I was fascinated by this article. I really enjoyed reading the physics of the problem, but was amazed no one mentioned low-level falls from older elevator’s, or the braking system in all elevators since 1950.
I saw The Bad Astronomer’s article on the subject and Cecil’s 1983 article on the subject and they both spoke purly of the physics.
In a low level elevator fall, putting yourself on the floor of the elevator is the best way to avoid, serious injury. The impact distributes the force around your entire body lessening the injury. However, in modern times, this could never happen because the brake systems designed in the elevator’s are based in a system where should the cable snap, the mechanical system kicks in and the brakes deploy from the weight of the elevator. As long as the cable is hooked up, taking the weight o the elevator the the lever brake stays shut. My brother has been working for OTIS for 20 years and is currently out of San Bernardino.
He and I have discussed this at length, and aside from the braking system, and mechanical lever’s most elevator’s are made without cables and look like this , this , or this.
So…what if the elevator started falling when it was only on the second floor?
Less chance of injury?
We now know what happens if the elevator plummets with cables intact but what if they were to somehow break? I was told by an elevator installer that if that should happen, the elevator, which is unevenly weighted by significant amounts from one side to the other, would tip if the cable snapped, thus lodging the elevator in the shaft to prevent it from falling to the ground. Perhaps he was pulling my leg. I don’t know. Anyone?
Of course it’s impossible to tell exactly when the elevator is going to hit the bottom since by the time you realized it it would be too late to do anything about it anyway. It’s not like you can see it approaching the bottom of the shaft.
Not to be a total party-pooper, but since most elevators these days are hydraulic, the fastest they fall is, well, how fast they normally proceed down. They are supported by hydraulics underneath the car, instead of hanging from cable(s).
I am sure there are some old-fashioned cable elevators out there, but not in big modern office buildings like you see in the movies all the time.
Just my two cents.
Actually SmartAlec, if you look at his last three cites, they are all of hydraulic elevators.
Eeek. I hate elevators. What I want to know is how often do elevator accidents like that happen?
And if everything goes totally wrong. The lift does a freefall to the bottom. And you’re really lucky with the timing of the jump.
Wouldn’t you then bang your head really hard into the roof?
i can’t imagine that the elevator just goes “BANG” without getting at least a bit squashed.
in so case i’d guess that instead of stopping “on your feets” at 100 fet per sec, you’d bang your head at the speed of 105 fets pr. sec.
Not much better IMO.
The worst has already happened. I read that the elevator cables were cut when a plane hit New York’s Empire state building back before I was born.
The occupant was saved by two things.
One, terminal velocity is reached quickly when you’re squeezing a column of air in a closed elevator shaft. Thus gravity can reassert itself to keep you from floating in mid-box and keeps the box from free falling.
Two, several stories worth of cables were quickly stacked at the bottom of the shaft to soften the fall.
You don’t want to jump as it’s safer to be flat on the floor when the box hits bottom. If you’re in midair your body will quickly collide with the floor when the floor stops moving.
Back to the original subject…if you jump, you also risk smashing your head against the top of the (still falling) elevator. This means you get a concusion, then you get slammed to the ground when the elevator reaches the end of its descent.
I can’t believe I’m saying this, but Cecil seems to have missed the boat on this one.
A couple of points that haven’t been addressed:
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If an elevator were to be in true free fall (that is, if there were no air resistance or any mechanical contact slowing down its fall, so that it moved downward at 1G), the occupants would be weightless and there’d effectively be no “up” or “down”. (Of course, this situation would abruptly change when the elevator reached the bottom of the shaft.) Fortunately, this situation is practically impossible.
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If an elevator were descending at a terminal velocity of, say, 100 feet per second (fps), jumping just before it hit bottom (that is, timing your jump so that you’d be in the air when the elevator hit) would do you no good – and not because you can’t jump fast enough to take away sufficient velocity; in fact, by jumping you’ll increase the velocity at which you encounter the floor.
Consider: just before the elevator, moving at 100 fps, hits, you jump up, timing it so that you are at the apex of your jump the instant the elevator hits. At that moment, your body is motionless relative to the elevator, but is still hurtling toward the ground at 100 fps. Add to that the slight amount of velocity you gain from gravity in the fraction of a second before you hit the floor.
Imagine that the elevator is a platform with an open top, but still descending at 100 fps. Imagine also that you’re actually capable of jumping with a velocity of 100 fps. So before the platform hits, you jump. At the moment of your jump, you’re rising at a rate of 100 fps – relative to the platform. But relative to the shaft, and the world at large, you’re not rising at all; you’ve only cancelled out your downward velocity. But not for long, for you immediately begin falling. Still, relative to the platform, you’re still rising, but at a rate which decreases by 32 fps/second, so that in just over three seconds you’re at the apex of your jump, about 156 feet above the platform, motionless relative to the platform but moving at 100 fps relative to the shaft. If the platform hits bottom at that moment, you’ll suddenly be moving at 100 fps relative to the platform, and will still have a 156-foot fall on top of that. So you’ll hit the platform approximately 1.3 seconds later, at a velocity of about 141 fps. That’s no good.
