1. Also, you can think of it like water poloball. If you take a water polo ball in the water, put your hand on it and press it down, you get pressure up against it that come up.
你也可以想象成一只水球，如果你拿个水球放在水中，把手放球上向下压，你就会得到上升的反作用力。
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2. Also, you can think of it like water poloball. If you take a water polo ball in the water, put your hand on it and press it down, you get pressure up against it that come up.
