# What on earth... ?

What position would you need to adopt in a falling lift to survive?

What position would you need to adopt in a falling lift to survive?

The thing that determines whether you will survive the fall is the height the lift is falling from. If you fall a great number of floors, it doesn't make much of a difference if you are in a lift or not. Being in a free-falling lift is similar to jumping off a building of the same height and landing on something solid - the forces on your body on impact will be the same. In addition, adopting a particular position may well prove impossible.

If the lift is in free fall - so that there are no frictional forces slowing it down - then you would be "weightless" inside it, like an astronaut in space. Because you and the lift are falling at the same rate (all bodies, irrespective of their mass, fall at the same rate under gravity alone), you would not be aware that you were falling at all. You would be floating around, quite unable to adopt any position, because you wouldn't even know which way was up and which was down.

In practice, of course, you would know, because the roof of a lift is different from the floor. You would also probably hear and feel the air rushing past. And the lift would probably not be in true free fall, because it would be banging around in the shaft, but it would still be hard to position yourself, as you would be almost weightless.

Whatever position you managed to get into, one thing is certain - you would land with a bang.

At what altitude does the cabin of a passenger aircraft begin to become pressurised, and at what altitude does the pressure-level become stabilised? Also, is it just the cabin that gets pressurised, or the cargo holds, too?

As soon as the engines are on, the aircraft becomes pressurised. Before you take off, the pressure in the cabin is more than atmospheric. When the plane takes off, it rises about 90m a minute, up to about 9,000m. While the aircraft ascends, the pressure decreases outside it and also, at a slower rate, inside. The pressure-level stabilises when the plane remains at a certain altitude. At 9,000m, the most common flying-altitude, the pressure inside is what it would be outside at 2,000-2,500m. That may seem high, but several villages in the Alps are higher, and you don't get serious respiratory problems below 3,500m.

How high the aircraft can go is limited by the pressure differential between the outside and inside. The pressure inside the plane is greater than outside, so the air inside is pushing against the walls, trying to expand. That exerts pressure on the joints of the aircraft: the greater the difference in pressure, the greater the stress.

The cargo holds are pressurised as well as the cabin. The only two parts of the plane that are not pressurised are the undercarriage, where the wheels go, and a back compartment containing the flight-data recorders.

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