Of course it should be noted that:
a) If you could jump off the platform and grab a convenient handhold on the shaft, you’d be okay. However, since this is my thought experiment, there aren’t any handholds on the shaft. In fact, the shaft is slippery as an eel.
b) A person capable of jumping up at 100 fps should also be capable of withstanding an impact of 100 fps. So his best bet would be to flex his knees and await impact.
I’m not a physicist, and my calculus is rusty, so I’m sure somebody will correct me on this.
baldwin said exactly what was on my mind while reading it, although my reasoning was slightly different (well, mostly that I had no reasoning, but I know that when you jump you are exerting additional downward force upon the elevator that is already hurtling downward in order to propel yourself upward. Thus it’s not simply [elevators downward velocity] - [your upward velocity] = pancake). I hadn’t considered the effects of free fall until it was mentioned here and I remembered what it actually meant.
However despite ignoring nearly all of the physics involved, Cecil’s end conclusion was correct.
Baldwin, the problem with your analysis is that if you wanted to minimize your impact speed, you would not “jump up, timing it so that you are at the apex of your jump the instant the elevator hits”. Instead you would, as the letter to Cecil says, “jump into the air at the moment of impact”. This will have the net effect of slowing your impact speed, and if you can jump up so that your initial speed is equal to the elevator’s terminal speed, you would be fine. Of course, the problem is that you can’t do this for any realistic terminal speed. As Cecil said.
Virtually never. You are safer in an elevator than going down or up the stairs. If fear of falling is why you hate them, you have to accept it as an irrational fear.
Achernar, let me think… Okay, you’re right. In the scenario I used, if you could jump upward at 100 fps at the very instant of impact, you would neatly cancel out the downward velocity. Why, you’d be a fool to jump before that! But of course the net effect is that you’d be absorbing the enormous deceleration involved with your super-powerful leg muscles, instead of with the abrupt and messy collapse of your bones and tissues. If you could only exert enough force for, say, a 50 fps leap, you’d still have 50 fps of impact to deal with. In either case, you wouldn’t be leaping into the air at all; your feet would stay on the floor. Cecil’s description implied an actual leap, with some air below one’s feet (or at least that’s the meaning I took from “a leap of Nureyevian proportions”), in which case I stand by my half-baked analysis.
Anyway, a person of normal strength is screwed. Good thing elevator accidents don’t happen often; I’m sure you’re more likely to get killed falling off a fire escape. The movies can’t seem to get away from the idea that elevators are suspended from cables, which could break any old time.
I hate to throw a boomerang in the mix here, but your assumptions minimize a central factor. Friction. Elevator’s don’t hang, they rest in nice little tracts. Even the older ones didn’t hang. the brake is in the track, the emergency brake is on the elevator. So even if you have a modern elevator, with a cable, and you cut the cable, you’d only fall a few feet before the brake would catch the elevator. Assuming the brakes are sheered off by hampsters, both in the track and on the elevator, the friction and unbalance of the box itself would forebode the elevator from ever reaching terminal velocity.
Sure it would. It’s just that the terminal speed would be lower than it would be without the tracks. I get the impression that 100 feet per second is pretty fast for a shaft-sliding car, but I don’t know what’s actually reasonable.
In my family (a largish group of folk) there is one elevator accident. My uncle and another guy at a cement plant, early '60s. The elevator actually did free fall. A lot of body damage was caused by the collapsing elevator car crashing in on them after the impact. (Yet another thing “jump at the last second” folk don’t consider.) The other guy didn’t make it. My uncle spent weeks in a conv. hospital.
First, I used to build elevators. It was an interesting occupation but I fell in love with computers so… career change.
This whole discussion misses one point: the REAL danger in an elevator is not free-fall but runaway up, an elevator getting stuck in full-speed up. The machinery of a cable-type elevator (the only type practical in high-rise buildings, over say, 12 stories) is controlled by a series of relays, more or less first gear, second gear, etc. If the “high-gear” relay should jam, the car (elevator itself) would simply go to the top at full speed. Since virtually all of the safety devices are oriented toward dropping (or speed control), a runaway-up elevator would hit the overhead at full speed (about 25 mph in skyscrapers), bouncing the occupants off the ceiling head first, breaking necks. Even the speed-control safety devices wouldn’t help because it’s not exceeding its design speed. But when it runs out of hatch (shaft to civilians), there are large I-beams to support the machinery at the top. These would be what stops the car. Suddenly.
Of course, then you’ve got to wonder about what that collision at the top did to the free-fall safety devices…
Runaway-down wouldn’t be so life threatening. You’d be likely to break legs but compared to a broken neck…
If you REALLY want to worry about such things, at least worry about the real danger.
Like I asked, what if it was falling from the second floor?