Quick Physics Question

EDIT: I'm bored. Let's make this the official Physics Thread and see what happens :B

The person falls from a flying ship over the sea. They try to use magic to slow down their fall so they don't break every single bone in their body. They run out of strength to maintain the spell when they are x feet away from the water, fall on a 4 foot long fish, and kill it while suffering no more than severe bruises.

If the above scenario is at all possible (not considering the presence of magic), what is x?

edited 21st Nov '10 6:52:29 PM by snowfoxofdeath

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You can't kill the fish without killing yourself. The force exerted by the falling body on the fish is equal to the force exerted by the fish on the falling body. Enough to kill a large fish is probably more than enough to kill a human so...sorry. Landing on an already dead fish in the ocean, though, and sufferring no more than bruises is plausable I'd say to at least thirty feet.

Equal force ≠ Equal effect. You forgot to consider such variables as the difference in toughness and elasticity between human and fish tissue. Still agree on the overall effect tho. If you are going to right out fall on a fish and kill it, you won't exactly get out well yourself.

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How about a severely broken leg?

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When you're in deep water, any severe injury is a death sentence - you won't be able to keep yourself afloat for long. Injuries give you super drowning skills.

edited 13th Nov '10 10:26:42 PM by Lessinath

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Also, the drag from passing through water doesn't increase proportionally with your speed. It is proportional to your speed to the fourth. Crashing into the water twice as fast will do 16 times as much damage.

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Only 4 times as much energy is involved in the collision though.

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About 80 feet (24m) is the highest your average human can survive a fall into water. And as for killing a fish upon impact... well obviously your character is heavier than the fish, which means the impact upon the fish will be greater than the returned force (as dictated by Newton's 3rd Law).

So it is quite odd... but it is feasible.

Note, if your character were dropped from this height (assuming static position ~ i.e they don't already have a downward speed), they will impact the surface of the water at 49 miles/hour (78km/hr) ignoring for air resistance. It is advisable to work within these limits.

edited 15th Nov '10 1:19:39 AM by LanceManley

Education without values, as useful as it is, seems rather to make man a more clever devil. ~ C. S. Lewis

Another Physics question! I don't want to steal the spotlight from Mr/Ms OP here, but I feel it would be silly to post another Physics question thread if there's already one.

Would it be possible for a planet to be essentially identical to Earth (carbon-based life, Nitro/Oxy atmosphere, Humans) but with slightly less gravity (I'm talking, if Earth gravity was 1, this planet is .95)? Would .95 be a big enough difference in gravity that it would effect evolution in extremely different ways? How would Earthlings fair on this planet? Would they be able to run a teensy bit faster or stand a little bit taller?

Yes, all you need to do is decrease the diameter or the density by ~5% (the latter is easy - Earth is unusually dense compared to other planets whose density has been measured).

I doubt such a small change would make a breathable atmosphere impossible.

Hard to say. There are so many factors, even the distance to the moon may effect evolution through the tides. But my guess is, no, it would not effect evolution so much.

I think we'd adjust with no problems.

Yes, but you'd hardly notice the difference. At first, you would notice that you were a little lighter on your feet and would be more likely to injure yourself accidently until your body readjusted. You would probably be taller because your spine would be less compressed, but since 1g => 0g yields up to maybe 1 inch (25mm) taller, we're talking 1mm (<1/16") taller here.

However, having a combination of luck and will to live can make you a Bad Ass in Real Life survival situations. Survival often depends on having a cool head and how far you are from shore - but without rescue available, recovery from severe broken bones would be much rarer than it is statistically, since most people that survive are rescued.

edited 19th Nov '10 7:50:01 AM by FrodoGoofballCoTV