newer measurement made on the path of travel suggests 140 + 30 km/h
thanks to D wong for stimulating discussions.
Step1: use any YouTube downloader such as this
http://downloadyoutubevideo.org/download.php?url=http%3A%2F%2Fwww.youtube.com%2Fwatch%3Fv%3DS80bDrxrCiI%26feature%3DrelatedStep 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
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:
 taxi camera is stationary for the duration of the 0.3 seconds the Ferrari sped across
the height of the traffic light post is approximately 2.0 m from base to green light center
 distance traveled by car is roughly
13 ± 1 10 m and bumper of taxi is roughly 1.8 m (see diagram)
 the video is properly timeframe as 30 frame/seconds as default in the video data, and read correctly by tracker.
 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/s7.2 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/terror analysis suggests,
Δv/v = Δd/d + Δt/t
using estimates of
Δd = 1 m (estimate from nokia map), d = 13 (nokia map)
Δt = 1/30 (from framerate) , t = 0.30 (from tracker)
v = 140 m
therefore, Δv = 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:
 moving source camera and some parallax error taxi camera was not stationary for the duration of the 0.3 seconds the Ferrari sped across.
 the distance traveled by the car may not be corrected measure, thus, a nokia map was used to check.
the height of the traffic light post is not 2.0 m from base to green light center
 the source of the video could not be verified in the time frame used to capture the video, and the timeframe may not be 30 frame/seconds, though it is likely to be correct.
Physics & Science lesson learn could be:
 Using current affairs to educate the children on everyday physics and making physics relevant.
 using evidences to justify claims.
 science knowledge is socially constructed with newer evidences suggesting better ways of explaining the phenomena.
Morale lessons caught could be:
 Don't drive recklessly.
 Don't beat red lights.
 Be responsible
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.