Physics and the racing start.

RE: Physics and the racing start.

Allen Stark — Wed, 06 Feb 2013 02:22:20 GMT

I got a coach friend of mine to time my starts.There is a red line across the pool at about 35 feet so he timed to there.This is hand timed so although it is to .01s it is not that accurate. Regular grab start-4.95 My regular track start-5.00(basically the same,but since I am more practiced with the grab start I'd say probably faster with practice.) Grab start with angle up to maximize flight time-5.15(ouch) Grabbing the side of the block and leaning forward,which the coach thought would be fastest ,but he wouldn't recommend as too easy to get DQd-5.15 Then he coached me on the track start, narrowing my stance,putting my hands wider,angling my back foot more upright-4.75 Now I know what to work on.

RE: Physics and the racing start.

Former Member — Tue, 27 Nov 2012 15:45:39 GMT

the starting distance is 1 meter from the wall. 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? Don't be silly. It's very easy. You take the coefficient of the horizontal distance and multiple it by the amplitude of how much force is being applied at the moment of inertia. kg * m^2 / s^2? He simplified it as follows: I appreciate your concern that I might hurt myself trying to understand where pmccoy's numbers came from. Empirical is the way to go. Videotape and time lots of starts to the 15 meter mark. Vary things like takeoff angle and entry angle and see how these seem to affect time to distance. It would really be cool to be able to overlay multiple starts and see the differences. That would be cool. 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.

RE: Physics and the racing start.

pmccoy — Tue, 27 Nov 2012 12:53:10 GMT

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! All those free body diagrams in college and they finally pay off 20 years later! I'm contemplating a cheap way of setting things up for empirical analysis. I've got an underwater camera. I just need a way of marking distance for video in the pool. Might take a couple weeks but I'm curious enough to try this out.

RE: Physics and the racing start.

Sojerz — Tue, 27 Nov 2012 12:44:01 GMT

Actually I was thinking the same thing myself.I have a taper meet this weekend so it will need to wait til after that. I think I can be with Fort to 15Min BR(if SDK is involved she'll kill me.) Allen swimming Br too would provide another dimesnion. That would be three swimmers for this experiment.:banana:

RE: Physics and the racing start.

Sojerz — Tue, 27 Nov 2012 12:37:40 GMT

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.

RE: Physics and the racing start.

knelson — Tue, 27 Nov 2012 12:16:35 GMT

I'll see if there is an easy way to estimate this but I'd guess that and empirical approach would be much easier. Yeah, I don't think there is. There are just too many variables. If you start by assuming the human body is going to behave like a streamlined, rigid object you could certainly do it, but to me that's not a good assumption at all. We all know that exactly how your body enters the water on a dive is very important just from observation. Empirical is the way to go. Videotape and time lots of starts to the 15 meter mark. Vary things like takeoff angle and entry angle and see how these seem to affect time to distance. It would really be cool to be able to overlay multiple starts and see the differences.

RE: Physics and the racing start.

Allen Stark — Tue, 27 Nov 2012 12:13:00 GMT

Agreed. Allen needs to go try different start techniques at stop pestering us with mathematical justifications for one side or the other. When he gets to the 15M mark faster than Fort, he should stick with that approach. Actually I was thinking the same thing myself.I have a taper meet this weekend so it will need to wait til after that. I think I can be with Fort to 15Min BR(if SDK is involved she'll kill me.)

RE: Physics and the racing start.

rxleakem — Tue, 27 Nov 2012 10:07:46 GMT

My son just showed this to me. Perhaps it will help with this conversation? :dunno: 3706

RE: Physics and the racing start.

Former Member — Tue, 27 Nov 2012 09:44:46 GMT

I'm contemplating a cheap way of setting things up for empirical analysis. I've got an underwater camera. I just need a way of marking distance for video in the pool. Might take a couple weeks but I'm curious enough to try this out. High speed HD video camera, fixed position. The video editing software does all the work. If you are just comparing starts, you need to mark two points. The point that you set the camera on and the point that you aim the camera at and you can duplicate the setup so that you can compare starts across different days (assuming the same pool). Underwater analysis is much more difficult mainly because lighting has to be really good for a fixed camera point to be able to "see" well enough across 15m for analysis. I predict that your biggest bang will come from just practicing starts. If you compared two techniques with max effort, trained starts for a month, then compared them again, the starts at the beginning would not be nearly as fast as the starts at the end.

RE: Physics and the racing start.

Former Member — Tue, 27 Nov 2012 08:16:56 GMT

Actually I was thinking the same thing myself.I have a taper meet this weekend so it will need to wait til after that. I think I can be with Fort to 15Min BR(if SDK is involved she'll kill me.) Then you should use van der Burgh as your benchmark to be fair.

RE: Physics and the racing start.

Allen Stark — Tue, 27 Nov 2012 05:19:19 GMT

When I get the time(after the next meet) I was hoping to get time to entry,distance to entry and time to 15M for flat,slightly up,and about 30 degrees for grab and track starts.This won't be a totally fair comparison given my familiarity with my current(grab) start but it will give some(hopefully interesting) data. The other thing this may help me with is how much if any distance is lost from track start(without fin) compared to grab start. I'll post what I get when I get it.Please post the results of any experiments Yáll conduct.

