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Impulse of Hitting Salt versus Fresh Water
Name: Joann
Status: student
Age: N/A
Location: N/A
Country: N/A
Date: N/A
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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Update: June 2012
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