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# Physics/Falling

Question
My grandma told my sister and I a story about this woman and I think her story is physically impossible. She said she knew some women whose husband was leaving her; so she threatened him with suicide. Her husband left anyway and supposedly she jumped out of her apartment window to kill herself, but (coincidentally) landed on her husband, killing him while not sustaining any injuries. Is that possible? I doubt it because even supposedly soft surfaces will kill you from the right height. Falling into water at 5 feet is safe, at 30 I think you would die. So if something fluid like water can kill you, how could she survive that impac against something solid?

Ps. Why is it that hitting water at certain heights is fatal? I know it is but I thought the surface tension of water is stable - is there a correlation between height and surface tension? If so, how is that possible?

The fatalities you mention from hitting water have nothing to do with surface tension.  They have to do with what most other fatalities have to do with the rate of momentum change (impulse) over time.  If you jump from 33 ft (10 m) off of a high-dive platform, you're moving at roughly 14 m/s, or 31 mph.  If you do the same thing from 100 ft, you're adding three times the energy to your body and traveling at 24 m/s.  But you've seen people hit water, in order to go into the water you have to displace a large amount of water...so people stop in roughly the same distance from those dives.  The stop from the higher dive happens almost as fast, but the momentum change takes it form painful belly flop to fatal belly flop.  The rate of change of momentum gives us the maximum force.

Which brings us to your grandma's story.  Yes, it's possible for two reasons.  One, she may have landed on his head at an awkward angle for his neck, but hit it with a part of her body less suceptible to damage.  That's easy enough.  But if you assume a simple collision, her on his shoulders and transferring her momentum to him, that collision will be "slow" as he accelerates/collapses toward the ground compared to his coming to a stop against a hard and immovable surface.  But, having transferred her momentum to him in the collision, she wouldn't hit the ground that fast.  So it's definitely possible, from either a basic physics or a medical point of view.

Physics

Volunteer

#### Dr. Stephen O. Nelson

##### Expertise

I can answer most basic physics questions, physics questions about science fiction and everyday observations of physics, etc. I'm also usually good for science fair advice (I'm the regional science fair director). I do not answer homework problems. I will occasionally point out where a homework solution went wrong, though. I'm usually good at explaining odd observations that seem counterintuitive, energy science, nuclear physics, nuclear astrophysics, and alternative theories of physics are my specialties.

##### Experience

I was a physics professor at the University of Texas of the Permian Basin, research in nuclear technology and nuclear astrophysics. My travelling science show saw over 20,000 students of all ages. I taught physics, nuclear chemistry, radiation safety, vacuum technology, and answer tons of questions as I tour schools encouraging students to consider careers in science. I moved on to a non-academic job with more research just recently.

Education/Credentials
Ph. D. from Duke University in physics, research in nuclear astrophysics reactions, gamma-ray astronomy technology, and advanced nuclear reactors.