RE: Physics and the racing start.

The Fortress — Tue, 27 Nov 2012 04:02:41 GMT

Then you should use van der Burgh as your benchmark to be fair. As a non-evilstroker, I should, to be fair. :)

RE: Physics and the racing start.

Sojerz — Tue, 27 Nov 2012 01:24:27 GMT

All those free body diagrams in college and they finally pay off 20 years later! I'm contemplating a cheap way of setting things up for empirical analysis. I've got an underwater camera. I just need a way of marking distance for video in the pool. Might take a couple weeks but I'm curious enough to try this out. Was thinking about those free body diagrams this morning driving into work and your really cool analysis. Not sure i can do that anymore, but clearly you and qbrain can. you might be able pull this off on the deck with two timers, a tape, and maybe a third person timing and marking off the positions. Wondering about the angle/height of the swimmer, although i think you and others have pretty proven diving as straight out as possilbeis is the best approach. There are scanners that can collect position data very accuratley, but im not sure if they would work on a subject moving through the air.

RE: Physics and the racing start.

Former Member — Mon, 26 Nov 2012 13:52:32 GMT

I didn't want to go there. I think you are missing out on all the fun. Once the swimmer hits the water, he has too much control for a simple model to apply. This could be your life's work! but I'd guess that and empirical approach would be much easier. Agreed. Allen needs to go try different start techniques at stop pestering us with mathematical justifications for one side or the other. When he gets to the 15M mark faster than Fort, he should stick with that approach.

RE: Physics and the racing start.

ande — Mon, 26 Nov 2012 12:20:27 GMT

Why jump straight out from the start? you want mostly OUT trajectory with some up It's pretty impossible to "stall out" if you dive slightly more up Wind resistance won't slow you down that much after only 8 to 12 feet I think it's a bad idea to jump "slightly down" water is 800 times thicker than air, it's better to have more air time you want to Enter the water in one hole like you were diving through a ring instead of smacking flat "more effective double-leg kicks are executed before surfacing." = SDKs "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." The truth is vectors and trajectory which could be dectected by a series of pressure plates on a block wired to a computer to determine what great starters actually do durining their starts instead of what they think they do or what coaches say they do or should do. Physics is always right. Sometimes coaches just believe an assumption (about swimming) to be true or better rather than experiement. Have a great set position. Hips high Schoeman says keep your hips high, makes sense because the higher your hips, the higher your center of gravity. Lean slightly back while holding the block (create a plyomentric effect) you'll notice some great starters like cesar cielo, swing their back leg up while still attached to the block which raises their center of gravity the most important variables for 15M speed are: + an explosive start great jump & dive, + a clean entry, (proper angles, an ideal arc, not too deep not too shallow) + a great streamline, + lean mass, (heavier swimmers (but still lean and strong) glide further faster than lighter ones) + fast SDK & flutter, + super break out & + fast swimming I'm NOT sure if jumping straight out is faster, than mostly out with some up I think swimmers can't create as much "UP" force doing a track start as they can with both feet forward. The track start increases stability on the block and decreases "block time" by enough to get to 10 or 15 meters faster. "ït is not a good start if it doesn't give you a red chest" ouch for your chest and time. common sense isn't always sensible What is sensible, is the more starts you do with measurement, testing & feedback, the better and faster you will become. It is a skill you can develop and improve. There are best practices for racing starts. They are based in science and fact. HOW? + Watch video of the greatest starters in the world, + Copy their technique + video your starts and watch them in slow motion, (above the water from the side and underwater from entry to break out) + Time 10 & 15 meter sprints + Get one on one expert instruction Anything you do and measure, improves. The problem is that coaches aren't getting their swimmers to do the right stuff or measuring it accurately or enough. Ande

RE: Physics and the racing start.

Allen Stark — Mon, 26 Nov 2012 11:14:12 GMT

Okay, I'm sending this to Mythbusters. They already tackled swimming in syrup vs. swimming in water. Woohoo :banana:. After that they can answer the age old question of "how fast can you go in a pool filled with diet coke wearing a tech suit made of mentos.":bolt:

RE: Physics and the racing start.

Former Member — Mon, 26 Nov 2012 10:11:39 GMT

How are you going to calculate the transfer of velocities from air to water given different entry angles? Don't be silly. It's very easy. You take the coefficient of the horizontal distance and multiple it by the amplitude of how much force is being applied at the moment of inertia.

RE: Physics and the racing start.

