I'm not sure if this is the right place to ask this, but I thought I would ask here as it made the most sense to me.

Consider person A swimming in a pool with water flowing against them at 10mph. They swim at 10 mph hence staying in a stationary position.

Consider person B swimming in a pool where the water is essentially still. They swim at 10 mph moving forward.

Which of these 2 would be exerting more force, if any and why?

My thought is that both of these circumstances are exactly the same (in a basic manner and excluding minute differences).

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    $\begingroup$ Please can you explain the nature of your difficulty? Why do you doubt that your understanding is correct? We do not welcome "check my work" type of questions. $\endgroup$ Jul 13, 2017 at 19:20
  • $\begingroup$ So, my understanding is that in either scenario, the amount of work exerted is the same. In one case you are exerting force to overcome 10mph of force against you and in the other case you are traveling at 10mph which in itself is the force. Hence wanted to make sure it was right? $\endgroup$ Jul 13, 2017 at 19:22
  • $\begingroup$ If you don't doubt that your understanding is correct, why are you asking us for confirmation? $\endgroup$ Jul 13, 2017 at 19:26
  • $\begingroup$ So, I'm not a physics major, this was more a question between some friends of mine and me. My argument is that it should be the same (they say the force exerted in the stationary pool is more). I asked here so that someone who has physics background can back up my answer or, explain to me why my understanding is incorrect if it is? $\endgroup$ Jul 13, 2017 at 19:28
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    $\begingroup$ We do not welcome questions which are only asking for Yes/No answers, because they are not useful for the broader community of users. If you are convinced that your answer is right and your friends are wrong, have confidence in yourself. $\endgroup$ Jul 13, 2017 at 19:38

1 Answer 1


The swimmer is moving with constant velocity, hence zero net acceleration, experiencing zero net force in both scenarios. We can apply the inertial reference frame.

You are describing the swimmer from an external observer's reference frame, hence the two "different" situations.

If you instead describe the swimmer from his own reference frame, then in both situations he experiences the same thing.

In both scenarios, the swimmer can think he is swimming on the spot. In both scenarios, the swimmer can think he is swimming forwards. Both of the swimmer's thoughts are valid, and hence equal.


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