Naked Science Forum
Non Life Sciences => Physics, Astronomy & Cosmology => Topic started by: @_ammara on 30/09/2011 12:01:02
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@_ammara asked the Naked Scientists:
If you're in a falling, crashing elevator but you jump before/during impact, will you survive?
What do you think?
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It would make absolutely no difference !
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As the elevator accelerates down the lift shaft it converts gravitational potential energy into kinetic energy. The same happens to you within the elevator. As you approach the bottom of the shaft if you could jump with all the energy that you had gained in the fall you could theoretically survive but there are two problems with this. You cannot jump with that much energy and even if you could you would hit your head on the ceiling of the elevator. Either way you would not survive.
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No, the elevator and you move in a downward direction, lets say 33 meters a second, just before hitting that floor. So you would need to apply the opposite 'force' to your jump, if going straight up, making you seem to 'stand still' relative the ground. I know that people have survived high falls though, by angling their downward 'force of falling' into a perpendicular at the hit, like rolling, but then they had a slope helping them out too as I remember it.
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It would actually make a slight difference, but you would need to know precisely when to jump, and even if you did jump at the right time, it's unlikely you would survive.
You would be able reduce your velocity slightly by jumping. As the elevator has a much greater mass, you would be able to accelerate relative to the elevator so that your velocity would be (slightly) less than the elevator when it slowed down rather suddenly.
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It would actually make a slight difference, but you would need to know precisely when to jump, and even if you did jump at the right time, it's unlikely you would survive.
You would be able reduce your velocity slightly by jumping. As the elevator has a much greater mass, you would be able to accelerate relative to the elevator so that your velocity would be (slightly) less than the elevator when it slowed down rather suddenly.
That sounds about right. The odds of jumping at the right time would be low, and if you timed it wrong, you'd hit the ceiling and then get squished.
The survival expert advice is usually to lie down flat so that the force of impact is spread over your body better.
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I think they covered this in a Mythbusters episode with their scientific-ish approach.
2004 (Season 2), Episode 9 "Elevator of Death".
Here is a summary of the episode. (http://dsc.discovery.com/fansites/mythbusters/db/science/jump-in-falling-elevator.html)
Acceleration was reduced slightly, but timing has to be perfect. And, the end result was still at least severe body damage or death.
Think of it this way. If you could jump as fast as free-fall, say on a basket ball court, then you would suffer severe injuries when you landed again.
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The problem is that with the jump, a person should accelerate up exactly of the same amount it would accelerate because of the elevator collision with the ground...
Syhprum is right.
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Think of it this way. If you could jump as fast as free-fall, say on a basket ball court, then you would suffer severe injuries when you landed again.
It may be less to do with acceleration and more to do with velocity. Because it has to displace a lot of air in an enclosed shaft, the elevator probably reaches a terminal velocity fairly quickly, so you and the elevator are not likely to be in free-fall.
By jumping (at just the right time) you will subtract your maximum velocity from the elevator's velocity, so your net velocity on impact will be slightly reduced (not that the outcome will be much different).
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The problem is that with the jump, a person should accelerate up exactly of the same amount it would accelerate because of the elevator collision with the ground...
Syhprum is right.
I think that would be true in free-fall, but in this case there is a terminal velocity.
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if your worried about this i have two ideas
make emergency brakes for an elevator
or (may not work as well)
lay down with cushions on your head may work by spreading the force out more
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The problem is that with the jump, a person should accelerate up exactly of the same amount it would accelerate because of the elevator collision with the ground...
Syhprum is right.
I think that would be true in free-fall, but in this case there is a terminal velocity.
I think instead that you haven't understood well my reply [;)]
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The problem is that with the jump, a person should accelerate up exactly of the same amount it would accelerate because of the elevator collision with the ground...
Syhprum is right.
I think that would be true in free-fall, but in this case there is a terminal velocity.
I think instead that you haven't understood well my reply [;)]
Apparently. Are you saying that velocities cannot be summed?
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Apparently. Are you saying that velocities cannot be summed?
What I say is that in order to avoid crashing on the elevator's pavement, you should be shoot up with the same speed in absolute value, with respect to the elevator, that the elevator has before smashing down. Since the elevator's cabin is small, you have little space to make this acceleration (with respect to the cabin), possibly less space than the one the cabin has to decelerate by collision.
So you should be shoot up as...a cannon man, and this wouldn't be without consequences, in the sense that your body would be subject to a very high, destroying acceleration.
If the elevator's cabin were very tall, it would be different and you would have enough space to accelerate up to the requested speed with little enough average acceleration.
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you might consider it this way. From the frame of the elevator, assuming 33m/s you would need to jump with the same 'force' directed upwards. That would place you in a position relative the elevator shaft where you would seem not to move. But relative the elevator roof you would have to go through in in some tenth of a second so you would need more than 33m/s. Maybe a 100m/s would do for a elevator-roof, with some margin :) and without a roof you would still only fit 33m/s under some initial moment as you would slow down with gravity acting on you.
Seriously guys, this one is for NASA :)
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Apparently. Are you saying that velocities cannot be summed?
What I say is that in order to avoid crashing on the elevator's pavement, you should be shoot up with the same speed in absolute value, with respect to the elevator, that the elevator has before smashing down. Since the elevator's cabin is small, you have little space to make this acceleration (with respect to the cabin), possibly less space than the one the cabin has to decelerate by collision.
So you should be shoot up as...a cannon man, and this wouldn't be without consequences, in the sense that your body would be subject to a very high, destroying acceleration.
If the elevator's cabin were very tall, it would be different and you would have enough space to accelerate up to the requested speed with little enough average acceleration.
Ah! Yes I agree with you. I was saying that if you jump at the right time, you can reduce your impact velocity slightly, so it does make a "difference" when you jump, but, unfortunately, it won't do you the slightest bit of good.
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Both the Elevator & Rider are trvelling the same speed be4 the jump. The instant be4 impact , R jumps & adds force to E in a down direction as well as up for R. Due to the mass differences E will be minimally affected with the added force of the jump but R will benefit more? If the mass of E & R were the same , the jump would make no diff?