If level 0 is the reality, the characters in the van are at level 1. The van drops off the edge of the bridge and goes into freefall. At level 2, in the hotel, they experience the freefall as well. But then, at level 3, at the fortress, (and for that matter, in limbo) there is no freefall. Why is it so?
It is slightly odd, because other senses appear to be able to penetrate more than one layer, although they are severely attenuated.
For example, when they are in Level 2 - someone says "did you feel that, was that turbulence on the plane" (which is Level 0), to which Eames says "no, too close, Yusuf's driving probably". He doesn't say - "of course not, you wouldn't feel anything down here, must be Yusuf's driving". Then there is the Edith Piaf song used to synchronize the kick. That is played by Yusuf into Arthur's ears in Level 1, yet is heard (faintly) in Level 3. Then there is the 'second kick' that they experience when the van hits the water, this is felt in Level 3 - showing that something should be felt of the free-fall even at that layer.
If senses are attenuated with each layer it would be more realistic to think that somewhat less than free-fall would be experienced in Level 2, and some effect would be experienced in Level 3. There is too much discrepancy between the total free-fall experienced by Arthur, and the apparent normality of skiing down a mountain that the team experience in Level 3.
Still doesn't spoil my enjoyment of it though.
Best explanation is the time mechanic. Because time and other physics means for so little that deep, it could be that they are just deep enough that they do not feel it. Briefly going over the scenes of the movie, they appear to be strapped down in order to not cause this free-fall effect.
A more simpler explanation is that it is just an oversight on Nolan's part.
The freefall was to wake them up from the next level (so they would feel it!)
This is how I see the "falling" happen:
Level 1: Van falling
Felt at Level 2
Level 3 feels nothing -- can get stuck.
- How is this remedied?
- Freefall on level 2 which will bring them back from level 3.
Ok Back from level 3 up to level 2 with freefall
- Back up to level 1 with van freefall
Back up to level 0 with main freefall
Perhaps this can be explained by assuming that:
a controlled mental projection only has enough power to travel down one level, and
a kick is designed to travel up, not down.
The first premise is supported by noting that Yusuf is the dream controller for level 1, and his need to visit the men's room at level 0 causes rain at level 1 but not level 2. Arthur is the dream controller for level 2, and his free fall at level 1 causes free fall in level 2 but not level 3.
Premise (2) relies on the idea that the purpose of a kick is to wake up all of the extractors at level 0. You may have experienced something like this when you are having a nightmarish dream and something extremely violent happens in the dream that causes you to suddenly sit up in bed.
If you think about a kick as originating inside the dream and travelling upwards, its downward effects (if any) become irrelevant other than as a warning that all of the dreams are about to end. It seems that each level needs an upwards kick since Arthur scrambles around setting up a kick with the elevator at level 2. Not sure why lower levels need an upwards kick, a level 1 to level 0 kick should suffice.
One possible explanation for this is that as time multiplies with each dream level, the effects from the upper level would be felt gradually. For e.g. In level1, the van falls into the water
as a result, in level2, we get the zero gravity effect because the van is in free fall-
and in level3, we have the snow avalanche -
now, the van hit the bridge, started its free fall in water. Normally this would take about 20seconds. In level2 the free fall gives them zero gravity for a longer period, assume 10min(time is multiplied in inner dream levels). And in level3, this effect would occur even more gradually. So now we have 10min maginified, that makes it say 2-3hours. The other effects would have gradually occured in that level too. But as you know, the kick : level1 van hitting water, level2 lift propulsed with explosives resulted in the avalanche. That means, that before those effects from level1 could have reached level3, the kick from level2 actually reached level3. And the people got out of there quickly, they did not remain in level3 long enough for the effects to have taken place.