
The Physics of a Firefighter's Window Catch - alex_young
https://www.wired.com/story/the-wild-physics-of-a-firefighters-window-catch
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lolc
What is ignored in the article is that a large part of the momentum was
absorbed by the wall the victim must be assumed to have crashed against. Since
the firefighter was anchored to the window sill, it was enough for him to hold
on to the victim to turn the momentum towards the wall.

Still the firefighter needed a lot of force to hold on to the victim through
the tight turn. If his grip hadn't been good, he couldn't have done that. That
is very impressive.

Edit: By the looks of it the victim was held at the legs. We can expect a bad
concussion.

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yk
"Turning momentum against the wall" needs actually more force than just
stopping the faller. If the faller initially falls with momentum -p z (where I
will denote the unit vectors of the coordinate system with x, z, and p is the
magnitude of the momentum) and turns that into p x, then you need an average
force of Favg=deltap /t= sqrt(2)p /t, while just stopping would only be
Favg=p/t, where deltap is the total change in momentum and t is the duration
of the stopping.

The reason for that is, that momentum is a vector and so you need to supply
force in along each of the coordinate axis individually.

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LorenPechtel
You're assuming a 90 degree turn. It doesn't take a 90 degree turn, however--
they were probably still heading mostly down when they struck the wall. The
wall (and the falling person) would absorb most of the impact. Not good for
the faller but far better than keeping on going.

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overcast
Just have a look at the comments of the video on YouTube. That sums up why I
no longer visit Reddit, and turn off comments on most sites. Impressive catch
though!

[https://www.youtube.com/watch?v=eqHloZxSeGo](https://www.youtube.com/watch?v=eqHloZxSeGo)

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qrbLPHiKpiux
Yes, but there have been a few gems (not sarcasm) that I find sifting through
all those comments that I've found very useful. It's like digging through shit
to find something valuable.

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overcast
Just what I want to waste my time doing.

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dmurray
Another way to look at this: it takes about as much work to stop someone
falling from 3m as it does to launch them 3m in the air. So if you can stop
the guy falling, you could instead throw him into the air to the same height.
It's not quite that simple (different muscle groups, etc) but a good
approximation.

Flinging 50kg to a height of 3m above the release point seems a little high.
I'm a fit adult male, although neither an athlete nor a fireman, and I can
manage about 15cm. So I think friction is doing a significant part of the work
here, likely between the fireman's clothes and the wall or window sill.

Still an impressive catch of course!

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salty_biscuits
Or carrying them up a flight of stairs on your back. I think peak power is
more important than work here. The peak power to throw someone 3 metres into
the air is ludicrous, but arresting a fall over a (slightly) longer time
period, with bones and ligaments taking the peak power instead of muscles are
what is going on.

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saagarjha
> with bones and ligaments taking the peak power instead of muscles

That's kind of an odd way of phrasing it; I would have said something along
the lines of them providing the upwards force through tension rather than
bringing power into the discussion.

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salty_biscuits
It's the time derivative of work, seemed natural to me. Also muscles use rate
limited chemical reactions to move, so it is a reasonable assumption to model
them as power limited (with different regimes for different metabolic
mechanisms). So when talking about the limits of what a person can do with
their muscles, power limits seem important.

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mongol
I thought the article would be about how you get a grip that don't slip when
the person flies past you.

