Maybe a dumb question, but hey who cares?
I was at the BEST ever olympics recently, and I saw the 100 meter sprint. Now my question is how do they time each individual?
Before you jump in, think about this - if they used a laser or beam that gets broken on crossing the line then you will only definately get the first place time (the others could be within a body width behind). Any ideas??
Each lane on the track has its own sensor. I believe they consist of a small motion detector embedded in the track itself. Back in the day, of course, you just had a seperate stopwatch guy for each runner.
Fair enough - but I am a little dubious. Obviously it has to be an each lane thing, but will a motion detector cut it?
We are talking about 1/100 of a second, and it has to be chest height (I think that is the rule).
In discussion with friends we thought of lasers from above -but the head could break the beam. We thought of some sort of detector in the shoes - but each athlete would need it fitted and that is not chest height. A laser pointing down each lane maybe? But how does it know when the athlete crosses the line?
Still perplexed!
I think it’s the same equipment that is used for horse racing. The timer is hooked up to the starter’s pistol. Once it goes, off the clock is started.
There are sensors in the starting blocks and if the runner’s feet leave the blocks before the gun or more quickly than humanly possible (i.e., a rolling start), then it’s a false start.
Then everybody flies down the track. There is a sensor with a camera attached at the finish line. Once your body crosses the sensor (which I think is at chest level), a picture is snapped. Runner #2 then gets a picture and so on. The pictures have a time stamp on them. When the photo taken by the finish line camera is viewed, you can see how close the finish was.
I don’t think there are sensors in the lanes of the track. If a runner drifts out of his/her lane, that is usually noticed during the race or on appeal by watching a videotape.
The timers actually record the time to 1/1000th of a second, but only times to 1/100th are officially reported.
Bob, that all makes sense and matches what I had heard with the start and stuff, but if the finish is a a sensor, what happens when runner 1 crosses - very fast camera goes off - then runner 2 crosses but from a right angle to the track view there is no gap between 1 and 2. How does the sensor know when 2 crosses (also note that the sensor would not necessarily be on the side of the track closest to runner 2).
I guess what I am looking for is what type of sensor detects the crossing of a single line at multiple points that may overlap from a side angle? (whoah have I just cleared that up or what - not!)
“They” can do similar with radar speed detectors on multiple lanes but they are not that accurate.
PS: as a by-line did you know that the under water camera in the pool (you know the one that showed the Aussies winning the 4X100 relay 
) was moved along by a guy in a back room “peddalling” with his hand on winch - great technology huh?
You can go to http://www.swatch.com and pull up the photo finishes of all the races if you’d like.
It appears to me that the camera itself is mounted on the finish line but quite a few meters above the track. This allows everyone to show up in the photo.
The one I’m looking at is for Heat 11 of the Men’s 100. The 4th and 5th placer finished 0.02 seconds apart and it’s quite easy to tell the difference.
(I’d post a link right to it, except I’m not quite sure how to do it for this sort of link, which is a bit weird.)
I’ve poked around the site and Swatch doesn’t seem to exactly say how everything is done, but in the glossary it provides there is a mention of a contact strip on the track, but I don’t see that working because not every runner is going to step on that sensor when crossing the line.
I’m sure somebody else knows this answer for certain.
[hijack]
The reason times are only given to 1/100th of a second is not due to the accuracy of timing, but that you can’t build a 100m track to so tight a specification.
And this doesn’t even consider the scenario shown in the episode from the TV show “The Games” when the 100m track was actually only 94m due to the need to lay down the TV cables. 
[/hijack]