# How does kicking work?

How does the flutter kick, as in the standard
crawl stroke, produce forward propulsion? An
oscillatory up and down motion, somehow creates
a net force. It's a mystery to me. And how
do flippers amplify that effect?
PS And why am I the slowest swimmer in the pool?
PPS Are the feet supposed to break the surface on this kick?
--
Rich
The same way a fan blade moves air; the surface is at an angle with the fluid.
Flippers increase the area.
Too much time on the computer and not enough time in the pool.
Only if you are trying to fly.
Unlike bacteria, we live in a high Reynolds number world. Here is a link to a fascinating article describing a world where the flutter kick would be useless.
Jerry
Unlike bacteria, we live in a high Reynolds number world. Here is a link to a fascinating article describing a world where the flutter kick would be useless.
pbrody/reynolds/lowpurcell.htm l
Don
One reason I'm so fast is because I have stator blading on my legs to accelerate all the water in the aft direction.
Bret Cahill
This may be correct, in principle, but you have work to do to show that a flutter kick operates like a propeller.
ouch! The truth hurts...
Huh?
-- Rich
Or a wing or anything else that produces a force at roughly a right angle to the fluid flow.
Easy to show; tie/tape/glue a bunch of yarn to your legs and feet and videotape the flow.
Think about how you fan yourself on hot days with a piece of paper or cardboard, or in a pinch by flapping your hand. In all cases you are oscillating something in a plane perpendicular to the desired air flow, yet you are generating flow against your face.
Not if I'm in the pool, too.
Have you ever tried to propel yourself by feet alone, using one of those foam boards they give beginning swimmers? It's an incredibly slow form of propulsion. Maybe (certainly) competitive swimmers get a lot more thrust out of their flutter kick than I do, but I would guess that the hands and arms generate most of the thrust.
An exception might be the butterfly, where the entire lower body is flapped.
- Randy
It's difficult to quantify, and of course there are individual variations, but typically quoted figures are...
for Front Crawl, Back Crawl, and Butterfly in the range from zero to 15-20%;
for Breaststroke, anywhere from 25% to 75%.
In the first (three) case(s), the higher numbers are for good kickers while sprinting (anything longer than a 200 is not a sprint; swimmers doing such a race may kick a lot but exercise physiologists would suggest it is probably not the best strategy).
In the case of Breaststroke, the wide range follows from the great individual variation in stroke; and being at one or the other end of this range is no bar to success - or even supremacy.
If you were pidgeon toed you might be able to recoup some of the vertical movement of water wasted in kicking.
Bret Cahill

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