Another physics question...
Discussion
gasblaster said:
It's an old question, but:
Your lift cable has snapped and now you are hurtling towards your destiny at the bottom of a tower block. Would jumping into the air at the last minute reduce the impact?
well, yes, but not by much. If you could jump like the incredible hulk no prob, other than bursting through the roof of the lift.
If you jump, while you're going upwards relative to the lift, you'll still be going downwards relative to the lift shaft (although slightly slower). Then as you start to come down again (relative to the lift) you'll accelerate back to the speed of the lift. Relative to the lift shaft, I don't reckon it'll make any significant difference...
wolves_wanderer said:
Unless you could jump at the same speed as the lift is falling then no.
Even if you could though, isn't the push you generate met with an equal and opposite action, ie, you pushing the lift down as you press away to jump up? So then it comes down to the mass of the lift mechanism that is falling, it's drag, the bearing/friction drag, the force you can generate to accelerate the lift downwards, and the resultant upwards force given to yourself... f=ma and all that.
Dave
Mr Whippy said:
Unless you could jump at the same speed as the lift is falling then no.
Even if you could though, isn't the push you generate met with an equal and opposite action, ie, you pushing the lift down as you press away to jump up? So then it comes down to the mass of the lift mechanism that is falling, it's drag, the bearing/friction drag, the force you can generate to accelerate the lift downwards, and the resultant upwards force given to yourself... f=ma and all that.
Dave
I think I have worked out that if you were the current world record high-jumper and the lift fell from a 50 metre building, you would reduce final velocity by around one third. Hey ho.
gasblaster said:
Unless you could jump at the same speed as the lift is falling then no.
Even if you could though, isn't the push you generate met with an equal and opposite action, ie, you pushing the lift down as you press away to jump up? So then it comes down to the mass of the lift mechanism that is falling, it's drag, the bearing/friction drag, the force you can generate to accelerate the lift downwards, and the resultant upwards force given to yourself... f=ma and all that.
Dave
I think I have worked out that if you were the current world record high-jumper and the lift fell from a 50 metre building, you would reduce final velocity by around one third. Hey ho.
There's not enough room for Sotomayor's (sp?) run up though
Liszt said:
Mythbusters said no.
That's right. Mythbusters (Discovery Channel most days/nights) did exactly that experiment and dropped a lift 8 stories. The specially rigged crash test dummy inside, complete with jumping mechanism clearly showed that the forces involved were high enough to kill someone doing trying to do the same. The forces were virtually the same as if the dummy had simply been dropped from 8 stories up
It would help a little.
Say the lift fell 50 metres completely unimpeded. Give or take a bit it would fall for 3 seconds before hitting the ground at a speed of 30m/s. If just before it hit, you tried to jump as high as you could, you'd probably be able to throw yourself at 1.5m/s up from the bottom of the lift. If you timed it just right, your feet would be leaving the floor of the lift just as it hit the ground. Your body would then be travelling downwards at 30-1.5 = 28.5 m/s relative to the ground which is obviously a little bit better than hitting the ground at 30 m/s (or 65mph instead of 70mph).
Say the lift fell 50 metres completely unimpeded. Give or take a bit it would fall for 3 seconds before hitting the ground at a speed of 30m/s. If just before it hit, you tried to jump as high as you could, you'd probably be able to throw yourself at 1.5m/s up from the bottom of the lift. If you timed it just right, your feet would be leaving the floor of the lift just as it hit the ground. Your body would then be travelling downwards at 30-1.5 = 28.5 m/s relative to the ground which is obviously a little bit better than hitting the ground at 30 m/s (or 65mph instead of 70mph).
gasblaster said:In theory no. Strangely I never felt the need to actually test it in practice though
The centrifugal brakes and dampers in the pit would probably help more than mere jumping 
Sorry, I know it's not in keeping with the spirit of the thread
If brakes didn't work but the dampers did, would it shoot you back up to the top again?
I read somewhere recently (though it may have been untrue) that there has never been a single fatality resulting from a lift failing in normal use. Anywhere. Ever.
When you think of how many lifts there are, and how many journeys there are taken in lifts every day, that is quite comforting really.....
When you think of how many lifts there are, and how many journeys there are taken in lifts every day, that is quite comforting really.....
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