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Name: Joann
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Question:
If you jump into a fresh or hard water lake, vs. jumping into salt water, will the impact be harder for one or the same? Does it depend on the height of the jump?



Replies:
The impact you feel is very much due to the height of your fall, but also the shape your body is when it hits. As you fall, you gain momentum. The time over which you lose that momentum to the water (the deceleration you feel) affects how 'hard' you feel you hit. The faster you accelerate negatively, the 'rougher' the impact. If you straighten your body, you will penetrate the water more, and decelerate more slowly (a more gentle hit). If you belly flop, you decelerate quickly, and the impact feels rougher. Where you hit also matters to how you feel -- a head impact feels worse that going feet first. All of these are probably more important factors than fresh water or sea water. That said, the density of sea water is higher than fresh water, and the viscosity is very slightly higher. Therefore, you will accelerate negatively somewhat faster with sea water than fresh. Therefore, the impact will feel slightly 'harder' with sea water than fresh. Another factor is temperature -- water gets more viscous when it's colder, so make sure your ocean and lake are the same temperature when you gather data!

Hope this helps,

Burr Zimmerman



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