Drafting

Originally posted by knelson Actually that is exactly what we are looking for. It tells us that a swimmer passing through the quiescent water will accelerate that water in the direction he/she is swimming. All it tells us is it's possible to draft, though. It tells us some of that swimmer's (or hand's) energy has been transferred into moving the water forward. It doesn't really help answer the question of whether the lead swimmer is helped or hindered by a drafting swimmer, though. I took it as obvious that the swimmer has accelerated some water. What the confetti is entirely unable to show us is how that accelerated water now affects another, similar size/mass, object that is placed in that space. The lone Nascar IS "pulling" air along behind it - which costs some energy. When the draft car tucks in behind that car the drafter now "pulls" a large portion of the tail air instead of the lead car pulling it. This shifts the work (fuel consumption) of pulling that air onto drafter and frees the lead car from that portion of the combined work. In return, the drafter is relieved of much of the frontal resistance which the lead car still labors under. Because the trailing end of a swimmer is quite tapered, the amount and nature of the tail eddys and turbulence is quite different than that of the rather blunt ended cars. A bit like the difference between the tail end of a Kayak vs the tail end of a rowboat. While a swimmer can get close enough to benefit from lower frontal resistance, I think the swimmer cannot get close enough to shift the tail resistance away from the lead swimmer.

Originally posted by knelson Actually that is exactly what we are looking for. It tells us that a swimmer passing through the quiescent water will accelerate that water in the direction he/she is swimming. All it tells us is it's possible to draft, though. It tells us some of that swimmer's (or hand's) energy has been transferred into moving the water forward. It doesn't really help answer the question of whether the lead swimmer is helped or hindered by a drafting swimmer, though. I took it as obvious that the swimmer has accelerated some water. What the confetti is entirely unable to show us is how that accelerated water now affects another, similar size/mass, object that is placed in that space. The lone Nascar IS "pulling" air along behind it - which costs some energy. When the draft car tucks in behind that car the drafter now "pulls" a large portion of the tail air instead of the lead car pulling it. This shifts the work (fuel consumption) of pulling that air onto drafter and frees the lead car from that portion of the combined work. In return, the drafter is relieved of much of the frontal resistance which the lead car still labors under. Because the trailing end of a swimmer is quite tapered, the amount and nature of the tail eddys and turbulence is quite different than that of the rather blunt ended cars. A bit like the difference between the tail end of a Kayak vs the tail end of a rowboat. While a swimmer can get close enough to benefit from lower frontal resistance, I think the swimmer cannot get close enough to shift the tail resistance away from the lead swimmer.