Physics and the racing start.

Look at the start in lane 4 http://youtu.be/AFelAOGlN4M Thanks eaglesrest

Interesting thread. To me it seems pretty clear that the differences in technique reflect the track start and the wedge in the rear, and so reflect a trade-off between reaction time and distance. With the regular blocks (no wedge) it isn't clear to me the trade-off is worthwhile. From what I remember -- and my memory is always suspect nowadays -- most people do not use a version of the track start on relay exchanges, where reaction time is not an issue. A lot of people nowadays seem to use some version of the "step-up" start where you combine some momentum and the greater power of pushing off with two feet. If the track start were indeed the most powerful kind of start, wouldn't we see it almost exclusively on relays too?

Unless there is a mechanical advantage to one start over the other,the initial velocity will be identical. The horizontal vector of the flat start will be greater than of the angled up start.The vertical vector of the angled start will decrease,reach zero and then increase to faster than the flat start's(falling from 4 1/2 feet you reach a faster velocity than from 3.) I would agree that if the initial velocities are identical that projectile motion equations take over and the higher angled start would be the most efficient. Since you are at a height above the water's surface, the optimal angle actually depends upon your initial velocity. As velocity gets higher, the optimal angle approaches 45 degrees. Human limitations on leaping ability would keep this optimal angle between 25 and 35 degrees. However, there is an initial phase of the start where you accelerate your mass from zero to your initial velocity (the moment when your body no longer applies any force against the block). Modeling this phase would be horribly complicated because we don't really apply a constant force evenly over the entire phase in a straight line. But for argument sake, I *think* it would be most like a frictionless inclined plane (see here for diagrams under Frictionless Inclined Planes with Pulleys). The pulleys aren't necessary but they kind of illustrate the forces acting upon our bodies during the start. There is a force acting in the direction of the inclined plane represented by "T" and a gravitational force acting against that which gets larger depending upon how big the incline is. So, from Newton's second law, T - m*g*sin(x) = m*a where T = to our leaping force, m=our mass, g=gravity and x=the angle of the jump. Assuming that I can jump at twice the force of gravity (I have no idea how much force I actually produce when I jump), this becomes: 2*m*g - m*g*sin(x) = m*a or... a = g*(2 - sin(x)) For a 30 degree angle, this comes out to 14.7 m/s^2 For a 0 degree angle, this comes out to 19.6 m/s^2 Velocity = a*t so for any given time increment, the velocity should be about 30% higher for a flat start. That doesn't mean that you won't hit the water faster with an inclined jump or that you will hit the water at a shorter distance from the wall. I just don't think you can assume that the initial velocity is the same no matter what angle you jump from. I'd be OK with assuming the jumping force is the same (I have reasons to doubt this also... especially with track starts) but not the velocity at which you leave the blocks. Of course, my inclined plane model might have plenty of holes in it and all of this is baseless. I'm certainly willing to be corrected if there is a better way to look at it.

I have yet to hear an argument based on science for not maximizing distance in the air. Think of it this way. You've got a finite amount of power that your legs can supply. Would you rather use that power to propel you forward or upward? I agree that you'll go faster through the air, but there's definitely a tradeoff. As quicksilver mentioned, hang time isn't helping in swimming.

Think of it this way. You've got a finite amount of power that your legs can supply. Would you rather use that power to propel you forward or upward? I agree that you'll go faster through the air, but there's definitely a tradeoff. As quicksilver mentioned, hang time isn't helping in swimming. Hang time doesn't help in swimming if it doesn't get you out further.If it does,then I submit that it does help.Even if you are diving straight out,if you have better leg power you are going to go further and that is going to be faster,otherwise people would dive down off the blocks at a steeper angle.Back in my younger days I had a really good vertical jump(30") and it was a common occurrence for me to see my competition enter the water while I was still in the air.In those cases I was coming up 1/2 body length ahead on the breakout.

I found this site some years ago quickgetaway.com/ps01-intro.htm .There discussion makes sense to me. I'm not sure why their ideas didn't catch on,maybe somebody out there knows the history. I'm afraid this thread has become a bit of someone saying the the straight out start is good because of X and my saying,no you are wrong because Y.That is really not my intent,I am looking for the physics to back up any claim. I hope I am prepared to agree with a compelling argument in favor of the straight out start.

I would agree that if the initial velocities are identical that projectile motion equations take over and the higher angled start would be the most efficient. Since you are at a height above the water's surface, the optimal angle actually depends upon your initial velocity. As velocity gets higher, the optimal angle approaches 45 degrees. Human limitations on leaping ability would keep this optimal angle between 25 and 35 degrees. However, there is an initial phase of the start where you accelerate your mass from zero to your initial velocity (the moment when your body no longer applies any force against the block). Modeling this phase would be horribly complicated because we don't really apply a constant force evenly over the entire phase in a straight line. But for argument sake, I *think* it would be most like a frictionless inclined plane (see here for diagrams under Frictionless Inclined Planes with Pulleys). The pulleys aren't necessary but they kind of illustrate the forces acting upon our bodies during the start. There is a force acting in the direction of the inclined plane represented by "T" and a gravitational force acting against that which gets larger depending upon how big the incline is. So, from Newton's second law, T - m*g*sin(x) = m*a where T = to our leaping force, m=our mass, g=gravity and x=the angle of the jump. Assuming that I can jump at twice the force of gravity (I have no idea how much force I actually produce when I jump), this becomes: 2*m*g - m*g*sin(x) = m*a or... a = g*(2 - sin(x)) For a 30 degree angle, this comes out to 14.7 m/s^2 For a 0 degree angle, this comes out to 19.6 m/s^2 Velocity = a*t so for any given time increment, the velocity should be about 30% higher for a flat start. That doesn't mean that you won't hit the water faster with an inclined jump or that you will hit the water at a shorter distance from the wall. I just don't think you can assume that the initial velocity is the same no matter what angle you jump from. I'd be OK with assuming the jumping force is the same (I have reasons to doubt this also... especially with track starts) but not the velocity at which you leave the blocks. Of course, my inclined plane model might have plenty of holes in it and all of this is baseless. I'm certainly willing to be corrected if there is a better way to look at it. Wow... Have a :chug: for all of that...

Isn't this banned in many states now? ...meaning blocks have to be positioned in the deep end. 4ft. is the minimum depth for diving from blocks, and I'll be diving into a meet this next weekend that is 4ft. 3in. :) Still, keep it shallow. :afraid: 107.2.3 Water Depth A Starting end—Minimum water depth for racing starts, as measured for a distance of 3 feet, 3½ inches (1.0 meter) to 16 feet, 5 inches (5.0 meters) from the end wall, during either competition or practice shall be as follows: (1) In pools with water depth less than 3 feet, 6 inches (1.07 meters) at the starting end, the swimmer must start within the water. (2) In pools with water depth 3 feet, 6 inches (1.07 meters) to less than 4 feet (1.22 meters) at the starting end, the swimmer must start from the deck or from within the water. (3) In pools with water depth 4 feet (1.22 meters) or more at the starting end, platforms shall meet the height requirements of article 107.11.1.

While you made some assumptions that may or may not be accurate,the overall gestalt helps me.I'm far better at wild assumptions than I am at physics :).

...who can still beat most sprinters off the blocks. :banana: ...because out of respect they dare not enter the water before you do. :) Stay thirsty my friends. A 4 foot depth at some pools must be approached much differently than a 9 foot depth at most of the "good" pools. Isn't this banned in many states now? ...meaning blocks have to be positioned in the deep end.