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The technical explanation of this truth:

If you are trying to negate the speed of your fall by jumping upwards, it just won't work. In free fall, you fall 5 meters the first second. By the end of the first second, you're falling at 10 meters per second, but you have only fallen 5 meters. At the end of the second second you have fallen 20 meters, and at the end of the third you'll have dropped 45 meters. The distance in meters goes as 5 x time². Now, friction and air resistance will eventually stop the downward acceleration. A human freely falling tends to peak at about 180 kilometers per hour, or about 50 meters a second. That's fast, about twice as fast as a car on a highway. An elevator might do more in a big high rise.

The simple explanation:

You are falling at the same speed the elevator is falling. Any height you gain from jumping at the end of the fall will gain you mere milliseconds and will reduce your speed by almost nothing. Even if you could jump high enough to stop your fall significantly, you would bang your head on the ceiling of the elevator and probably be worse off...

No, you're not seeing double. This is all material that used to appear in a node called jumping just before the elevator hits the ground, which was deleted. So here is its substance, again.

There's really no point in doing it. Not because of little things like terminal velocity and air resistance (you're not going to fall for long enough to get anywhere near terminal velocity), but because of Big Things. Things like Physics and conservation of energy. One way to see this is to set up some equations and solve them. But if you want to verify this without all that nasty mucking about with forces and the need actually to understand Physics, you can cheat.

Suppose you're in a lift (as they're called in English) at some height, and you start freefalling along with the lift. Eventually, no matter what faces you pull at the security camera behind the mirror, lightbulbs you shatter, or jumps you perform, you will smash into the floor (the lift will also do so). In your case, you will have converted your potential energy (from being at that height initially) into kinetic energy (at height , when you crash into non-tomato ketchup). So it's always the same kinetic energy, and always the same velocity that you crash with.

OK?

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