the stopwatch method doesnt really work. firstly, it will give you average speed which isnt the same measurement method as you see on television for the pros. secondly, its HUGELY inaccurate!! even at an average speed of 50mph, the total measurement time is going to be 0.9 secs over 22 yards. the average human reaction time is 0.2 secs, and that applies to both the start and stop of the stopwatch. so potentially your measurement could be as low as 0.5 or as high as 1.3 secs. meaning your calculated speed could vary from 35-90mph!!
and that ignores the fact that the ball will most likely bounce, and thus lose quite a lot of speed. so its just not a good method at all.
the best method is to use a speed gun since thats how the pros are measured, and thus you have a more direct comparison. the second best method is to use a slow motion video camera, but thats more expensive than a speed gun, but some people might already own a camera that is capable of this.
its still not perfect since it has to average speed over the first few yards. but you can measure the delivery from side on with 2 known distance markers, then use freeze frame to calculate the speed from the video. it will be very close to the result of a speed gun.
0.00s - ball released
0.20s - human starts watch
0.90s - ball reaches wicket
1.10s - human stops watch
The time elapsed between the start and end of the ball's journey is the same as the time elapsed between the start and stop on the watch. There is no chance that will end up as 0.5 or 1.3 seconds. I am not denying there will be human error, but it cannot be to that extent.
Here's a few examples off Mitchell Johnson's current over.
Ball 1: timed at 0.47s (96mph) - Sky say 87mph
Ball 2: timed at 0.54s (83mph) - Sky say 86mph
Ball 3: timed at 0.43s (105mph) - Sky say 87mph
Ball 4: timed at 0.48s (94mph) - Sky say 89mph
Ball 5: timed at 0.61s (74mph) - Sky say 82mph [slower ball]
Ball 6: timed at 0.50s (90mph) - Sky say 87mph
My calculation of average speed: 90mph
Sky's calculation of average speed: 86mph
Over a period of time, and crucially with sensible averaging/discarding of outliers, you do get a pretty good idea. Obviously it would make a good deal of sense for me to ignore the measurement for ball 3 as 105mph is clearly crap, which then gives an average of 87mph... which ain't bad.
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its less likely that someone would hit the button before the event has happened, so in theory yes, you should be out by similar amounts on both pushes. but theres no guarantees there, and its hard to judge a ball hitting the pitch at 60+ mph from close range. watching cricket on TV you have the added benefit of seeing it from an elevated distance in high quality, at ground level youre going to need to be timing from roughly where the ball lands so that you can then also accurately measure the distance.
your average speed is fairly close. but that 3rd ball is still a long way off. 21% in fact. and as said, through ideal timing conditions watching from a distance on TV. executed well there is every possibility that real life timing COULD be within 2-3mph every time. but theres every chance it will be highly inaccurate. youre not going to know either way really, youve had the added benefit in your example of seeing the actual speeds on the TV to verify your measurements. in real life you dont have that (if you did then you wouldnt need the stopwatch lol). Johnsons actual speed spread was 7mph. yours is 31mph, which illustrates my point. even without the wayward measurement, its still 22mph. imagine thats a club bowler at 75mph and youre measuring anything from 65-85mph. thats a massive difference in speed from a batting perspective!
if you average the results over enough deliveries youd expect to be within 10%, so its better than nothing, and its free. but just take the results with caution. its not as accurate as a speed gun or slow motion camera. and this is assuming the person with the stopwatch is good at it. id imagine most people trying this would be kids, so you can easily see one of them going home telling their parents they bowled their mate out with a 100mph delivery at the nets!!
the other potential pitfall of the stopwatch method is whether you time the ball to the pitch, or time the ball past the stumps. its better to do it to the pitch, but then youve also got an estimated distance as a factor (a yard difference makes about 5% speed difference). if you time it past the stumps then you know the distance but youve got a bounce in there as well which is going to take speed off the ball and drop the average speed.
so like i said in the first place, it doesnt really work, compared to a speed gun. there are more accurate ways of doing it, but none of them are free unless you already own the equipment.
Last edited by Jim2109; 18-07-2010 at 04:18 AM.
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