這個標誌是危險的宣傳，它提升了瀑布暗流的神話。 如圖所示，在此瀑布中，任何其他瀑布中，甚至在海灘上都不會出現暗流。 除少數極端情況外，唯一會在大壩和水力發電廠的排水管附近找到類似水流的地方。 由於在池底沒有出口流出，因此自然界中不容易發生這種現象。 在瀑布底部或附近漂浮的困難是由於與水中混合的空氣有關的浮力的變化，而不是向下的水流。
實際上，該瀑布的流入和流出都在水池的表面。 這意味著最強的水流在水面上，最弱的水流在底部。 在一年中的大部分時間裡，幾乎沒有地下暗流。 如果您沒有在頂部看到它們，它們就不會隱藏在底部。
當河流中有大量的水流過時，瀑布的力量會在水池表面形成一個小的凹陷，導致水向該方向流動。 多數反彈並產生從池中流出的水流。 有些也從瀑布流回到瀑布下的凹陷處。 這些僅表面水流。 由於水只能從較高的高度（例如，地面）向下流動，因此它們不會在池中深處延伸。
因此，要逃開這些水流的正確方法是在它們下面游泳。 表面水流將您反覆拉出來，而不是暗流。 因此，要逃脫，您需要向水底下游泳。 這是應該在標誌上顯示的消息。 逃脫離岸流方法相同，在這裡也適用。卡住在垂直的水流中游泳，不要跟它對抗。但要在瀑布前游泳，是有悖常理的。中心的水流將帶您離開瀑布跟水池。這些訊息應該要標示在告牌上。就像在海灘告示牌上一樣，有標示如何逃開離岸流，所以這裡也應該有標示如何逃開瀑布中的水流。 但相反地，這個標誌沒有提供任何有用的訊息，實際上還具有誤導性。 這是進行水安全教育的尷尬方式。
附註1：這僅適用於一個水池範圍。 在河流中，整個橫截面都在流動，由於摩擦因素使其底部水流動仍然較慢。 而表面的水流動得更快。
附註2：颱風過後，當河流太大而超過水池的承載能力時，以上這些規則將失效。 這並不重要，因為對於任何理智的人來說，顯然無論如何在颱風過後是不要進入溪河裡。
This sign is dangerous propaganda which promotes the myth of the waterfall undercurrent. Currents as depicted in this picture do not occur in this waterfall, any other waterfall, or even at the beach for that matter. With a few extreme exceptions, the only place you will find currents like that are near drainage pipes for dams and hydroelectric power plants. It's not a phenomenon that can occur easily in nature because there is no outflow at the bottom of the pool. Difficulties with staying afloat at or around the base of the waterfall is due to changes in buoyancy related to air mixed in the water... not downward currents.
In fact, the inflow and drainage for this waterfall are both on the surface of the pool. This means that the strongest currents on the surface of the water, and the weakest currents are on the bottom. For most of the year there are barely any subsurface currents at all. If you don't see them on top... they aren't hiding on the bottom.
When there is a lot of water flowing in the river, the force of the waterfall creates a small depression in the surface of the pool, causing water to flow in that direction. The majority bounces out and creates a current flowing out of the pool. While some also flows back to the depression under the waterfall, typically from the side. These surface-only currents. They do not extend deep in the pool as water can only flow downward from a higher elevation (eg, the surface).
Therefore, the proper way to escape these currents is to swim under them. Surface currents are pulling you out, not undercurrents. So to escape you need to swim down. The same method for escaping a ripcurrent will also work here. Swim perpendicular to the current you are stuck in, not against it. It's counterintuitive, but swim in front of the waterfall. The current in the center will take you away from the waterfall and out of the pool. This is the message that should be on the sign. Just like at the beach there are signs explaining how to escape a rip current, there can be signs explaining how to escape a back current in a waterfall. Instead this sign provides no useful information, and is in fact misleading. It’s an embarrassing way to conduct water safety.
Note: This only applies to pools. In a river the entire cross sectional area is flowing, although it's still slower at the bottom due to friction. Surface water moves faster.
Note 2: After a typhoon when the river is so large as to exceed the carrying capacity of the pool, these rules breakdown. It's not important because to any sane person, it's obvious not to go into the river after a typhoon anyway.
buoyancy force 在 What is Buoyancy? | Physics | Don't Memorise - YouTube 的推薦與評價
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