Former Member — Mon, 26 Nov 2012 09:55:32 GMT

First, I think Pete and Allen are over simplifying things. If you are ignoring water induced drag, then you are just discussing jumping. In my most humble opinion of course :angel: I hadn't looked closely enough at Peter's analysis.If it leads to the conclusion that the 0 degree starter goes further in the air it must be flawed. It is possible for a 0 degree starter who creates significantly more force when propelling themselves at 0 degrees compared to 30 degree to go further. I couldn't get Pete's applet to work for me, so I just stole his numbers and plugged them into the projection formulas. Given Pete's numbers, you are correct. a = angle (0 or 30 degrees) v = velocity (3.5, 3.8, 4.55 m/s) t = time g = gravity (9.81 m/s^2) y = vertical distance (or height) x = horizontal distance sin(30) = .5 cos(30) = .866 sin(0) = 0 cos(0) = 1 y = vt sin(a) - .5gt^2 x = vt cos(a) The block is .75m tall, so solve for -.75, or when the swimmer hits the water. 30 degrees @ 3.5m/s solve for t: -4.905t^2 + 1.75t + .75 = 0 t = .608 3.5(.608)(.866) = 1.843m 0 degrees @ 3.8m/s solve for t: -4.905t^2 + 0t + .75 = 0 t = .391 3.8(.391)(1) = 1.4858m 0 degrees @ 4.55m/s t = .391 4.55(.391)(1) = 1.77905m How are you going to calculate the transfer of velocities from air to water given different entry angles?

RE: Physics and the racing start.

jaadams1 — Mon, 26 Nov 2012 09:04:50 GMT

LOL! I was obviously :bed:when I posted that. .60 Nice! 0.60 is better than 6.0 for sure! :) I'm pretty consistent with 0.66-0.70 for my reactions at a few pools I've swam at that actually had the technology to record these times. One good drill :D for speeding up your reaction time is to get a good friend (like Speedo) to stand alongside you while on the blocks with a kickboard...in a baseball stance. At the start signal, your friend swings the kickboard, and you're hopefully out of the way before impact!! :afraid: Doesn't take long to get the picture!! (we did this in college a few times for fun)

RE: Physics and the racing start.

The Fortress — Mon, 26 Nov 2012 08:53:29 GMT

Did any officials ask you if you were going to go or not? :bolt: LOL! I was obviously :bed:when I posted that. .60

RE: Physics and the racing start.

That Guy — Mon, 26 Nov 2012 08:41:29 GMT

I had one reaction time in Omaha that was 6.0. Did any officials ask you if you were going to go or not? :bolt:

RE: Physics and the racing start.

Former Member — Mon, 26 Nov 2012 08:12:21 GMT

Here is a photo of Anthony Erving's start at US trials: www.zimbio.com/.../Anthony Ervin Although he is doing a "horizontal" start you can't get your body into that position just pushing forward at 0 degrees. He must have pushed up at around 25 or 30 degrees.

RE: Physics and the racing start.

Allen Stark — Mon, 26 Nov 2012 07:58:48 GMT

Not quite. The reduction in velocity is due to the vertical component of the force that the legs provide acting against gravity. You can't consider projectile motion until after you have left the blocks and no other forces are being applied to the swimmer. I'd play with the projectile java applet a little bit. The maximum distance is 45 degrees ONLY when there is no difference between the starting height and ending height. If your starting height is higher than your ending height, the maximum distance will be less than 45 degrees. I can prove this with the equations but playing with the applet would probably be easier to visualize. Also, ballistics makes the assumption that the exit velocity of a gun barrel is the same no matter what the angle. For a relatively small mass accelerated by a relatively large force, this is a valid enough assumption for engineering work. Consider however the case of a canon that fires a cannonball with the force of 1g. If the barrel is pointed straight up, the cannonball will never exit the barrel. If the barrel is pointed horizontally, the cannonball will exit so long as it can overcome the friction forces inside the barrel. Thanks,that makes sense.

RE: Physics and the racing start.

The Fortress — Mon, 26 Nov 2012 07:49:22 GMT

AHA!! A challenge yet again!! Indianapolis. You'll have to enter the 1650 with the same entry time as me so we can get seeded together (only chance of men/women together), and then we'll race it to the 15 meter mark AND compare reaction times off the blocks. I do start the 1650 the same as my 50/100, just don't normally sprint to the 15, but in this case I can make an exception. Now, can we get you to enter the 1650? :D What?! Waste a nationals entry on the 1650? I will stick with the much harder to place in sprint events. :D I had one reaction time in Omaha that was 6.0. I was speaking of my own competitors (I'm sure there are young fast big dudes who can beat me), though I am up for the 15 meter challenge! Non-free.

RE: Physics and the racing start.

jaadams1 — Mon, 26 Nov 2012 07:18:16 GMT

As a non physics person, I have nothing to offer EXCEPT I can beat James Adams off the blocks. I use a straight forward track start and no competitor beats me to the 15 meter mark. So I'm not changing. :) AHA!! A challenge yet again!! Indianapolis. You'll have to enter the 1650 with the same entry time as me so we can get seeded together (only chance of men/women together), and then we'll race it to the 15 meter mark AND compare reaction times off the blocks. I do start the 1650 the same as my 50/100, just don't normally sprint to the 15, but in this case I can make an exception. Now, can we get you to enter the 1650? :D