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Name: Bill
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Question:
I have noticed that when watching animals swim, there is a wave in front of them as well as to the sides where I understand there is water displacement and expect it. What causes the wave in front and is there a name for this phenomenon. I am sure it happens in air as well, but I do not see it.



Replies:
Dear Bill,

When swimming as with boating, when the aniaml or boat is moving faster than the wave can travel in the water, the water kind of "piles up" in front of the moving object. This is called a bow wave.

In air this happens when the air molecules "pile up" in front of a jet moving at supersonic speeds. This is also a kind of bow wave but we can hear these moving molecules as a sonic boom.

Thanks for your question,

Martha Croll


Imagine you are in McDonald's play land and in that pit of plastic colored balls. As you walk through the colored balls, the balls in front of you can't get out of the way fast enough So they build up in a pile in front of you. That is the same thing for the bow wave caused by ships. The water in front of the ship simply does not have enough time to get out of the way and it has no where to go but up. This phenomenon happens to an airplane in the air too. It happens to any fixed body passing through a fluid. Streamline designs were invented to allow the fluid (air or water) pass by the body easier. Nature streamlines fish and marine mammals for the same purpose. Ship designers put bulbous bows on surface ships for the same purpose. Submarine designers try to mimic the design of dolphins for the same purpose. The easier the fluid passes around the body The less induced drag, the less energy required to propel the vehicle/body. Sincere regards,

Mike Stewart



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