newer measurement made on the path of travel suggests 140 +- 30 km/h
thanks to D wong for stimulating discussions.



Step1: use any YouTube down-loader such as thishttp://downloadyoutubevideo.org/download.php?url=http%3A%2F%2Fwww.youtube.com%2Fwatch%3Fv%3DS80bDrxrCiI%26feature%3Drelated



Step 2: save the video into the computer



Step 3: use tracker http://www.cabrillo.edu/~dbrown/tracker/ to open the video file






new estimates of length of car travel in video is now
13.0 1 m , still the cab bumper can be fitted by 1.81 m length






reason for readjusting the length of car traveled, results from a discussion with physics education expert D, Wong who suggested using nokia maps


http://maps.nokia.com/1.3005219,103.8561455,20,0,0,hybrid.day


to estimate the length of car in the video ( we measure from 2 white line of the
pedestrian walking to the center of the junction box. )






to estimate the length of car in the video ( we measure from 2 white line of the  pedestrian walking to the center of the junction box. ) show about 13 1 m, against the map scale on the bottom right 10 m





using tracker, the measurement of length is done easily using calibration tape (length to be measured)  and stick (10m)



















distance traveled by car is roughly 10 m and bumper of taxi is roughly 1.8 m (see diagram)





Step 4 :state assumptions made:


  1. taxi camera is stationary for the duration of the 0.3 seconds the Ferrari sped across

  2. the height of the traffic light post is approximately 2.0 m from base to green light center

  3. distance traveled by car is roughly
    13 1  10 m and bumper of taxi is roughly 1.8 m (see diagram)

  4. the video is properly time-frame as 30 frame/seconds as default in the video data, and read correctly by tracker.

  5. the Ferrari is traveling at constant acceleration = 0 m/s^2track the front of the Ferrari.


Step 5: calibrate pixels in video with known lengths, improved strategy after discussion on Facebook distance traveled by car is roughly
13 1  10 m and bumper of taxi is roughly 1.8 m.



Step 6: Make roughly 8 to 9 points as shown








Make roughly 8 to 9 points as shown










using tracker to trace the motion of the car



Step 7: .Analyze the speed









7.1 s vs t graph, which is roughly 39.23 m/s from as evidence from the






linear fit x = 39.231*t + -0.352 where a = 39.231 which means the average velocity assuming a constant velocity motion








linear fit x = 30.187*t + -0.271 where a = 30.187 which means the average velocity assuming a constant velocity motion






linear fit x = 60.178*t + -13.821 where a = 60.178 which means the average velocity assuming a constant velocity motion







linear fit x = 60.178*t + -13.821by comparing coefficient to constant acceleration equation x = u*t + x0roughly u = 60 m/s





7.2 v vs t graph statistic mean v average = 39.75     30(wrong estimate)  60 (wrong estimate) m/s








data tool notice the mean for x is 3.975E1 which means 39.75, another evidence of average velocity








data tool notice the mean for x is 3.059E1 which means 30.059, another evidence of average velocity






data tool notice the mean for x is 6.097E1 which means 60.97, another evidence of average velocity





average it out = (39.231+39.75)/2 = 39.5 m/s



Error Analysis:

assume average v = d/t

error analysis suggests,




?v/v = ?d/d + ?t/t




using estimates of




?d = 1 m (estimate from nokia map), d = 13 (nokia map)




?t = 1/30 (from framerate) , t = 0.30 (from tracker)




v = 140 m




therefore, ?v = 0.18*v = 26
? 30 m/s (1 sign figure)



Conclusion:




when converted to km/hr, v = 39.5*3600/1000 = 142 km/hr ? 140 30 km/hr ( follow the order of magnitude of the error)










Claim:

The vehicle is likely to be traveling at speed of 140 30 (current best estimate, as of 17May2012)





Question:

What do you think ??



Source of errors:


  1. moving source camera and some parallax error taxi camera was not stationary for the duration of the 0.3 seconds the Ferrari sped across.

  2. the distance traveled by the car may not be corrected measure, thus, a nokia map was used to check.

  3. the height of the traffic light post is not 2.0 m from base to green light center

  4. the source of the video could not be verified in the time frame used to capture the video, and the time-frame may not be  30 frame/seconds, though it is likely to be correct.




Physics & Science lesson learn could be:






Morale lessons caught could be:  




Open Content Sharing of Educational resources creative commons attribution:

the video, trk files are downloadable at NTNU java Forum http://www.phy.ntnu.edu.tw/ntnujava/index.php?topic=2447.0 , available to registered users of the forum, registration is FREE.

* trackerF04.png (324.91 KB, 1280x994  )

* videoplaybackwee.trk (14.38 KB  )

* videoplaybackwee.zip (2382.25 KB ) based on incorrect light post height

* videoplaybackwee01.zip (2594.63 KB ) based on incorrect length of car traveled in video evidences and measurements

* videoplaybackwee02.zip (2996.85 KB) based on better estimates of length of car travel




Disclaimer:

This post is made with the best intentions to share good active learning practices in physics education, any offenses taken please leave a comment, i will amend the post or/and to remove offensive content if any.



The mass media media corp 5 news also reported on the accident.