Could I survive in a falling elevator by jumping at the last second?

07 March 2017

Question

Could I survive in a falling elevator by jumping at the last second?

We put Addie's question to physicist Michael Conterio...

Michael - This is quite a shame because when I was young I had this exact same question. It would be brilliant just to be able to jump at the end and save my life but, as it turns out, you can’t, sadly.

If you think about it, if you imagine falling all the way down from a few floors up, and of course you’re building up speed, you’re building up momentum as you go down. And when you reach the bottom, it’s the fact that in order for you to lose all that momentum, the floor basically has to push on you very hard, and it pushes on you so hard that it hurts - it breaks your legs and kills you.

So if you could do a little jump just before you reach the ground you’re not going to be able to get rid of all that momentum. You can only jump a little height compared to how much you’ve fallen. So you wouldn’t have the strength to do it. If you did have the strength to do it, you’d still basically break you legs while doing it. And there’s also the fact that if it’s in freefall, so the life is just dropping, there’s no friction keeping it up or anything, then you would be in freefall as well. That means that the slightest touch on the bottom of the lift you would start drifting away from it. Your acceleration would be slightly different to the lift.

So there’s a big result in general relativity which basically says that being in freefall inside a lift like this is basically the same as being out in deep space and just floating around in a rocket ship, so you’d experience almost like zero gravity while you were falling for those few brief moments.

Chris - I suppose one way you could also look at this is to say that in order to have movement which is equal and opposite to the falling of the lift, you’ve got to jump as fast in the opposite direction the lift is carrying you downwards. So you’ve got to be going upwards at the same speed as the lift would be going downwards and you splatting on the ground. So in order to propel yourself at that rate anyway you’d have to experience the same forces on your legs to accelerate you, wouldn’t you in the first place, so you’d still do damage to yourself achieving a monumental jump like that?

Michael - Yeah. It’s basically the same odds and saying that you’re going to be accelerated to whatever speed you’ve acheived by falling with the lift in the same amount of time as it would take you to jump, which is a lot of force in a very little time.