Physics of swimming: momentum

[kellyasherrillParticipant]

Hi, Dr. Nebel! Thank you again for creating a nice curriculum for our students. I write with a question/request: My daughter (age 8) is a competitive swimmer, so I often tie principles of physics to swimming. Do you have an example of explaining the relationship of momentum to swimming that does not require advanced mathematics? Most of the videos I have found involve higher level math, and I’ve been less-than-competent with helping her piece together the relationship, for example, between the rotation and angle of her turns to the momentum she has coming off the wall. She understands that the tighter she turns, the more momentum she has off the wall, but she cannot quite explain why – for example – the strength and movement of her underwater dolphin kicks on the start or on the turns affects her momentum. As a practical reason I would love to help her make the connection, she is obviously smaller and not as strong as she will be in even a few years. She enjoys doing 6-10 underwater dolphin kicks on her backstroke start, but she is not quite powerful enough to surface after doing so many underwaters, and she loses momentum before she reaches the top and transitions into backstroke. If she could calculate or feel the point at which she gains, continues the same, or loses momentum on her starts and turns, she will better be able to gauge the right number of dolphin kicks and the best turn rotation at the walls. (I hope this makes sense; I recognize that, to non-swimmers, it may read a bit “Greek.”) If you Google “backstroke starts and turns,” you’ll get a sense of what I’m asking. Thank you!!!

[Bernard NebelKeymaster]

Hello
You raise an interesting question. I swim but I am not a swimmer. I really hope that someone with more knowledge in this area will chime in.
Looking at the problem from an overall physics perspective, however, I question how much of role momentum (the tendency of a moving body to keep moving) actually plays. The greatest resistance to a swimmers forward movement is drag of the water — “friction.” This friction will tend to dominate the outcome, momentum notwithstanding.
Therefore, it seems to me, the focus should be on movements/motions that minimize this friction. That, and on movements/motions that maximize pushing forward. Again, I hope that someone with more knowledge will chime in

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