion detector.
3.) This graph was supposed to come out as a circle, as you can see this is impossible, you cannot even make the graph look like a circle because no matter what the time keeps moving. you would literally have to go back in time.
4.) For this graph my group and I started further away from the motion detector, we had one person stand there and jump forwards then backwards fast.
5.) For this one we did the opposite of the one above. we started close and jump backwards and then forwards really quickly.