I watched the video on Schoeman's start swimswam.com/.../ and it raised a question I have had for a long time;why jump straight out from the start? Schoeman noted another swimmer who dove slightly up at the start and "stalled out"..In a previous thread Rich Abrahams said a coach told him the same thing about stalling out.The physics of this statement make no sense to me.Horizontal velocity is going to remain fairly constant,vertical velocity will decrease as one goes up and then increase again past the apex. I emailed Brent Rushall and he said to jump straight out or slightly down,but the article he referenced said
" Enter the water steeper rather than flatter (this should reduce the amount of splash (irrelevant water movement)).
Practice diving out as far as possible (maximal horizontal velocity produced primarily by leg drive off the block) before entering the water.
Dive deep so that resistance is reduced and more effective double-leg kicks are executed before surfacing."
To maximize distance(diving as far out as possible) one should angle up about 35-40 degrees(if the top of the block was even with surface of the water it would be 45 degrees(Rob Copeland said 32 degrees in another thread but: en.wikipedia.org/.../Ballistic_trajectory )
No one still does that,but some really good starters used to 1984 Olympic Men's 100m Breaststroke final - Steve Lundquist - YouTube .
When I ask coaches why the start should be straight out instead of angled up I never get an answer other than it has been found to be faster.In researching "found to be faster" I have found very little real confirmation.The best study I found(which I can no longer find the reference for) stated that the most important variable in speed to 15M was clean entry and that the greatest correlation with clean entry was experience.This also means that studies that just compare speed to 15M of different starts need to take experience with the start into account.
When I try the straight out start I have variable success with my entry(as would be expected with a new start.)I am willing to practice to get more consistent if I can get an explanation of why it is faster that makes "physics sense". I have seen too many trends in swimming change to think something is right just because everyone does it.(The first lesson I learned about starting was "ït is not a good start if it doesn't give you a red chest". I have been variously taught to swim freestyle without rolling and to kick out on BR kick so I know common wisdom isn't always wise.)
Why is there a starting distance in your calculations? Is it an approximation of how much the block moves under Fort's earthquake like 6.0 start?
My understanding from Peter's analysis - the swimmer is 2m long and so when the feet leave the block at end of force application, when swimmer then becomes projectile-like in a horizontal position, his CG is already 1m from the starting wall. If you look at his caclulation of the 30 deg start, you'll notice that swimmer's CG is only .87m from the wall because of the vertical takeoff (cos angle). Peter damn near thought of eveything!
Its interesting that James's and Fort's reaction times of around .6 sec are greater than the time from block to the water (calculated by Peter ~.4 to .6 sec). It would interesting to time Fort, or James or both from when feet leave the block to the point where they hit the water. Then time from the point where they hit the water to the 15m mark (pullout).
This would allow caclulation of the component horizontal velocities and we'd have actual velocities in the air and actual sdk velocities underwater 'til pull out. Peter is using 4.55m/s (= 25 m in 5.5 sec) in the air and assumed 25% less for underwater sdk or underwater Vx ~3.4m/s (= 25m in 7.35 sec). Possibly a little high for underwater, even for Fort and James? Having the three components: reaction time; air time and distance; and underwater time and distance; it would be easy to evaluate where the actual relative potential time savings are in a start.
Kicking speed vs swimming speed would (or should) strongly influence start strategy. I don't know how many max effort starts (to the 15M) you could string together and still have timing be meaningful.
Maybe measure times and calc velocities (as above) at a meet that has the capability to measure reaction times and where they are swimming 3 or 4 events with some rest between starts.
Why is there a starting distance in your calculations? Is it an approximation of how much the block moves under Fort's earthquake like 6.0 start?
My understanding from Peter's analysis - the swimmer is 2m long and so when the feet leave the block at end of force application, when swimmer then becomes projectile-like in a horizontal position, his CG is already 1m from the starting wall. If you look at his caclulation of the 30 deg start, you'll notice that swimmer's CG is only .87m from the wall because of the vertical takeoff (cos angle). Peter damn near thought of eveything!
Its interesting that James's and Fort's reaction times of around .6 sec are greater than the time from block to the water (calculated by Peter ~.4 to .6 sec). It would interesting to time Fort, or James or both from when feet leave the block to the point where they hit the water. Then time from the point where they hit the water to the 15m mark (pullout).
This would allow caclulation of the component horizontal velocities and we'd have actual velocities in the air and actual sdk velocities underwater 'til pull out. Peter is using 4.55m/s (= 25 m in 5.5 sec) in the air and assumed 25% less for underwater sdk or underwater Vx ~3.4m/s (= 25m in 7.35 sec). Possibly a little high for underwater, even for Fort and James? Having the three components: reaction time; air time and distance; and underwater time and distance; it would be easy to evaluate where the actual relative potential time savings are in a start.
Kicking speed vs swimming speed would (or should) strongly influence start strategy. I don't know how many max effort starts (to the 15M) you could string together and still have timing be meaningful.
Maybe measure times and calc velocities (as above) at a meet that has the capability to measure reaction times and where they are swimming 3 or 4 events with some rest between starts.
