Anybody good at physics??

Physics - no. Maybe you lost the wt. & worked on strength more, so losing more will not always make you faster.

OK I'll admit it - I do have a degree in physics but found the whole fluid dynamics thing far too hard. Still working high energy experimental physics, but as others said, too many factors involved for swimming fast. I sometimes notice swimmers skin rippling (around the shoulder blades) when they get a strong push off the wall. Losing weight may cause more loose skin, which may cause more resistance. Or what about weight gain, but it is all muscle mass?

Just out of curiosity...if all things being equal, how much could a person improve simply by losing weight. I've been beaten by many people both heavier and skinnier than me, but, almost assuredly, those who beat me have some combination of better technique + better training + better talent. I do think this idea is warranted, for health, life, happiness and swimming faster, even moreso as we age ... I'm really paying attention to my diet and nutrition ... but am not convinced this... and trying to trim down another 10lbs. ...will directly translate into better times for you in and of itself. Focus on nutrition, focus on technique, focus on training and let the weight loss and speed be a by-product, not the goal.

OK I'll admit it - I do have a degree in physics but found the whole fluid dynamics thing far too hard. Therefore instead of becoming a weather-girl I became an accountant! As for the weight-loss, I found that I could easily maintain 130lbs and swim well, but try and get down to 125lbs and the effort, and feeling of weakness just made it not worth it, so it depends on where that 215 lies in relation to your ideal/minimun weight for your body type. You'll likely feel better in training and distance upon losing some weight, but probably not see much difference on a 50.

As for the weight-loss, I found that I could easily maintain 130lbs and swim well, but try and get down to 125lbs and the effort, and feeling of weakness just made it not worth it This is a good point. there is an optimum. Cut too much weight and you will lose energy. Lose a spare tire? yes. Try to reduce weight when you have no body fat? no.

Just out of curiosity...if all things being equal, how much could a person improve simply by losing weight. Is there a formula that could properly express this.... Any thoughts??? My thoughts are: no way. There are too many factors at play here. If your weight decreases obviously you will require less energy to move you through the water from a pure F=ma standpoint. The other factor, though, is how your weight (or body composition) affects your form drag in the water. A higher body fat percentage will make you ride higher in the water, so having that additional weight is not inherently a negative like it would be in land activities like running. So you're kind of working on both sides of F=ma. Lowering your mass will require less force, but it's unclear how much force will be required to overcome drag at your new weight.

My thoughts are: no way. There are too many factors at play here. If your weight decreases obviously you will require less energy to move you through the water from a pure F=ma standpoint. The other factor, though, is how your weight (or body composition) affects your form drag in the water. A higher body fat percentage will make you ride higher in the water, so having that additional weight is not inherently a negative like it would be in land activities like running. So you're kind of working on both sides of F=ma. Lowering your mass will require less force, but it's unclear how much force will be required to overcome drag at your new weight. Not to mention the momentum(p=mv) issue off the starts and turns.While it takes more force to accelerate you off the starts and turns,you maintain your velocity longer with greater mass.

My thoughts are: no way. There are too many factors at play here. If your weight decreases obviously you will require less energy to move you through the water from a pure F=ma standpoint. The other factor, though, is how your weight (or body composition) affects your form drag in the water. A higher body fat percentage will make you ride higher in the water, so having that additional weight is not inherently a negative like it would be in land activities like running. So you're kind of working on both sides of F=ma. Lowering your mass will require less force, but it's unclear how much force will be required to overcome drag at your new weight. I think F=ma is a non-factor in the water. Any of the swim strokes is a cycle of negative and positive acceleration. The negative acceleration comes from drag, which does not strictly depend on mass, although kind of indirectly via body shape like you said. Greater mass is a good thing in the slowing-down phases of the stroke, provided the drag force is constant, because the negative value of acceleration is inversely related to mass. Imagine throwing a ping pong ball versus a golf ball. Which one slows down faster? The flip side of this, of course, is that it's harder to accelerate in the positive acceleration phases of the stroke. But it should be a wash, right?

I have lots of thoughts on this expressed elsewhere. Mostly opinion and hypotheses. I created a similar thread about this last year. Perhaps it could fill you in on what we already discussed... How much does body weight effect swimming speed? - U.S. Masters Swimming Discussion Forums Feel free to add commentary or thoughts to that thread as well.

I think knelson is right. A formula is impossible as there are too many individual factors. For example if your stomach is smaller or equal to your chest size then losing stomach fat might not decrease the cross sectional area of your body moving through the water so your drag could be the same. If weight loss is not done properly it is also easy to lose muscle mass so you could become slower.