Radar guns

[vroomfondel]

questions- 1. where do they put it? 2. when does it measure the ball? 3. how is it at all accurate if it can only measure velocity component in the direction of the gun? Is it placed at an upward angle? ie, if Ishant bowls a half-trekker (sic ramiz) from about 2.5m high, the trajectory of the ball means that there's a 5% error in measurement, so a ball at ~145 ends up at ~140 etc. do they account for this? same question apply to tennis too, i guess. kthx

[Sachinism]

The speed is usually measured as it leaves the hand and then it quickly dies down in pace

[Ram]

1. where do they put it?

My guess is its mounted right behind the bowler's arm, on both the ends, so that the ball is right in the range of the gun's radio waves.

2. when does it measure the ball?

There is no one particular moment. The speed of the ball is measured from the moment is leaves the bowler's hand.

3. how is it at all accurate if it can only measure velocity component in the direction of the gun? Is it placed at an upward angle? ie, if Ishant bowls a half-trekker (sic ramiz) from about 2.5m high, the trajectory of the ball means that there's a 5% error in measurement, so a ball at ~145 ends up at ~140 etc. do they account for this?

Most radar speed guns work on Doppler effect, which as you may already know, is the apparent change in frequency of a wave, due to relative motion between source and observer. So, where is the question measuring the velocity component in the direction of gun. Is it not what happens all the time? ( i.e, gun placed right behind and infront of the bowler's arm). My guess is, they take the readings from the guns at both the ends to check for accuracy. Btw, the '145 kmph' you see is the speed of the ball out of the bowler's hand. So, what the ball does after that ( short pitch, full pitch, yorker), is immaterial as far as the reading on the T.V is concerned.

[vroomfondel]

Doppler effect

doppler shift is caused only by component of velocity parallel to the direction of propagation of your RF. ie, if the ball was moving up the page, and the detector was placed to the right then you would measure 0 velocity. it's like just dropping a ball straight down, you would see no reading on the doppler. /\ | |<-----------------> [detector] | | /\ so it doesn't actually measure total velocity - just in the direction of the batsman...ie. fuller balls should show up as slightly faster than short pitched balls. I don't remember if this is true.

[cochise]

Yes, correct...fuller balls will have a higher component of velocity in the direction (or against the direction if the detector is placed in front of the bowler as opposed to behind) of propagation of the wave. Lateral and perpendicluar components will not enter into the reading...more advanced radar that emit and receive 3D wavefront cross-section can resolve all three components with some accuracy...like airplane radars etc...at least in principle, that is possible.

[observer1]

the forum's resident nuclear physicist/ buddhist philosopher has a phd thesis on speedguns.