So I've just been watching a TV program where two people open a canal lock, and it occurred to me: aren't you pushing against the entire pressure of the river when you push the lock doors open? Why is this possible, shouldn't it be far more force than people can manage?
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4$\begingroup$ The lock gates are opened and closed when the level of water is the same both sides. To achieve having the water level the same slices and paddles are used. abcboathire.com/aguidetooperatinglocks.aspx $\endgroup$– FarcherCommented Jun 4, 2018 at 17:36
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1$\begingroup$ It depends on which way the locks open. To open them in the flow of water is very easy. To open them, against the flow, not so easy. Most are open either when water is level, or when they are with the flow of water. $\endgroup$– John AlexiouCommented Jun 4, 2018 at 17:53
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1$\begingroup$ A (related) question often used to probe student understanding of static pressure is to draw two proposals for creating a lake with a dam. Both have the same depth and width but one is much on a shallower basin and so extends much father upriver. You ask "Which dam feels the larger static force from the trapped water?" The answer is—of course—"They experience the same static force.". $\endgroup$– dmckee --- ex-moderator kittenCommented Jun 4, 2018 at 18:51
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2$\begingroup$ @Farcher I'd suggest fleshing out that comment and making it an answer, so the OP can (hopefully) accept it. $\endgroup$– StephenG - Help UkraineCommented Jun 4, 2018 at 21:30
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1$\begingroup$ @JohnAlexiou, Lock gates always open against the flow. That's on purpose. It guarantees that the gate can never be opened except when the water level is the same on both sides. You can infer from that, that it also guarantees that the two gates can never both be opened at the same time. The paddles that allow water to flow around or through the gates at a controlled rate are a different story. $\endgroup$– Solomon SlowCommented Mar 2, 2022 at 18:39
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